====== Past Prelims ====== Dexter has two binders with prelim questions dating back to the 1970s. This page is to those binders what the [[private:ebrb:home|EBRB]] is to the Big Red Binder of teaching tips. When adding your questions, please update each index (professor, subject, date ...?) so that this material can be searched easily. The table can be sorted in different ways by clicking on the column headings. ^ Date ^ Student ^ Professor ^ Subject ^ Link ^ | 04/12/05 | Joe Converse | Eliot Quataert | Fluids | [[past_prelims#converse_fluids|link]] | | 04/12/05 | Joe Converse | Jon Arons | Plasmas | [[past_prelims#converse_plasmas|link]] | | 04/12/05 | Joe Converse | Chung-Pei Ma | Cosmology | [[past_prelims#converse_cosmology|link]] | | unknown | unknown | Leo Blitz | Galaxies | [[past_prelims#unknown_galaxies|link ]] | | unknown | Evan Levine | Leo Blitz | Galaxies | [[past_prelims#levine_galaxies|link ]] | | 05/01/06 | Kristen Shapiro | Leo Blitz | Galaxies | [[past_prelims#shapiro_galaxies|link ]] | | unknown | unknown | Leo Blitz | Galaxies | [[past_prelims#unknown_galaxies|link ]] | | 07/14/06 | Onsi Fakhouri | Leo Blitz | Galaxies | [[past_prelims#fakhouri_galaxies|link ]] | | 06/01/06 | Daniel Perley | Eugene Chiang | Radiation | [[past_prelims#perley_radiation|link]] | | 06/01/06 | Daniel Perley | Alex Filippenko | Cosmology | [[past_prelims#perley_cosmology|link]] | | 06/01/06 | Daniel Perley | Josh Bloom | High Energy | [[past_prelims#perley_high_energy|link]] | | 06/11/07 | Jeffrey Silverman | Eliot Quataert | Stars | [[past_prelims#silverman_stars|link]] | | 06/11/07 | Jeffrey Silverman | James Graham | ISM | [[past_prelims#silverman_ism|link]] | | 06/11/07 | Jeffrey Silverman | Eugene Chiang | Fluids | [[past_prelims#silverman_fluids|link]] | | 01/29/07 | Andrew Wetzel | Eliot Quataert | Fluids | [[past_prelims#wetzel_fluids|link]] | | 01/29/07 | Andrew Wetzel | Jon Arons | High Energy | [[past_prelims#wetzel_high_energy|link]] | | 01/29/07 | Andrew Wetzel | Marc Davis | Cosmology | [[past_prelims#wetzel_cosmology|link]] | | 02/05/08 | Peter Williams | Chung-Pei Ma | Cosmology | [[past_prelims#williams_cosmology|link]] | | 02/05/08 | Peter Williams | Steve Stahler | Star Formation | [[past_prelims#williams_star_formation|link]] | | 02/05/08 | Peter Williams | Eugene Chiang | Radiation | [[past_prelims#williams_radiation|link]] | | 06/03/08 | Amber Bauermeister | Chung-Pei Ma | Cosmology | [[past_prelims#bauermeister_cosmology|link]] | | 06/03/08 | Amber Bauermeister | Al Glassgold | ISM | [[past_prelims#bauermeister_ism|link]] | | 06/03/08 | Amber Bauermeister | Eugene Chiang | Fluids | [[past_prelims#bauermeister_fluids|link]] | | 06/05/08 | Nicholas McConnell | Steve Stahler | Star Formation | [[past_prelims#mcconnell_star_formation|link]] | | 06/05/08 | Nicholas McConnell | Eliot Quataert | Stars | [[past_prelims#mcconnell_stars|link]] | | 06/05/08 | Nicholas McConnell | Eugene Chiang | Fluids | [[past_prelims#mcconnell_fluids|link]] | | 06/12/09 | Matt George | Geoff Bower | Radiation | [[past_prelims#george_radiation|link]] | | 06/12/09 | Matt George | Eliot Quataert | Stars | [[past_prelims#george_stars|link]] | | 06/12/09 | Matt George | Carl Heiles | ISM | [[past_prelims#george_ism|link]] | | 02/27/09 | Josh Shiode | Eliot Quataert | Stars | [[past_prelims#shiode_stars|link]] | | 02/27/09 | Josh Shiode | Al Glassgold | ISM | [[past_prelims#shiode_ism|link]] | | 02/27/09 | Josh Shiode | Eugene Chiang | Fluids | [[past_prelims#shiode_fluids|link]] | | 08/28/09 | Vincent Viscomi | Martin White | Cosmology | [[past_prelims#viscomi_cosmology | link]] | | 08/28/09 | Vincent Viscomi | Eliot Quataert | Stars | [[past_prelims#viscomi_stars | link ]] | | 08/28/09 | Vincent Viscomi | Geoff Bower | Radiation | [[past_prelims#viscomi_radiation | link ]] | | 12/11/09 | Jonnie Pober | Geoff Bower | Radiation | [[past_prelims#pober_radiation | link ]] | | 12/11/09 | Jonnie Pober | Leo Blitz | Galaxies | [[past_prelims#pober_galaxies | link ]] | | 12/11/09 | Jonnie Pober | Martin White | Cosmology | [[past_prelims#pober_cosmology | link ]] | | 12/14/09 | Mike McCourt | Eliot Quataert | Stars | [[past_prelims#mccourt_stars | link ]] | | 12/14/09 | Mike McCourt | Geoff Bower | Radiation | [[past_prelims#mccourt_radiation | link ]] | | 12/14/09 | Mike McCourt | Martin White | Cosmology | [[past_prelims#mccourt_cosmology | link ]] | | 02/04/10 | Chat Hull | Geoff Bower | Radiation | [[past_prelims#hull_radiation | link ]] | | 02/04/10 | Chat Hull | Leo Blitz | Galaxies | [[past_prelims#hull_galaxies | link ]] | | 02/04/10 | Chat Hull | Steve Stahler | Star Formation | [[past_prelims#hull_star_formation | link ]] | | 08/10/10 | James McBride | Geoff Bower | Radiation | [[past_prelims#mcbride_radiation | link ]] | | 08/10/10 | James McBride | Eliot Quataert | Stars | [[past_prelims#mcbride_stars | link ]] | | 08/10/10 | James McBride | Carl Heiles | ISM | [[past_prelims#mcbride_ism | link ]] | | 09/03/10 | Aaron Lee | Eliot Quataert | Stellar Interiors | [[past_prelims#lee_stellar_interiors | link ]] | | 09/03/10 | Aaron Lee | Carl Heiles | ISM | [[past_prelims#lee_ISM | link ]] | | 09/03/10 | Aaron Lee | Steve Stahler | Fluids | [[past_prelims#lee_fluids | link ]] | | 09/17/10 | Adam Morgan | Eliot Quataert | Stars | [[past_prelims#morgan_stars | link ]] | | 09/17/10 | Adam Morgan | Geoff Bower | Radiation | [[past_prelims#morgan_radiation | link ]] | | 09/17/10 | Adam Morgan | Alex Filippenko | Cosmology | [[past_prelims#morgan_cosmology | link ]] | | 08/06/10 | Chris Klein | Leo Blitz | Galaxies | [[past_prelims#klein_galaxies | link ]] | | 08/06/10 | Chris Klein | Geoff Bower | Radiation | [[past_prelims#klein_radiation | link ]] | | 08/06/10 | Chris Klein | Steve Stahler | Star Formation | [[past_prelims#klein_star_formation | link ]] | | 12/12/11 | Casey Stark | Leo Blitz | Galaxies | [[past_prelims#stark_galaxies|link]] | | 12/12/11 | Casey Stark | Eliot Quataert | Fluids | [[past_prelims#stark_fluids|link]] | | 12/12/11 | Casey Stark | Martin White | Cosmology | [[past_prelims#stark_cosmology|link]] | | 08/30/12 | Francesca Fornasini | Eugene Chiang | Radiation | [[past_prelims#fornasini_radiation|link]] | | 08/30/12 | Francesca Fornasini | Leo Blitz | Galaxies | [[past_prelims#fornasini_galaxies|link]] | | 08/30/12 | Francesca Fornasini | Josh Bloom | High Energy | [[past_prelims#fornasini_highenergy|link]] | | 12/03/12 | Sedona Price | Leo Blitz | Galaxies | [[past_prelims#price_galaxies|link]] | | 12/03/12 | Sedona Price | Dan Kasen | Radiation | [[past_prelims#price_radiation|link]] | | 12/03/12 | Sedona Price | Chung-Pei Ma | Cosmology | [[past_prelims#price_cosmology|link]] | | 12/15/12 | Lauren Weiss | Dan Kasen | Radiation | [[past_prelims#weiss_radiation|link]] | | 12/15/12 | Lauren Weiss | Chung-Pei Ma | Cosmology | [[past_prelims#weiss_cosmology|link]] | | 12/15/12 | Lauren Weiss | Mariska Kriek | Galaxies | [[past_prelims#weiss_galaxies|link]] | | 02/01/13 | Isaac Shivvers | Dan Kasen | Radiation | [[past_prelims#shivvers_radiation|link]] | | 02/01/13 | Isaac Shivvers | Chung-Pei Ma | Cosmology | [[past_prelims#shivvers_cosmology|link]] | | 02/01/13 | Isaac Shivvers | Mariska Kriek | Galaxies | [[past_prelims#shivvers_galaxies|link]] | | 09/13/13 | Nick Hand | Martin White | Cosmology | [[past_prelims#hand_cosmology|link]] | | 09/13/13 | Nick Hand | Eliot Quataert | Fluids | [[past_prelims#hand_fluids|link]] | | 09/13/13 | Nick Hand | Mariska Kriek | Galaxies | [[past_prelims#hand_galaxies|link]] | | 12/20/13 | Kaylan Burleigh | Eliot Quataert | Stars | [[past_prelims#burleigh_stars|link]] | | 12/20/13 | Kaylan Burleigh | Dan Kasen | Radiation | [[past_prelims#burleigh_radiation|link]] | | 12/20/13 | Kaylan Burleigh | Uros Seljak | Cosmology | [[past_prelims#burleigh_cosmology|link]] | | 01/28/14 | Eve Lee | Eliot Quataert | Stars | [[past_prelims#elee_stars|link]] | | 01/28/14 | Eve Lee | Chung-Pei Ma | Fluids | [[past_prelims#elee_fluids|link]] | | 01/28/14 | Eve Lee | Mariska Kriek | Galaxies | [[past_prelims#elee_galaxies|link]] | | 04/18/14 | Lea Hirsch | Mariska Kriek | Galaxies | [[past_prelims#hirsch_galaxies|link]] | | 04/18/14 | Lea Hirsch | Steve Stahler | Star Formation | [[past_prelims#hirsch_star_formation|link]] | | 12/05/14 | Carina Cheng | Chung-Pei Ma | Fluids | [[past_prelims#cheng_fluids|link]] | | 12/05/14 | Carina Cheng | James Graham | Instrumentation | [[past_prelims#cheng_instrumentation|link]]| | 03/05/15? | Jason Wang | Mariska Kriek | Galaxies | [[past_prelims#wang_galaxies|link]] | | 03/05/15? | Jason Wang | Chung-Pei Ma | Fluids | [[past_prelims#wang_fluids|link]] | | 03/05/15? | Jason Wang | James Graham | Instrumentation | [[past_prelims#wang_instrumentation|link]] | | 2015 | Danny Goldstein | Josh Bloom | High Energy | [[past_prelims#goldstein_high_energy|link]] | | 2015 | Danny Goldstein | Aaron Parsons | Radiation | [[past_prelims#goldstein_radiation|link]] | | 2016 | Tom Zick | Aaron Parsons | Radiation | [[past_prelims#zick_radiation|link]] | | 2016 | Tom Zick | Martin White | Cosmology | [[past_prelims#zick_cosmology|link]] | | 2016 | Tom Zick | Mariska Kriek | Galaxies | [[past_prelims#zick_galaxies|link]] | | 2016 | Gerry Zhang | Martin White | Cosmology | [[past_prelims#zhang_cosmology|link]] | | 2016 | Gerry Zhang | Aaron Parsons | Radiation | [[past_prelims#zhang_radiation|link]] | | 2016 | Gerry Zhang | Mariska Kriek | Galaxies | [[past_prelims#zhang_galaxies|link]] | | 11/2016 | Alex Krolewski | Martin White | Cosmology | [[past_prelims#krolewski_cosmology|link]] | | 11/2016 | Alex Krolewski | Aaron Parsons | Radiation | [[past_prelims#krolewski_radiation|link]] | | 11/2016 | Alex Krolewski | Mariska Kriek | Galaxies | [[past_prelims#krolewski_galaxies|link]] | | 5/2017 | Deepthi Gorthi | Dan Weisz | Stellar Populations| [[past_prelims#gorthi_stellar_populations|link]] | | 5/2017 | Deepthi Gorthi | Chung-Pei Ma | Fluids | [[past_prelims#gorthi_fluids|link]] | | 5/16/17 | Wren Suess | James Graham | Instrumentation | [[past_prelims#suess_instrumentation|link]] | | 5/16/17 | Wren Suess | Chung-Pei Ma | Fluids | [[past_prelims#suess_fluids|link]] | | 5/2017 | Nick Kern | Uros Seljak | Cosmology | [[past_prelims#kern_cosmology|link]] | | 5/2017 | Nick Kern | Aaron Parsons | Radiation | [[past_prelims#kern_radiation|link]] | | 5/2017 | Nick Kern | Eliot Quataert | Stars | [[past_prelims#kern_stars|link]] | This body of text holding the questions may grow quite large, and could conceivably be separated onto individual pages for each person's prelim. For now, it is kept on a single page to enable faster searching, e.g., you can use Ctrl+F to find how often the phrase "Compton scattering" is asked about. ===== Converse Fluids ===== **Eliot Quataert** - What is the criteria for gravitational stability in a rotating disk? - What is Toomre's Q parameter? Explain it physically. - What are the assumptions about the perturbations behind this? - What about non-axisymmetric perturbations? - Why is this not just the Jeans instability? - The observed Q is about 1 for many spirals. Can you give an argument/reason why this would be so? - Assuming Q~1, derive the volume density using the equation for vertical hydrostatic equilibrium. - Assuming the Milky Way is an accretion disk, write an expression for the viscous time in terms of the orbital period. Assume an \(\alpha\)-viscosity model. What is this time scale at the solar circle? - How might you get more efficient transport in a galaxy? - Is the Galactic disk stable to the MRI? - What is \(\alpha\) for the MRI? - What sort of waves are observed in helioseismology? - Are these P-modes or G-modes? What is the difference between them? - Why are only P-modes seen? - What is the origin of the characteristic ~5 minute period of these waves? ===== Converse Plasmas ===== **Jon Arons** - Can a light wave of any frequency travel through a uniform plasma? If not what is the limit? - Write down the dispersion relation for such a wave. - What is the plasma frequency? What is the physics behind when \(\omega=\omega_p\)? - Solve the equation of motion for an electron's velocity in an oscillating electric field. Is there a current? - What current allows EM waves to propagate in vacuum? - Add this to the previous current. Is there a condition such that the total current is zero? - Why do waves stop propagating when \(\omega=\omega_p\)? - What happens when a strong, transverse, background B-field is added? - Imagine \(B\rightarrow\infty\). Is there any sideways current? - What are MHD waves? Explain them physically. - Is displacement current important in MHD waves? - What is the polarization of Alfven waves? What currents are associated with it? - Does \(\vec{E}\times\vec{B}\) drift produce a current? - Is curvature drift important as \(T\rightarrow 0\)? - Write the equation of motion for a particle in a B-field. What is the intrinsic timescale for such motion? - How do the frequency of MHD waves compare to this timescale? - What is polarization drift? What direction is it in? - Under what conditions can you make the polarization drift go away? - What happens to Alfven waves if \(v_A=c\)? - What role does displacement current play then? ===== Converse Cosmology ===== **Chung-Pei Ma** - What is the most abundant particle in the universe? - Estimate the number density of photons. Where are they? - How can you estimate the number density from the CMB? - How does the number density depend on temperature? - How does the number density of neutrinos compare to the photons? Does it depend only on T? - When did neutrinos decouple? - Why are the photon and neutrino temperatures different? - How does the number density scale with scale factor? - What about the energy density? - What is the current best constraint on the number of neutrino families? - How does BBN constrain it? - What determines how a evolves? Write the equation. - What happens to a if there are more neutrinos? How does this effect BBN? - What does BBN tell us about \(\Omega_b\)? - How do different values of \(\Omega_b\) effect BBN abundence ratios? - Draw typical CDM fluctuation spectrum. These are fluctuations of what? - Why is there a special scale in P(k)? - What size scales grow first? - Why is \(\Omega_\Lambda\) considered by some to be the ugliest number in physics? - What is the significance of the Plank Mass? What is it's value? - What does CMB power spectrum look like? - What is the physics of acoustic oscillations on the surface of last scattering? What is sound speed? - Why do baryons oscillate? - What is Thompson scattering? - What is the significance of the size scale of the first peak? ===== Unknown Galaxies ===== **Leo Blitz** - What is the IMF? - Does it refer to the total number of stars or total mass? - How is it measured? - What observations would you make to establish the IMF? Give an example of what system you would observe. - How do you establish cluster membership? - How do you measure stellar masses? - If you were to use the Pleiades, the mass function would extend only to B stars. So - how do you get the O-star mass spectrum? - What is the normalization of the IMF? - Is this a good method for getting the IMF to low masses? - How would you get the IMF for low mass stars? - The first IMF measurement was Salpeter's in 1956, at which time there were not many parallax measurements available. How did he proceed? - What is the main-sequence lifetime of a G star? - What is an easier distance estimate than parallax measurement? - What is the traditional form of the IMF? - What is the index of the power law? - Why can't a single power law with \(\alpha=-2.3\) describe the entire population? - Do all galaxies have the same IMF? - Where is most of the mass -- low mass or high mass stars? - At which end of the IMF would you focus (to determine whether all galaxies have the same IMF)? - Imagine a galaxy with interstellar gas pressure that is very different from that in the solar neighborhood, e.g., the center of the Milky Way. Would the IMF be different? - Write down the Jeans mass. - Imagine a star cluster with \(10^3\) stars and a galaxy cluster with \(10^3\) galaxies. How do the relaxation times compare? - What is the criterion for a relaxed system? - What is the interaction rate? - What is the crossing time for a self-gravitating system? ===== Levine Galaxies ===== **Leo Blitz** - What is a galaxy? - How is it different from a globular cluster? - What are the properties of the smallest galaxies? - What shape do these galaxies have? - What is their gas and dust content? - Where are they located? - How do you characterize a distribution of stars? (some answers . . .) - surface brightness profiles - velocity - velocity dispersion - luminosity function - How do you measure the luminosity function? - How do you ensure completeness for the faintest stars? (ans: proper motion surveys) - Is the luminosity function intrinsic to a stellar population? - What are the units of an initial mass function? - What is the S-Z effect? - Draw a diagram and sketch spectra. - What do I see if I observe at 50 MHz towards the cloud versus in other directions? - What is the cross-over frequency on the plot (where the up-scattered and unscattered spectra have the same intensity)? (ans: Leo says 212 GHz, C-P says 217 GHz) - Is the excess or deficit easier to detect? Why? - How does the magnitude of the effect depend on the distance to the cloud? - Through what radiative process does the cluster gas emit? At what temperature is this gas? - How does this emission depend on the size and density of the cloud? - How does the amount of S-Z absorption depend on the size and density of the cloud? - What can we use the S-Z effect to measure? What cosmological parameters? - What is the ratio of mass in cluster gas to mass in galaxies? - Consider a disk galaxy differentially rotating. We observe a two-dimensional velocity field. - Draw the isovelocity contours. - What is the rotation curve that produces this? - What does this imply about the density profile as a function of radius in the two regions? - How does this compare with the luminosity profile of the galaxy? - What mass components make up the galaxy? - If you see closed loops in the spider diagram, what does that mean? - How is the circular velocity related to the gravitational potential? - Where is the initial mass function measured? - What observational evidence tells us that the IMF is the same (similar) are different locations? ===== Shapiro Galaxies ===== **Leo Blitz** - What kind of Galaxy is the Milky Way and how do you know this information? - How do you trace spiral arms? - Draw a picture of how you would get information about structure of the MW from the 21-cm line. - What do you do with the measured velocity information? How do you interpret the line profile? - How do you figure out where the spiral arms are? - Compare inside the outside the solar circle. - How do I measure the rotational velocities of the gas outside the solar circle? - How is the rotation curve measured outside of the solar circle (not using HI)? - What kinds of stars are used? - How do you measure the velocities of O stars? - O stars form from molecular gas. What other tracer can you use to get the velocities? - It has been known for some time that the MW is a spiral galaxy -- even prior to HI observations. What evidence was used? - What about the Oort constants? - What is the mass-to-light ratio of the sun? - What type of galaxies have M/L > 1? - Are there galaxies with M/L < 1? - What is the Eddington luminosity? Give an expression. - Motion in a disk of a galaxy is non-circular orbits. What is an epicycle, and what is epicyclic motion? What is the epicyclic frequency? Is there a frame in which this orbit is closed? Can you always find a rotating frame of reference where the orbit is closed? - Draw what a closed orbit looks like in the rotation frame. What quantities does the epicycle frequency depend on? What else do I need to know other than the rotation frequency? What is the expression of an epicyclic frequency? - What do the isovelocity contours look like fro a spheroidal galaxy? What if the galaxy is not rotating? ===== Unknown Galaxies ===== **Leo Blitz** - What is dust? - What sizes and shapes does it have? What is the distribution of sizes? - What is the chemical composition? What form of carbon? What stuff does this correspond to on Earth? - What other types of things can form dust? - Who discovered dust? (Answer: Trumpler, Harold Weaver's father in law) - What is the evidence for dust? - Why is knowing about dust important for studying galaxies? - Tell me about dynamical friction. - What is the mass dependence of the force? Why? - What is the mass-to-light ratio? Why do we care about it? - How do we determine M/L in galaxies? What do we measure? - How do we get distance? - How do we get mass? How do we measure \(v_{\rm circ}\)? - What are contours of velocity for solid body rotation? (Spider Diagram) - When do max velocities form a line and when are they warped? - What state of matter does H\(\alpha\) come from? How does this compare to stellar orbits? - How does M/L change with radius? - What is the shape of the dark matter potential? - If we have ellipsoid, what happens to the orbits? - What is an epicycle in the dynamical sense? - Are two (epicycle) reference frames consistent? - A closed elliptical orbit in the rotating frame looks like what? - Can I use epicyclic approximation to describe the gas discussed previously? - What are the units of \(\Phi\)? - How do we determine \(v_{\rm c}\) from \(\Phi_{\rm r}\)? - If we take a census of GMCs in galaxies \(\frac{dN}{dM}=\frac{1}{M_0}\left(\frac{M}{M_0}\right)^{-\alpha}\). In M33, \(\alpha = 2.3\), other galaxies have \(\alpha=1.6\). What is fundamentally different between these galaxies? - When most mass is in small clouds, what happens physically as //M// goes to zero? ===== Fakhouri Galaxies ===== **Leo Blitz** - What kind of galaxy is the milky way? - How do we know? - Spiral arms first identified how? - In other galaxies how do we understand arms? - How do we know galaxy is a disk? - Are all stars associated with galaxies? - They form there, but do they stay bound? - Hypervelocity stars? How can they attain escape velocities? - Any near the sun? What about pulsars? - What are the Jeans equations? - Write them down. - Is there an energy equation for stellar systems? - What are the sources of energy changes? - Quantify how spiral arms are found: derive radial velocity of gas along a line of sight in galactic coordinates. - Can you always use \(v_{\rm los}\) to get the distance from the sun? - What if the orbits are elliptical? Does there exist distance degeneracy? - Draw the rotation curve of the Milky Way. - Why is there a bump in the rotation curve? - Given the presence of a bar, does the bump represent \(v_{\rm circ}\)? - Does \(v_{\rm circ} \rightarrow 0\) near the center of the galaxy? - What's the potential of the bulge? - What's \(\rho ( r )\) for an isothermal sphere? - What's the surface density of the galaxy locally? ===== Perley Radiation ===== **Eugene Chiang** Suppose you have a star, surrounded by a highly ionized accretion disk. The disk has a radius r, a temperature T, and density n, both functions of r. The disk is optically thin. - Write an expression for the volume emissivity as a function of n, T, and r. - Write an expression for the volume emissivity due to scattering as a function of n, T, and r. - Now assume that the disk is optically thick and heated from within, with the heat originating at the mid-plane due to viscosity effects. (The origin of the heating is not important.) - An observer looking down at the disk from above measures an apparent temperature Teff. With this knowledge, how would you estimate the temperature at the mid-plane? - What is Fick's Law? Explain, and use it to estimate the mid-plane temperature. - What is the equation for the energy density of a blackbody? - What is LTE? - For matter in LTE, what are the relative populations of two energy levels as a function of energy and temperature? - What physical condition is required for matter to be in LTE? - How do you determine the characteristic time for spontaneous de-excitation of an atom from one level to another? - What is the collisional expectation time for molecules a gas at temperature T? - For LTE, should the collisional expectation time be shorter than, or longer than, the spontaneous de-excitation time? ===== Perley Cosmology ===== **Alex Filippenko** - What is the cosmic microwave background radiation? - Do we have any direct evidence that the temperature of the CMB was higher in the past? - The temperature CMB is not the same in all directions. What is the approximate level of variation, and what is its origin? - What is the origin of small-scale fluctuations in the CMB? What two forces are fighting each other? - Explain why some angular scales are preferred over others in the CMB. - Qualitatively, what determines the physical sizes of these fluctuations? - Draw a power spectrum of the CMB. What is the approximate angular scale of the first peak? - Present a purely geometric derivation for what we might naively expect the size of CMB fluctuations on the sky to be. - The answer to (8 * is too small by a factor of 103. Explain the discrepancy, and write down an order-of-magnitude expression for the correct angular scale. - What does the angular scale of the first peak tell us about the universe? - What are the current best limits on the universe's curvature? - Will we ever be able to determine whether the universe is flat, open, or curved, if in fact the universe is flat? - What determines the relative heights of the different peaks of the CMB? - What is the current WMAP estimate of the amount of baryonic matter in the universe? - Why does the CMB power spectrum fall off dramatically at high l? - Do you know the term for the scale at which this happens? - What do the very lowest multipole scales tell us about the geometry of the universe? - How else might we determine whether our universe is finite in size, on scales less than a Hubble radius? - How do we know that redshifts are due to the expansion of the universe, and not expansion into a preexisting space or 'tired light'? - Can we use the surface brightness of cosmological features to refute the possibility that the universe is expanding into a preexisting space? How should surface brightness scale with the redshift z? - What fraction of the universe is non-baryonic dark matter? - What are some candidates for non-baryonic dark matter? Of these, which is the preferred model? - What evidence do we have for the existence of dark matter? - Do we have any direct evidence of dark matter? - What fraction of the universe is things that we can see – stars and gas? - Compare this to the baryonic content of the universe from the CMB and nucleosynthesis. What accounts for the discrepancy? - Why was the hot gas not detected until recently? What part of the spectrum does it emit in? - How can we constrain the fraction of baryonic dark matter due to MACHOs? - What fraction of MACHOs should be in galactic halos? - Where is the best place to look in carrying out surveys for MACHOs? - Are there any other constraints on the amount of baryonic matter? - Explain the role of deuterium in nucleosynthesis after the big bang. - What does the D/H ratio tell us? - Are the predictions of Big Bang Nucleosynthesis based on different isotopes in total agreement, or are there any inconsistencies? - Write down an equation for the acceleration of the universe and the associated equation of state. - For the cosmological constant, what is w ? Explain how this causes the universe to accelerate as it expands. - Why was the cosmological constant first introduced? - Would such a universe be stable? - Can you provide a laboratory example of vacuums with different energy densities? ===== Perley High Energy ===== **Josh Bloom** * What are gamma-ray bursts? * What are gamma rays? * How are GRBs detected? * There are three physical effects used in detecting gamma rays. What are they? * What is Compton scattering? * What is the typical fluence of a GRB? * How many total photons are detected by an instrument during a typical GRB? * What is the total isotropic energy release of a GRB? Assume a luminosity distance of 1 Gpc. * What constraint on the GRB comes from the variability timescale? * Assume that the physical scale from (above) is correct. What is the maximum mass that can be placed in this region without forming a black hole? * Suppose that the \(10^{52}\) erg estimate above is released on a timescale of seconds. How does the luminosity compare with the Eddington luminosity of a 100-solar mass black hole? * What is the Eddington luminosity? Derive it as a function of mass. * What is the Thompson cross-section? * What are some possible energy sources that could possibly provide up to \(10^{52}\) ergs? * Estimate the amount of gravitational energy available to power a GRB. * What is the typical mass of a neutron star? A white dwarf? What supports these objects? * Explain the origin of degeneracy pressure. * What is the limiting mass of a white dwarf called, and approximately what is it? * Is there an upper mass-limit for a neutron star? * How does the radius of a degenerate object depend on its mass? * Suppose a neutron star is rapidly spinning. Is there an upper limit for the amount of rotational energy; and if so, what is it? * Estimate the amount of magnetic energy in a highly magnetized neutron star. * How do we know that GRBs are relativistic? * What is the compactness problem? * Derive why the apparent duration of an event emitted by a source moving towards us at relativistic velocities differs by a factor of γ2 from its rest-frame duration. ===== Wetzel Fluids ===== **Eliot Quataert** - What is the basis of fluid mechanics? - Start with kinetic theory: define a distribution function (physically) - Can you measure it? - What about for photons? - What assumptions go into a measurement? - What is the Boltzmann equation? - How are density, pressure, and energy related to the distribution function? Why? - How are the variables of the distribution function related to those of density, pressure, etc.? - What assumptions are involved in closing the hierarchy? - Physically, why is the moment of collision operator set to zero (what are the assumptions of kinetic theory)? - What fluid terms are important if have deviation from Maxwell-Boltzmann distribution? - Estimate the conductivity and viscosity in the room. When are they important? - What does the Kolmogorov spectrum of turbulence describe physically? - What it is a power spectrum of? - Can you (heuristically) derive the spectrum? - What is the length scale of interest? - Which velocity are you interested in? ===== Wetzel High Energy ===== **Jon Arons** - What are cosmic rays? - How do we observe them? What is their background? - Draw a spectrum of cosmic ray protons - How low does the energy spectrum go? - What happens to the spectrum as we go below the GeV range? - Why does the spectrum drop? - What does the sun put out? - What is the spectral distribution in the galaxy? - What is the role of B-fields? - What is the anisotropy of the flux? - How isotropic is sky from pion production? - What is the pion production reaction? - Do you care whether the ISM particles are atomic or molecular? - Are cosmic rays concentrated in the galactic plane (from mapping of gamma rays)? - What is the scale height of cosmic rays relative to the gas? - What is the time scale for cosmic rays to leave the galaxy (diffuse out)? - What is the average lifetime of cosmic rays? What sets it? Can you measure it? - What is the source of cosmic rays? Why? - How are they accelerated to high energies? ===== Wetzel Cosmology ===== **Marc Davis** - What is the evidence for the big bang? - How much deuterium do we see? How much helium? - Why do we see helium & deuterium at all? - What happens in the first few seconds of the universe? - What sets the ratio of neutrons to protons in the early universe? Draw the ratio as a function of temperature. - Why does the ratio freeze out? - What is the analogous freeze-out that happens at recombination? - Hot vs. cold dark matter: draw the power spectrum of both (linear and non-linear regime). - What do hot dark matter particles do (as opposed to cold dark matter)? - What is the scale whether hot dark matter power decreases at high //k//? - What is the cosmological limitation on the mass of the neutrino (from the critical density)? - What is the density of neutrinos today? How do we know this? - Why does the dark matter power spectrum change at low //k//? - Why for cold dark matter does power increase at high //k//? - Draw the density vs. position for a cold dark matter density field as a function of time (nonlinear collapse). - How does the non-linear scale in real space correspond to power in k-space? - What is the evidence for deviations from the Hubble flow locally? - How about on large scales? - Can this be detected with supernovae? - How do you disentangle peculiar velocities from Hubble flow? - What does this have to do with the Kaiser effect? ===== Silverman Stars ===== **Eliot Quataert** -What is the Sun’s mass? Radius? Luminosity? Surface temperature? Central temperature? Surface density? Central density? -What’s the minimum mass of a star? Minimum radius? Minimum luminosity? -How does luminosity scale with mass (for stars more massive than the Sun)? -Derive this relationship. -What is the energy transport mechanism in different parts of Sun? -What assumptions in this derivation are not applicable for low mass stars? -What is Kramer’s opacity? What does it physically represent? -How does the central density of a low mass star compare to that of the Sun? -When we say ‘minimum mass of a star’, what do we mean? Explain the demarcation between a star and ‘not a star’. -What is the maximum mass of a star? -How is this constrained observationally? -Is mass constant as a function of time? -What is the Initial Mass Function? -What is the maximum radius of a star? What is the largest a star can be? -What is the maximum luminosity of star? What is the Eddington luminosity? What is the Eddington luminosity for a 100 solar mass star? -Do we understand what sets the maximum mass of a star? What are two processes that limit the mass of a star? -Estimate the convective velocity near the solar photosphere (surface). -What do we mean by density at the ‘surface’? -Is this velocity ‘big’ or ‘small’? -What should we compare this velocity to? -What is the sound speed at the solar surface? -How does this make modeling of the solar photosphere more complex (in a very general sense)? -Sketch an H-R diagram (and since this is Eliot, he will only accept Effective Temperature vs. Luminosity!!). -Label the main sequence. -What do we mean by the ‘main sequence’? -What are the relevant nuclear reactions? -Write out the steps of the CNO cycle. (Eliot was kidding but I was totally ready to write it out and then Eliot admitted he couldn’t remember all the steps!) -Why does the temperature dependence vary between the p-p chain and CNO cycle? -What is the Gamow energy? -What are the two competing forces involved in fusion processes and why is it a competition (//i.e.// derive their energy dependences and show that they compete against each other). -Draw the Hayashi line on the H-R diagram. -What is the Hayashi line? -When is it of interest (//i.e.// what stages of stellar evolution)? -Physically, what is the structure (//NOTE: tough to read handwriting here, I think it says ‘structure’//) of giant stars? ===== Silverman ISM ===== **James Graham** -Primary phases of the ISM in table form (CNM, WNM, WIM, HIM, Molecular Clouds). -Temperature and number density for each phase. -Which has largest volume filling factor? -What is the power source of HIM? -How do we know the CNM and WNM coexist? -How do we observe each phase? What are their tracers? What do we see from the WIM from large parts of the sky? -Why is it so difficult to observe the HIM? What absorbs the high energy photons emitted by the HIM? -How are photons emitted from NH₃? At what frequencies? What type of transition is this? -What is the emission measure and how do we observe it? (Intensity/surface brightness) -What are the collision partners? Why does Hα get emitted? (recombinations) -What is the dispersion measure and how do we observe it? What is physically happening to photons that we detect using the dispersion measure? -Perpendicular to the plane of the Milky Way we observe an emission measure of about 4 cm^-6 pc. -From this, infer the number of ionizing photons (using the recombination coefficient and the on-the-spot approximation). -What are α⁽²⁾ and the on-the-spot approximation? -Why can α⁽²⁾ be taken out of the emission measure integral? -What does α⁽²⁾ depend on? Why is the temperature constant along the line of sight? -What is the value of α⁽²⁾? -What is the number of ionizing photons per second per kpc²? (3e49) -What type of star does this correspond to? (one O5 star) -How can the CNM and WNM exist in pressure equilibrium? -Why do they have such different temperatures? -Why are there no stable phases with temperatures between that of the CNM and WNM? -What are the dominant heating and cooling mechanisms of the CNM and WNM? -Sketch the pressure-density curve for the CNM and WNM. -Label pressures, densities, temperatures, CNM and WNM, and unstable regime. -What does the kinked line represent? What about above and below the line? -What is the net cooling function (L)? How does Λ and Γ depend on the number density? (they don’t) -Use the plot and the definition of L to show that the CNM and WNM are stable while the kinked part of the curve is unstable. ===== Silverman Fluids ===== **Eugene Chiang** -Why is a magnetic dynamo hard to make in the lab? -What is the magnetic Reynolds number? -Why does it need to be large to get a dynamo? -The magnetic Reynolds number comes from what equation? -What is the magnetic Reynolds number for a ‘table top’ experiment using liquid mercury (with a magnetic diffusivity of 7000 cm²/s)? -What magnetic field geometry can cause an accretion disk to rotate significantly sub-Keplerian? HINT: In class we talked about how gas pressure could accomplish this. -Draw the magnetic field geometry that could cause this. (either magnetic pressure or magnetic tension can do it) -How large of a magnetic field is needed for magnetic tension to cause an order unity reduction in the rotation rate (from Keplerian)? -What is the plasma β? -Express the required magnetic field in terms of the sound speed and the Keplerian orbital speed. -Is the ratio of the scale height to the disk radius usually large or small in accretion disks? -With the required magnetic field, is the plasma β large or small? -With the required magnetic field, would the MRI work here? -We have a steady, spherical, γ-adiabatic wind from a star. -Is the velocity at infinity finite or infinite? -What is conserved along the wind’s streamlines? -Under what conditions is this conserved? -Is the velocity at infinity finite or infinite for an //isothermal// wind? -Imagine a disk with gas and dust where the dust can settle toward the midplane of the disk (leaving a thicker layer of gas above it). You are given the gas scale height and the surface density of the gas. -Assuming cosmic abundances, how are the surface density of the gas and dust related? -What is the thickness of the dust layer when self-gravity becomes important? In other words, how far does the dust settle toward the midplane before its self-gravity becomes important? -What is the criterion for gravitational instability for an accretion disk with self-gravity? (Toomre Q) -How are the Toomre Q and the disk with gas and dust related? (they are basically the same derivation except that the dust is pressureless) ===== Williams Cosmology ===== **Chung-Pei Ma** * What's the difference between dark matter and dark energy? * Why does dark energy not clump? * What is the equation of state, in general and in the particular case of dark energy? * How is the sound speed of a material defined? * What is \(w\) for baryons? * Is \(w\) always zero for baryons? * What is the definition of a baryon? * (After calling neutrons "long-lived.") What is the lifetime of a neutron? * What is the temperature of a typical photon at redshift 1000? * Did all the photons have an identical temperature? * Why is the redshift of 1000 interesting? * What kind of scattering was going on around that time? * Is Thompson scattering the most general form of scattering between an electron and a photon? * What is the difference between Thompson and Compton scattering? * Is Compton scattering relevant at z = 1000? * Is Compton scattering ever relevant for the CMB? * What is the S-Z effect? * Where are the hot electrons coming from? * (After mentioning intracluster medium gas falling into the cluster's potential well.) What is the typical mass of a galaxy cluster? * What are the basic properties of the CMB anisotropy? * Plot the CMB anisotropy power spectrum * What are the \(C_l\)? * Is \(C_l\) just expressing \(\Delta T/T\)? (Emphasizing the fact that the \(C_l\) show the spectrum of the two-point angular correlation function \(\langle \Delta T_1/T_1 \cdot \Delta T_2/T_2\rangle\).) * What sets the position of the first peak in the CMB power spectrum? * If the universe were open, would the peak be at a higher or lower \(l\)? * Can you relate the position of the peak to the cosmological horizon scale? * (After a lot of flailing around.) What is the speed of the baryon acoustic oscillations? * What is the most important result to come out of studies of the CMB anisotropy power spectrum? ===== Williams Star Formation ===== **Steve Stahler** - What kind of clouds are there in the Milky Way? - What is there besides molecular clouds? - What is the approximate temperature of a cloud of atomic hydrogen? - Which clouds are gravitationally bound? - What does it mean to be gravitationally bound? - Are GMCs bound? How can you tell observationally? - (After proposing a comparison of the gravitational binding energy of a clump within the cloud to its kinetic energy.) What's the average velocity of a clump within a GMC? - How can we determine this number observationally? - What is the first stage in a star's life? - What is a protostar? - How long does one typically survive? - How do we know what \dot M is? - Derive the freefall time to order of magnitude. - If the freefall time sets \dot M, why is the cloud sound speed a_T relevant (in, e.g., the expression a_T^3/G)? - What's the next stage in a star's life? - Suppose you thought you found two equal-mass PMS stars in a tight binary with one having twice the radius of the other. Why would this be an unlikely result? - If it were true, which star would be younger? - Imagine the stars are encased in Mylar and connected with a pipe so that each star's luminosity is channeled entirely to its companion. What happens? - Which star initially has a higher internal temperature? - What's the physical difference between T_{\rm eff} and T_{\rm c}? - Sketch the paths of these stars on an H-R diagram. - What's the subsequent evolution of the two stars? - What final, common radius do the two stars equilibrate to? - What is the equation for the total initial energy of each star? - What equation then holds when the stars have equilibrated? ===== Williams Radiation ===== **Eugene Chiang** - Estimate the Thompson opacity of a solar-metallicity plasma. - What's the meaning of LTE? - What is the brightness of a slab in LTE at a temperature //T// with an optical depth of \(\tau\)? - Suppose you have a plasma with relativistic electrons, threaded by a magnetic field. The distribution of electron energies is a power law. What spectrum results? - Why is the medium optically thick at low frequencies? - Sketch the optically-thick portion of the spectrum and label its slope. - What is the dependency of the spectrum on the strength of the \(\vec B\) field in the optically-thin region? - How about in the optically thick regime? - (After not knowing the answer.) Can you rederive the power law dependence of the optically-thick portion of the spectrum and hence recover the \(\vec B\) field dependence? - Sketch the synchrotron self-Compton (SSC) emission. - How much is the SSC spectrum shifted with respect to the original spectrum? - Where is the peak of the SSC spectrum? - (After a lot of flailing.) What sets the location of the peak of the original spectrum? By what value will this peak frequency be scaled in the SSC spectrum? - How high is the SSC peak compared to the synchrotron peak? - How is molecular hydrogen detected? - Why is it difficult to detect \(H_2\) through rotational transitions? - What is the approximate wavelength of the vibrational emission from \(H_2\)? - How would one estimate the effective spring constant of vibrating \(H_2\)? - What column of \(H_2\) gives an optical depth of unity in the vibrational transition? - Estimate the Einstein \(A_{21}\) of this transition. - Is this transition dipole or quadrupole? Why? - Generally, how much is quadrupole emission suppressed relative to dipole emission? ===== Bauermeister Cosmology ===== **Chung-Pei Ma** In cosmology, we talk about the linear and non-linear regimes. * What determines if you’re in the linear or non-linear regime? * Give an example of each. Talk about some important redshift milestones in the history of the universe. * Anything between z ∼ 1 and z ∼ 10? Give an example of a universe in which structure does not form hierarchically. (Answer = neutrino universe) * What controls structure formation? (Jean’s length) * What about dark matter? (zero Jean’s mass) * Hot vs. Cold Dark Matter: candidates for hot DM? * So how could you suppress small-scale structure formation? * How do you determine if something is relativistic? Talk about the history of baryons in the universe. * What happened to baryons after decoupling? * What would the amplitude of baryon fluctuations be today in a baryon-dominated universe? (Be quantitative) * Why do we think there is baryonic dark matter? * How do we get Omega_M ∼ 0.25? Without using the CMB? * The ratio of neutrons to protons determines Y - how is the baryon to photon ratio related? * Sketch a semi-quantitative plot of this effect. What is the baryonic dark matter? * How would you look for it? * If you were designing a micro-lensing experiment, where would you look? * If not MACHO’s, what else could it be? (hot gas) * How hot? ===== Bauermeister ISM ===== **Al Glassgold** High frequency photons ( ∼ UV): what processes affect their propogation? * Compare the cross-sections for these processes. (extinction by dust, photo-ionization, line absorption) * What N(HI) is needed to attenuate dust? At what wavelength? * How does attenuation depend on wavelength? * Is photo-ionization stronger or weaker? * What about line absorption? What are typical line widths observed? * How could you make your line absorption cross section smaller? What are the typical density and temperature of an HII region? * Why 10^4 K? * Why are forbidden lines relevant? * What are the typical energies for these lines? ( a few eV) * From what kind of elements? * How does gas cooling depend on temperature? * How does gas cooling depend on density? * Does the cooling rate always depend on density squared ? (No) * How does the cooling rate depend on density at very high density? * What is the critical density? What physical properties are observed for the different phases of the ISM? * Is density an independent parameter? (not if in pressure equilibrium) * Describe stability. * Explain what a photon dominated region is. * How does attenuation happen? * Give examples - what if you only had UV photons? * Common example is? (cloud in ISM not near stars) * How does the shielding go? * How far into the PDR do you have to go to get molecules? * What are the conditions for forming molecules? ===== Bauermeister Fluids ===== **Eugene Chiang** Waving my hands, is the air compressed? * How small is the compression? * How do you estimate it? Discuss an astro example where a fluid is no longer incompressible * Estimate the pressure necessary to liberate an electron from a water molecule. (Mbar) * What is the equation of state of a degenerate electron gas? * Where do we see these sorts of pressures? (gas giant planets) * Estimate the central pressure of a gas giant to check that this applies. Transport of angular momentum in accretion disks. * Give some ways of doing this. (viscoscity, turbulence, magnetic fields and the MRI) * What are the criterion for the MRI? (B not too big: mag energy density < pressure) * Is there another criterion? (didn’t know) * What dimensionless parameter determines where magnetic fields are important? (magnetic Reynolds number) * Why must flux freezing dominate for the MRI to work? * What is magnetic flux? * What are some other ways other than the MRI? * How can you form stars in a disk? (Toomre Q) * What is the meaning of Toomre’s Q? * Which kind of waves transport angular momentum? * Is Q ∼ 1 a strict criterion? Does the magnetic Reynolds number contain magnetic field? ===== McConnell Star Formation ===== **Steve Stahler** Star Formation in Galaxies - What are the three main types of galaxies? - Rank these types in order of increasing star formation rate. - What observations indicate ongoing star formation in other galaxies? - Why is H-alpha good indicator? Are O-stars bright in H-alpha? Why would we expect to see H-alpha coming from HII regions? - Rank the galaxy types from reddest to bluest. - Why are elliptical galaxies red? Observations of ISM Gas - How do we observe molecular clouds? - Are the clouds mostly composed of CO? What are they composed of? What is the relative abundance of CO? - How do we observe CO? What is physically happening to the molecule? - At what temperature is the CO transition excited? - What surrounds a molecular cloud? - How do we detect neutral hydrogen? - How did 21-cm observations help provide evidence for the existence of dark matter? Dense Cores - What do we call the clouds that form individual stars? What is their size and density? - How do we observe dense cores? How do we determine their density? - What is the definition of critical density? For the collisional term, what particles are colliding? - What can we learn from the spectra of molecular lines in dense cores? Are the line profiles dominated by natural broadening? What are other sources of broadening? - Dense core rotation curves have slopes of roughly 1 km/s per pc. What is the typical rotation period of a dense core? - It has been claimed that the observed shape of some dense cores is due to flattening by rotation. Is this reasonable, given the rotation period you determined? - What is the free-fall time of a dense core? - Given the rotation period and free-fall time you determined, by what percent would you expect the shape of the core to deviate from a sphere? Protostars - What do dense cores form next? - How do protostars differ from Main Sequence stars? - When you observe a protostar, what surface are you actually looking at? - What temperature characterizes the emission we see from protostars? - (in absence of an adequate response) Where does the protostar luminosity come from? What is the formula for the luminosity? - Suppose the radius of the observable surface is 10 AU. What is the effective temperature? Pre-Main Sequence Stars - How do pre-Main Sequence stars differ from Main Sequence stars? - Is the Main Sequence brighter or dimmer than the pre-Main Sequence? Why? - Make an HR diagram and sketch the pre-Main Sequence track of the Sun. - Sketch the track of a brown dwarf. Why does it take that track? Stellar Outflows - How do we know that young stars have winds? - What is a Herbig Haro object? - How fast do the jets move with respect to the ISM? - Given a speed of 300 km/s, estimate the temperature downstream of the shock. What type of radiation would we expect from this temperature? - We don’t actually see such high-energy radiation coming from Herbig Haro objects. Why not? - At what wavelengths do we actually see Herbig Haro objects? ===== McConnell Stars ===== **Eliot Quateart** HR Diagram and Hayashi Line - Draw the axes of the HR diagram. Add the Main Sequence and Hayashi line. - Add values to your axes. What is the effective temperature of your Hayashi line? - What physics characterizes the Hayashi line? Does the line only apply to contracting objects? - What are the masses of fully convective Main Sequence stars? - Why doesn’t the fully convective Main Sequence look like the Hayashi line? - Where is Jupiter on your HR diagram? Convection - Convection is not well understood, and simulations have only recently produced realistic results. Why has our long-standing ignorance not been a major stumbling block for modeling convective stars? - Why is the entropy gradient close to zero for convection? - Is the entropy gradient for convection always near zero? When/where might it not be? - What is the convective flux? Don’t use parameters a or d. - Why isn’t the entropy gradient close to zero near the photosphere? - (after writing r = r0 * exp(-z/H)). Is that an exact relationship? To what extent? - What is the density contrast between the photosphere and the base of the convection zone (for the Sun)? - What is true about pressure and density for an adiabatic fluid? What is the word we use for (model) stars with this relationship? - How do we calculate the luminosity for fully convective stars? Photosphere Properties - What is the photosphere? - What is optical depth? - What opacity is assumed for the Hayashi line? - Is H-minus opacity more sensitive to density or temperature? - Where does H-minus opacity come from? Why is it so temperature-sensitive? - If the Sun were fully radiative, would it have a smaller or larger radius? - (after incorrect answer) How does the pressure-density relationship change for a fully radiative fluid (vs. convective)? How does that influence the radius? Solar Observations - What are the mass, radius, and luminosity of the Sun? - What is the central temperature? Do we know this observationally? - How does the luminosity of observed solar neutrinos vary with temperature? - (after incorrect answer) What fusion method produces the neutrinos we detect at Earth? How does this kind of fusion vary with temperature? - What is another way to empirically determine the temperature near (but not all the way down to) the center of the Sun? - What is the central density of the Sun? - At what radius does the solar convection zone begin? What makes convection occur there? Low-Mass Objects - What is the minimum luminosity for (Main Sequence) stars? - What is the empirical scaling law for luminosity vs. mass on the Main Sequence (near MSun)? Radius vs. mass? - Why is there a minimum mass? - What is the central temperature of the lowest-mass stars? Effect of Fusion on Stellar Properties - Why is the statement “Fusion sets the radius of a star,” preferable to “Fusion sets the luminosity?” - Take, for instance, a star with fully radiative energy transport. What is the equation for the flux? - What is the mass-luminosity relationship for a star with fully radiative flux (assume gas pressure dominates radiation pressure)? What does this relationship look like on the HR diagram? - Why does fusion make a star stop contracting? White Dwarfs - What mass range of stars produces white dwarfs? Neutron stars? - We have observed pure helium white dwarfs. Why is this surprising? What might explain the existence of these objects? ===== McConnell Fluids ===== **Eugene Chiang** (waves hands) - When I wave my hands, how much am I compressing the air? - Derive the relationship between the compression and the velocity of my hands. Reflecting telescopes suffer “mirror seeing” due to a thermal layer that forms above the mirror surface. One can attempt to suppress this by blowing a steady air stream across the primary mirror. - Give (and justify) an expression for the thickness of the thermal boundary layer. - What is the thermal diffusivity of air? - How do we determine the value of viscosity for air? An object of mass M and radius R is embedded in an infinite medium with temperature T and density r at infinity. The object is at rest with respect to the medium. - How does the accretion luminosity scale with the given quantities? (can assume the pre-shock infall is isothermal) - Sketch the Mach number of the medium vs. the distance from the object. - How does the waveband of the accretion luminosity scale with the given quantities? (waveband ≈ peak wavelength) The MRI and Plasma Conductivity - What are the necessary conditions for the MRI to operate? - What are the expressions for Alfven speed and sound speed? - What parameter is their ratio equal to? - What happens if the magnetic field is too strong? - What restrictions are there for the rotation curve of the disk (to induce MRI)? - How do we quantify the extent to which the disk needs to be ionized? - What is the conductivity of a fully ionized plasma? - Which type of collision (electron-electron, ion-ion, or electron-ion) is important for determining conductivity? - Show how the collision frequency between electrons and ions scales with density and temperature. - Explain the form of the Coulomb cross-section between electrons and ions (temperature dependence and meaning of the “Coulomb log” term). ===== George Radiation ===== **Geoff Bower** Radiative Transfer - What is specific intensity \(I_\nu\) and why is it important? - Write the equation of radiative transfer. - Now write it in terms of optical depth \(\tau_\nu\). - Explain how spectral features are formed in stars. - What is limb darkening? Cyclotron and Synchrotron - Caclculate the cyclotron frequency. - What is the spectrum from an electron moving in a magnetic field at low energy? At high energy (\(\gamma >> 1\))? - What is the total power due to synchrotron radiation? - What is the spectrum of synchrotron radiation for a power law distribution of electron energies? Hydrogen - Draw an energy level diagram of hydrogen. - Give an order of magnitude estimate of the ground state energy. Derive the Bohr radius (Eliot). - What would the spectrum of a bright background source shining through a cloud of cold hydrogen atoms look like? How about at short wavelengths (shorter than optical)? - Besides those optical and UV lines, what additional processes produce radiation from atomic hydrogen? - What produces hyper-fine splitting? Give an order of magnitude estimate of the energy of this splitting from first principles. - What causes the Zeeman effect? ===== George Stars ===== **Eliot Quataert** Heavy Elements - Plot the solar abundance of elements versus atomic number. - Explain the peaks and dips of the plot, and describe the production mechanisms in different regimes (\(^4\)He, C/N/O, Fe, heavier). - How were the iron and nickel in the sun formed? - What happens to the iron formed in the cores of massive stars? - Nuclear statistical equilibrium; what temperatures are required to fuse heavy elements and how do you estimate this? What is different about fusion at these temperatures compared to the lighter elements? What determines whether iron or nickel is more common? Why are heavier elements more neutron-rich? Red Giants - Draw an H-R diagram with axes labeled and point out the location of red giants. - Draw and explain the trajectory through the diagram of red giants. Why are they on the Hayashi line and why are they going up it? - How does the density of the photosphere of red giants compare with that of the sun? (Compare each of the factors, \(T_{\rm eff}\), //g//, and \(\kappa\)) - Where does H\(^-\) opacity come from and why is it so temperature-sensitive? Why do you get a lower opacity at lower temperatures, and where do the electrons come from? ===== George ISM ===== **Carl Heiles** - So, what's in this big dark space (list the components of the ISM). - Pick one of them. (CNM). OK, you probably know about that one so let's talk about something else. How do we observe the HIM? - Draw an energy level diagram of OVI. - Tell me about the WIM. - How does dust heating work? - How do we observe the WIM - tell me about the surveys that provide lots of information about it (Hoyle \& Ellis in '50s, WHAM). - What are the effects of WIM on pulsar propagation? - Why are there two phases of neutral medium? Give details on two-phase diagram. - What are the heating and cooling processes in the NM? - Draw the cooling rate in the ISM as a function of temperature. - What part of the spectrum does carbon cooling appear and what upcoming much-hyped observatory may be able to observe this line in - the earliest galaxies? - How does CII heating work? ===== Shiode Stars ===== **Eliot Quataert** //Will be updated shortly// - Let's discuss the asymptotic giant branch (AGB). - Draw the AGB on an HR Diagram. - Label the axes with representative values. - What initial stellar masses eventually end up on the AGB? - Why did you draw it where you did? - What does the Hayashi line (HL) represent? - What is the relevant opacity for stars on the HL? - What does the opacity depend on? //(I said \(\rho\) and T)// - Ok, show me a plot of opacity vs. T, say, and tell me where we are for stars on the HL. - What else does the opacity depend on? //(uuhh..?)// - What is the Rosseland mean opacity? //(Oh.. right.)// - What kind of fusion is going on stars on the AGB? - How does He fusion work? How is it different from H-fusion? - How does the luminosity of AGB stars depend on the mass of the core? - Is He shell fusion always stable? When is it not, and why? - AGB stars are known to lose mass efficiently, how do they do this? - Ok, let's switch gears and talk about energy transport in stars. - Why is energy transported by radiation and not, say, electron conduction in the core of the Sun? - Estimate the electron Coulomb cross section. - When does convection become important? - What does convection do to the entropy gradient in the star? - What is the photon diffusion time in the core of the Sun? //(not sure how this got connected to the above..)// ===== Shiode ISM ===== **Al Glassgold** - Taking a "global view," //sketch// the different types of gas in the Milky Way and provide some estimates of their properties - Where are the young stars in this picture? - How does the gas pressure vary amongst the different components? - What is the force balance between the components? What are the different sources of pressure? - HII regions have typical temperatures of ~ 8000 K. How do we know this from observations, and how do we explain this in terms of thermal processes? - What's heating and what's cooling? - Why isn't recombination cooling sufficient? - Write down an expression for recombination cooling. //(I couldn't..)// - What kind of spectrum do you get on recombination? - Aside from emission lines, what else? - What about line cooling? - What are forbidden lines? How much cooling do they provide? - What's molecular about Giant Molecular Clouds? - Properties (size, density, temperature?) - How are they observed? (what wavelengths, etc.) - What kind of spectra do molecules produce? Let's focus on CO. //(because I said it)// - What kinds of lines do you get from CO? Draw the energy levels of CO. - Which lines are important in GMCs? - Are vibrational transitions relevant? Why/why not? //(I said vibrational.. foot-in-mouth..)// - What temperatures do vibrational transitions correspond to? - What are the major constituent molecular species? - What other molecules are observed besides CO? Where is the N? - How much NH\(_3\) is there in clouds? O? O\(_2\)? H\(_2\)O? //(Uhh..?)// - Why isn't H\(_2\) observed? - How do we calculate the masses of GMCs? - Name one way to convert from CO luminosity to H\(_2\) mass. ===== Shiode Fluids ===== **Eugene Chiang** //Absolutely no preparatory remarks.. First words out of his mouth: // - What is magnetic braking? - Give an expression for the spindown time. //(..mild panic..)// - What is the spindown time for a non-magnetized wind? - Ok, what's different for a magnetized wind? - Given \(n, v_w, B_r\) at 1 AU in the solar wind, estimate the location of the Alfven point. //(..more panic..)// - Ok, you've remembered \(B_r \propto r^{-2}\), what about \(B_{\phi}(r)\) outside the Alfven point? - Show mathematically that \(B_{\phi} \propto r^{-1}\) for \(r > r_A\). //(..uuuuuummm...?)// - What is flux-freezing? //(OH YEA!...wait..)// - (~ 30 minutes later..) Let's talk about accretion disks. - What are some popular ideas for how accretion disks work? List the ones you know. - What's the Jeans Mass? Estimate it in terms of \(\rho\) and \(c_s\) - If a Jeans Mass collapses, does it continue? - What is the role of increased T? - What is the condition on \(\gamma\)? - Under what conditions do trailing spiral density waves develop? - What is Toomre Q? How does it relate to the stability of gas in a disk? - Why is Q = 1 a "magic number"? Where does that come from? - What does this have to do with accretion? ===== Viscomi Cosmology ===== **Martin White** What observational evidence would you require to make you disbelieve a hot big bang? - What problems with the CMB might be important? - Why is the CMB expected to be such a good black body? - What would be the impact of a very massive neutrino? - What would Omega_neutrino be? - How do you estimate the age of the Universe with Omega > 1? How many degrees of freedom are in a Friedmann model? - What is k? - How many types of universes are there? What are they? - How do you know if the universe is flat? - How do you know this from the first peak of the CMB? - What is the redshift of the CMB? - What is the distance to that redshift? - How would being in a closed universe affect the angular diameter distance to that redshift? - How does density affect evolution of scale factor? How well do we know each parameter in the Friedmann model? - What are the uncertainties in the best known values of each Omega? - If the supernova results are proved wrong, how well do we know Omega_Lambda? - Was the discovery of dark energy expected? - Can you give an argument for using lambda before the supernova discoveries? - What is the physical source of dark energy? - What is interesting about omega matter? - Where are the baryons today? at high redshift? - What is interesting about the values of Omega_Lambda and Omega_matter? Is the balance between them explainable? ===== Viscomi Stars ===== **Eliot Quateart** - What is the main sequence transition mass between WD and NS? - What observations give must this value? - How can we find out about the MS mass of a star before supernova? - Draw an HR diagram for a star cluster. - Where does most mass loss occur? - What is the radius, temperature, and luminosity of a red giant? - Why is evidence for an isolated He WD surpising? - What is the MS lifetime of a 1/2 solar mass star? - How could a He WD be formed in a binary? - What is the difference between the AGB and the RGB? - Where does the Hayashi line come from? - What opacity is important on the line? - Why does it have such a strong temperature dependence? - Why does lots of mass loss occur in the AGB phase? - Why is this different for the CNO cycle in massive stars? - Explain the thin shell instability. - What is the helium flash? ===== Viscomi Radiation ===== **Geoff Bower** Radiative Transfer - What is intensity? - Why is it useful? - What is the equation of Radiation Transfer? - What is optical depth? - How do absorption lines get formed in stars? - How are emission lines formed? - What part of a star do emission lines come from? - Explain limb darkening? Synchrotron - Calculate the cyclotron frequency. - Draw a cyclotron spectrum. - What is the difference between cyclotron and synchrotron radiation? - Draw the synchrotron spectrum of a single emitter. - Derive the total power radiated by a single synchrotron emitter. - Draw the spectrum of a power law distribution of electrons. - Why is there a low frequency cutoff? How does it depend on frequency? Why is it different from the RJ tail? Atomic Energy Levels - Diagram the energy levels for hydrogen. - What sets the energy scale? - What are the important transitions for hydrogen? - What is the impact of an O star shining on an H cloud? What is the spectrum of the cloud? - When will the gas be transparent to bound free transitions? ===== Pober Radiation ===== **Geoff Bower** - Given three spectra, identify the components and what they are. (All three had synchrotron and thermal). - Consider the synchrotron component. - What does the power law say about the source? - Extrapolate to lower frequency – what do you expect? - What are the other properties of the radiation? - What kind of polarization do you expect? - Describe it. - If the source had an ordered magnetic field pointing toward you, what do you expect for the polarization? - Consider the thermal component. - What's the temperature? What's the wavelength at which it is emitted? - What part of the electromagnetic spectrum does this correspond to? - What do you expect this originates from? - What can you measure from the given spectrum to know whether its a blackbody? - What would you conclude if the frequency dependence is \(\nu^3\) instead of \(\nu^2\)? - Molecular transitions from dipoles. - What are the transitions from molecules? - Give order of magnitude estimates for the energy levels. - How do the level spacings change depending on the transition? - If J=1-0 is at 115GHz, where is J=2-1? ===== Pober Galaxies ===== **Leo Blitz** - Measuring the deuterium abundance at z=0. - Where in the Milky Way would you look? - Is all gas in stellar atmospheres processed? - What is the D/H ration at z ~ a few? - Where is the most unprocessed gas in the MW? - Where is the most column density per frequency interval? - What is the observed radial velocity of gas in the MW vs l, b? - How do chemical abundances change with time? - What is the difference between Type I and Type II supernova? - What is the G dwarf problem and what is the closed box model? - What is the cooling time for gas? - Estimate the cooling time in the IGM. - How does limit the density of the IGM? - What is the SZ effect? (Thermal and kinetic) - Is this gas easier to see in radio/sub-mm or X-ray? - What is the distance dependence? - Order of magnitude values. - How big is a disk galaxy? - What is dN/dM for galaxies? - What is the surface density of stars in the Galaxy? - What is the mass-to-light ratio of: - The Milky Way - The Milky Way disk - Ultra-faint dwarf galaxies - What is the mass of the bulge? - How many galaxies are there in a rich cluster? - How many galaxies in a group? - What is the scale height of the disk? ===== Pober Cosmology ===== **Martin White** - What is the baryon density? - How do I know that? - What if the baryon density goes up and the 3rd CMB peak goes down? - How else do we know the baryon density? - How does nucleosynthesis depend on temperature? - Does it make sense that \(\Gamma\) falls faster than H as a function of T? - Are there other elements produced in BBN? - What is the source of the \(^7<\)Li dip? - How do you measure abundances of these elements? - At what redshift can you measure deuterium abundance? - At what redshift does nucleosynthesis take place? - Why is it OK to use the low redshift deuterium for this? - How could BBN be changed? - What happens when we change the chemical potential of neutrinos? - What might alter the CMB power spectrum? - How much energy density of the early Universe is in dark energy? - What about modifying gravity or introducing new particles? - What else composes \(\Omega_m\)? - Where is most of the baryon mass? - What physical conditions permit us to hide baryons in the IGM? What is a rough guess of the IGM temperature? ===== McCourt Stars ===== **Eliot Quataert** Masses of stars. - What is \(M_{\odot}\) in g? - What is the mass range of stars? Is this observationally or theoretically determined? - Explain the high mass cutoff. What makes high mass stars so weakly bound? Why doesn't this apply to lower mass stars? - What is the luminosity for the highest mass stars? - What assumptions went into your derivation? What is the source of the opacity? - How does this change for the interior of the star? - Explain the low mass cutoff. What is the status this transition,observationally and theoretically. - Derive equations for the central pressure and temperature of a star. What distinguishes stars from non-stars? - Draw an HR diagram, and sketch a low-mass, pre main sequence track. - What is it called? What important assumptions go into the Hayashi track? Why is the \(H^-\) opacity so temperature sensitive? - How does the radius depend on mass for this object? How does it compare to Jupiter? - What other physics becomes important as you decrease the mass? - What happens if you go to zero metallicity? - Does the mimimum mass change dramatically? - How about the maximum mass? - What is the source of fusion for a \(100 M_{\odot}\) star? Does this change if there is no metallicity? Explain the evolution of the star. ===== McCourt Radiation ===== **Geoff Bower** (Shows a plot of the spectrum of a galaxy). - What are the sources of emission? (There was a power-law spectrum in the radio which I said was probably synchrotron and a Planck-ish spectrum in the IR, which I said was probably dust). Synchrotron - What happens to the synchrotron spectrum at lower frequencies? Why does it not look like \(\nu^2\)? - What is the spectrum of particles which produce this emission? What is the observed range of power-law indices? What is the observed range of particle energies? -What can you learn about the magnetic field from the synchrotron emission? How does the flux depend on //B//? What does the polarization tell us? Thermal Emission -What can you learn from this plot? - What is the temperature of the source of this emission? What in a galaxy can have this temperature? - Explain the shape of the Rayleigh-Jeans tail. Why is it steeper than \(\nu^2\)? - What part of the spectrum is this? Name a satellite which can observe this. Molecular Spectroscopy - What kinds of transitions do dipole molecules make? What are the relative energies of these processes and in what wavelengths do they appear? - What are the selection rules for each process? What do the spectra look like? - You found that the vibrational spectrum should only show a single frequency. In fact, there is a forest of lines. How do you explain this discrepancy? - Estimate the energy of vibrational transitions. Also rotational transitions. - What are the most important rotational transitions? ===== McCourt Cosmology ===== **Martin White** Recently there have been some rumors about an upcoming result from the CDMS experiment. - What is the CDMS experiment looking for? What is a dark matter particle? - Explain the evidence for dark matter in clusters. How about in galaxies? - How big is the local dark matter density? (I stumbled a bit on this one so Martin had to walk me through it) - What dark matter density profile would produce a flat rotation curve? - What is the rotation speed in our galaxy? - What is the outer radius of mass in our galaxy? Is the Milky Way a typical galaxy? - How does the density you got compare the the average dark matter density in the universe? Clusters - What is a typical velocity dispersion for galaxies in a cluster? - Why don't we just say that gravity is wrong on large scales? Why do we need dark matter? - How well known is the matter density of the universe? What sets the error? How can you measure this using the turnover in the matter power spectrum? What assumption goes into that argument? - What is the cosmic neutrino temperature? - How can you measure the matter density from the CMB? ===== Hull Radiation ===== **Geoff Bower** Origin of radiation - What is a general requirement for radiation to be launched? - Why does the electric field of an accelerating charge fall off with distance as 1/r (as opposed to \(r^{-2}\) for a static charge)? Image interpretation - Interpret a 3.8 micron image of the BN-KL region in Orion, which shows a pattern of polarization vectors that make more-or-less concentric circles around the presumed location of the source. - What is the Davis-Greenstein effect? - How does it create polarization? - How does scattering by dust produce polarization? Thomson scattering - Derive the formula for the Thomson scattering cross section - What is its numerical value? - Over what distance, in a medium with an electron density of cm\(^{-3}\), is Thomson scattering significant? Magnetic fields - Name three different ways to measure an interstellar magnetic field - Explain the rotation measure of an ionized medium - In practice, how is this used to find the magnetic field? Random - What are the Stokes parameters and what do they signify? ===== Hull Galaxies ===== **Leo Blitz** Galaxies and rotation curves - What is a galaxy? - How is a galaxy different from a cluster of stars? - What if it doesn't have a rotation curve? - How do you measure the dark matter content of a galaxy? - Derive an equation for the isovelocity contours for solid-body rotation - Do spiral galaxies rotate like a solid body? - Does the bulge? - What is the requirement for Keplerian rotation? - Write down an equation for the surface density of a disk - Does the mass converge? - What is the equational dependence of the circular-velocity fall-off at large radii in the disk? Galactic mass distribution - What is the Local Group? - What is the most common type of galaxy? - Why are these galaxies hard to see? - What are the highest mass galaxies? - What is the mass distribution of the Local Volume? - What is the Schechter function? - At what mass is most of the mass of galaxies? - Where on the Schechter function does the Milky Way lie? - Why are there more cD galaxies than we might expect? - What is the Tully-Fisher diagram? - Which line do you use to get the T-F diagram? - How do you get the absolute magnitude of the galaxies? - Why is there such a tight relationship between absolute magnitude and line width? ===== Hull Star Formation ===== **Steve Stahler** Molecular clouds - What is a molecular cloud? - How do we observe molecular clouds? - What types of molecular clouds do we see? - What are their sizes and masses? - You observe two clumps in a GMC with sizes \(L_1\), and \(L_2 = 2L_1\) - What is the velocity dispersion of clump 2 compared with clump 1? - What is Larson's Law? - How do the densities of the clumps compare? - What do we mean by visual extinction in a cloud? - What causes it? - What is the typical \(A_v\) in a clump? - What is \(A_v\) in a dense core? - How do the extinctions in the two clumps compare? - Does this make sense? - What assumption were we making that applies generally in GMC's, but not in dense cores? Bondi accretion - Suppose a star is in a cloud. Derive M_dot onto the star as it sits in a sea of gas. - What is the difference between this expression and the mass accretion rate onto a protostar (\(\frac{a^3}{G}\))? HR diagram - What does the HR diagram look like for a T association? - Assume the cluster is 10 Myr old. Where are the stars on the HR diagram? - What is the Kelvin-Helmholtz time? - What is the Kelvin-Helmholtz time of the Sun? - Why can you use the present radius and luminosity to find the K-H time when you know that the previous radius and luminosity were much larger? - Why does the K-H time get longer as you get nearer to the main sequence? - Is the time to get to the main sequence longer or shorter for a star of \(0.5M_{\odot}\)? - By how much? ===== McBride Radiation ===== **Geoff Bower** 1. Dispersion - (shows a plot of a dispersed pulse, specifically the Lorimer burst) What is happening in this plot? - What is a name for the amount of dispersion? What units are commonly used? - What is the dispersion relation? - Write this in terms of the plasma frequency. - What happens when the frequency is less than the plasma frequency? What is an example of this that is relevant on Earth? - Derive the dispersion measure from the dispersion relation. (I hesitated, and then he asked me to write down how fast a wave travels.) - What does the group velocity represent? - What happens to this when an electron is relativistic? 2. Brightness Temperature - What is brightness temperature? - How does brightness temperature relate to the kinetic temperature? - What is the equation of transfer in terms of the brightness temperature? - (Carl asked) What happens when there is negative absorption? What is an example of this? - What is a typical brightness temperature for a radio galaxy? What is the upper limit to this value? Why? - If a radio galaxy has a brightness temperature of 10^6 K, why doesn't the telescope melt? - What happens if we look at the Sun with a telescope? - (Eliot asked) How do solar astronomers look at the Sun then? - What is the difference between looking at the Sun in optical light and a radio galaxy? (Or, why does one melt and not the other) - Say you want to burn a piece of paper. What size magnifying lens would you need? (Geoff and Carl disagreed on the answer to this question, and concluded that a mirror should be used rather than a magnifying lens.) ===== McBride Stars ===== **Eliot Quataert** 1. What function describes the mass distribution of stars in the Galaxy? - Which stars account for the majority of the mass? - Which stars account for the majority of the light? - How does luminosity scale with mass? 2. What is the Eddington luminosity? Give a derivation, focusing on the star's interior rather than the surface. 3. Where in stars does convection occur? - What conditions are required in a star for it to be stable to convection? - Why does a positive entropy gradient lead to stability? - In thermodynamic relations of that sort, there is some quantity held constant. What is that in this case? (I had mentioned ds/drho in my answer to (b)). - In what sense is pressure constant? - What physical conditions apply in a convective blob? - How does the speed of sound compare to the speed of a convective blob? (I fumbled the question about constant pressure a bit.) 4. Imagine that a star is born composed of helium rather than hydrogen. - In a helium fusing star, what is the reaction that produces energy? - At what temperature does this become important? - What physics determines this temperature? - How does helium fusion differ from hydrogen fusion? (I think I asked for clarification here, considering the next question) - Write down the Virial theorem. (So I was supposed to say something about mean molecular weight for (d)) - How does the luminosity scale for a star composed of helium? - How does the luminosity of a horizontal branch star compare to a star on the hydrogen main sequence for the same mass? - Start with a one solar mass pressureless gas cloud composed of helium and let it contract. Does it become a star? - What is the role of degeneracy pressure? ===== McBride ISM ===== **Carl Heiles** 1. What are the phases of the ISM? 2. Estimate the dispersion measure of each phase, looking out of the plane of the galaxy. - What is the scale height of each phase? - What is the temperature of each phase? - What is the number density of each phase? - What is the electron number density of each phase? - What are the modes of ionization? - What is the dispersion measure of the Crab Pulsar? (I answered incorrectly, and was told the correct value.) - What distance does this imply for the Crab Nebula? (I answer, and then note that this is much too low.) What went wrong? (Hmm.) - What is the visual extinction for your CNM column density? - How does this compare to a typical clump? (Much too large.) - What did you leave out? (Filling factor) - Estimate the filling factors. 3. Draw a picture of how the phases fit togeter. - What happens when a SN goes off? - What happens to the WIM in a star cluster? 4. Lets talk about dust. - What produces extinction? What about reddening? - What is the difference between extinction and absorption? - What are the wavelength dependences? - What are some other observational effects? - What about astrophysical effects? - Where is it important for heating? Where is it important for cooling? How? - What role does dust play in molecular clouds? - How does molecular hydrogen form on a dust grain? ===== Lee Stellar Interiors ===== **Eliot Quataert** * White Dwarfs - Can you draw an HR diagram with representative values? - Identify the main sequence and the location of white dwarfs. - What determines where they are on this diagram? - People have tried to use white dwarfs to date the age of the Galaxy. How might they do this? * Hint: Where would newly made white dwarfs be on the HR diagram? What about the older ones? - The Chandrasekhar mass depends on what parameters? - How does it depend on the chemical composition? - What is the physical origin of the Chandra mass? - How does radius change with mass in a non-relativistic white dwarf? What happens as M goes to zero? - Does this actually happen as you go to lower masses? Sketch what the true dependence looks like. - What supports a Jupiter-sized object in addition to ideal gas pressure? * Opacity - What defines the photosphere of a star? - What is the scale height of the photosphere region of the Sun? - What is the gas pressure at the photosphere? Sketch where the expression you wrote down comes from. - What is the dominant source of opacity in the atmosphere of an O star? - What about for the Sun? - During what phase(s?) of evolution is the Hayashi line important? - What is different about the AGB phase compared to the RG phase? * Helium Fusion - What reactions are involve in helium fusion? - What is special about the first step of this reaction? - What about the second step? * Hint: Is there anything special about the newly formed carbon? - Why can we use Saha-equation-like arguments for helium fusion but not for hydrogen fusion? ===== Lee ISM ===== **Carl Heiles** * Supernovae - //"So, you seem to know a lot about stars..."// Why are they important for the ISM? - What are the different phases of a supernova remnant? - Derive R(t) for the shock during the Sedov phase (//"using freshmen physics"//). - What changes across the shock? - What energy powers the shock? - What is a typical velocity of the shock? - What are typical post shock temperatures? Estimate this to order of magnitude. - What drives the shock during the other stages? Can you write down the relevant equation of motion? - What determines when the shock transitions from the Sedov solution to the pressure-driven phase? * The Hot Ionized Medium - (//"Quickly..."//) Make a table of the various phases of the ISM. Make a column for number density, temperature, and pressure. - What about the pressure of cosmic rays and magnetic fields? What is the equation for the magnetic field pressure? - What heats the HIM? What cools it? - How does the dust survive? (//Not sure we ever reached a consensus on this question...//) - How can you observationally assess the existence of dust in the HIM? * Hint: What wavelengths are prominent from the HIM gas? What are typical wavelengths from dust? - What produces X-rays in the HIM? - Would you expect OVI to be the most dominant specie of oxygen in 10^6 gas? ===== Lee Fluids ===== **Steve Stahler** * Fluids - Under what conditions can we use the fluid equations? - Can we use the fluid equations to understand the Sun? - For a one parsec cloud with a density of 1000 particles per cubic centimeter, calculate the mean free path. - Can we use the fluid equations to understand the solar wind? * (//from Aaron: Using this above procedure, no. In reality we can get away with it since the mean free path is greatly reduced because of magnetic fields. If ions are locked to field lines, the relevant length scale to consider is the gyration radius.//) - Why can we say that subsonic flows are quasi-incompressible? That is, can you estimate how density perturbations depend on the velocity of the fluid? * Isothermal Spheres - What is the free-fall time? Derive an approximate expression for it. - What is the free-fall time for the Sun? The Sun is obviously not collapsing, so what other phenomena occur on this timescale? - Plot the mass of an isothermal sphere versus internal density. Assume thermal pressure and gravity are the only forces and the sphere is embedded in a uniform density environment. - What happens to the modes at the turnarounds? In particular what is going on at the first turnaround? - What do magnetic fields do to the above? Can you write out Euler's equation with the inclusion of magnetic fields? (//I wrote the j-cross-B term in terms of B and its derivatives.//) - Talk me through how you got the Lorenz force term in the form you have written. * Circumstellar Disks - Was the disk in which the solar system formed thick or thin? - Estimate the aspect ratio (vertical scale height / cylindrical radius) at 1 AU. Ignore the gravity of the disk. - Estimate when the disk's self gravity becomes important. - How does this relate to the Toomre Q criterion? ===== Morgan Stars ===== **Eliot Quataert** - Plot the binding energy of atomic nuclei as a function of atomic number. What are the units on the ordinate? - From this, Estimate the lifetime of the sun. - What fraction of the Sun's mass is used in fusion and why? - Is the roughly 10% a fraction true for all stars? How about a 0.1 \(M_\odot\) star? How about a 100 \(M_\odot\) star? - Why does convection occur in the core of a 100 \(M_\odot\) star but not in a 1 \(M_\odot\) star? - How does the opacity depend on density? What opacity processes depend on the density? - Why is the temperature gradient steeper in a massive star? Why is the flux higher? - What are the primary energy generation mechanisms? - How does the binding energy curve tell you about the end states of stars? - When do massive stars collapse? How much iron is there in the core? Mass? - What is an important source of pressure in the star's core? - What are the implications of the binding energy curve for other types of supernovae? - How is radioactive nickel produced? - What is nuclear statistical equilibrium? What is in equilibrium? - How high are the temperatures in the stars center, and what is the typical energy of a photon? - What is the end state of fusion when in NSE? - What processes change the number of neutrons in a star? - What is special about a C-O white dwarf so that nickel (rather than iron) is produced? Similarly ,for the layers surrounding the iron core? - What is the dependence of stellar lifetimes on mass? - Where does \(L \propto M^{3.5}\) come from? - Why doesn't fusion make a difference to this? What does fusion do? - How much does the central temperature vary among stars? - Sketch an HR Diagram - What would the H-R Diagram of a 10 billion year old star cluster look like? Explain. - What else is there besides the lower main sequence and the subgiants? - What's special about 3000K? - For what stages of stellar evolution is the Hayashi Track relevant? - What are blue stragglers? What might be their physical origin? ===== Morgan Radiation ===== **Geoff Bower** (shows a plot of radio data with frequency versus time) - What is this plot describing? - What gives rise to the time delay? What is needed? - What is Dispersion Measure? What does it tell us? - Describe qualitatively how time delay is a function of frequency. - What are the typical units for dispersion measure? - What is DM used for? Typical density of ISM? - Where does the physics of DM come from? - What do \(v_{group}\) and \(v_{phase}\) mean? How do we calculate \(v_g\)? - write dispersion relation in terms of \(\omega_p\) and \(\omega\) - What are the two regimes of the dispersion relation? \(\omega < \omega_p\)? - Can you think of examples in each of these regimes? - What are some key assumptions for dispersion relation for plasma frequency? - What about radio waves propagating through relativistic plasma? - What is the SZ effect? (shows a plot of IR polarization) - What is this plot telling us? - What is causing the continuum emission? - What is causing the polarization pattern? - Why does Thompson Scattering produce polarized light? - How can you distinguish between polarization by dust and polarization by free electrons? ===== Morgan Cosmology ===== **Alex Filippenko** - Give evidence for the Big Bang Theory - Tell me about the CMB - Could it be from any other process? Iron fillings permeating throughout the universe? - Would the temperature differ with the age of the universe? - Why was the Universe oscillating? Why doesn't perturbation continue? What is opposing gravity? - What is typical scale of these fluctuations? - What dictated the size? Calculate the angular size today. - How much has the universe expanded between then and now? - Draw the CMB Power spectrum - Which peaks are compression or rarefaction? - Why does it die off at small angular scales? - Direct evidence for hotter CMB in the past? - Another piece of evidence fo the Big Bang? - Physical effects of propagating through universe - Tell me about the abundance of elements and Big Bang Nucleosynthesis - Comment on the timescales of neutron decay and the formation of light elements - Why is He 25% of the Universe? - Is the Standard BB model in good shape? - Tell me about flatness - Over what angular scales is the universe causally connected? How do we get around these problems? - Will we every know the curvature for sure? - What does the universe consist of? Evidence for each of these? - Couldn't DM be distributed broadly? - What is the integrated Sachs-Wolfe effect? - What is dark matter? - How do you find it? ===== Klein Galaxies ===== **Leo Blitz** * Galaxy Definition, leads into Dark Matter - What is a galaxy? - How does this differ from a star cluster? - How do you know about non-luminous matter? * Mass-to-Light Ratio - How do you get mass of stars? M/L ratio? - What kind of instrument would you use to measure L? - How do you get M? - Is MW M/L a good assumption - What about dwarf spheroidal? - How do you know there is dark matter? * A little on Stellar Dynamics - How do you measure escape velocity? - Could we use gas velocity? - How do you define radius for dS or dE? - Mass of spiral galaxies? - Why not go to zero intensity of HI? - Where is DM located in a spiral galaxy? - How do we know there isn't DM overdensity in disk? - Write down Poisson's equation in cylindrical coordinates. What stars do you use? - K dwarfs or K giants? * Example of observational approach to Dark Matter - What are MACHOs? - Why did we think they exist? - How much more DM than LM? - Could it have been gas? - How did we rule out MACHOs? - Weak or strong lensing? Microlensing? -- First Attempt - How do you know the MW is a galaxy? - What is a galaxy? - What kind is it? - Explain Oort constants? LSR? - How does this depend on spectral type? - What kind of stars do you use to measure Oort constants? - How do you know the MW is not unique? - Tully-Fisher relation; what is it? - What spectral line? - How does HI extent compare to starlight? - What does HI width measure? - Why was this important? - What is the Schechter Function? - Units? - What is functional form? - Where is most of the mass? ===== Klein Radiation ===== **Geoff Bower** * Dispersion Relation stuff - What is dispersion measure? Why is it important? Units? - Can the delay in frequency be expressed analytically? - What is the dispersion relation for a wave traveling through a plasma? - What happens when \(\omega\) < \(\omega_{p}\)? - What is the definition of the group velocity, given a dispersion relation \(\omega(k)\)? - What is the phase velocity, given a dispersion relation? - What is the physical origin of the plasma dispersion relation? - If the plasma's electrons are relativistic, what happens to the degree of dispersion? * Brightness Temperature and Radiative Transfer - What is Brightness Temperature? - Is it ever true, for a blackbody, that the brightness temperature is not equal to the physical temperature? - Write the radiative transfer equation in terms of temperature an optical depth. What is its equation in two limiting regimes? -- First Attempt * Radiation from charges - How is radiation launched? - Why do accelerated charges emit radiation? Why not stationary charges? - What is the Poynting vector? - How does the E field fall off with distance from a radiating charge? - How does this falloff differ from the electrostatic case? * Interpreting a polarization map - Given a polarization map, what is causing the polarization? (Shows map of star cluster with MidIR continuum.) - Generally, what can produce concentric rings of polarization vectors? - How does scattering create polarization? * Misc. Questions - Calculate the Thomson scattering cross section. Write it in terms of the classical electron radius - with derivation. - What is the Eddington Luminosity? - How is B field measured from Faraday rotation? - What is Zeeman splitting and how does it work? ===== Klein Star Formation ===== **Steve Stahler** - Sketch a pre-main sequence track for a 2 \(M_\odot\) star. - Where are two radiative stars of the same mass but different radii? - Which is hotter on the inside? Which has higher central pressure? By what factors? What about surface temperatures? - How can you tell how old the group is for a group of stars? - Sketch this on an H-R digram. Do all stars in the cluster have to be on the MS? - What are infrared classes? - What are Herbig-Haro objects? - What kind of stars drive them? - What causes the shocks that make them visible? - What's a typical velocity of an H-H object? - What's the temperature of the related shock? - What kind of radiator do you see? - What if central star as a molecular outflow? - What's the temperature in the molecular outflow? - What's more common, jets or molecular outflows as far as what is seen? -- First Attempt - Do we detect magnetic fields in star forming clouds? - How is it measured? - What's the ratio of magnetic fields in two clumps of different sizes? Derive. - What are some scaling relations for three fields in molecular clouds? - Are velocities sonic? Why don't they shock? - What is the relation between the \(\sigma_v\) of the two clumps? - What are Larson's Laws? Why doesn't it apply to dense cores? - What is an SED? - Say \(\rm{T}_{\rm{disk}} \sim r^{-8}\), what is the form of the SED for such a disk? Assume it is optically thick. - What is a passive disk? What is an active disk? - What is the \(q\) for a passive disk? (\(q\) was defined in the question about SEDs as the exponential factor describing the SED.) ===== Morgan Stars ===== **Eliot Quataert** - Plot the binding energy of atomic nuclei as a function of atomic number. What are the units on the ordinate? - From this, Estimate the lifetime of the sun. - What fraction of the Sun's mass is used in fusion and why? - Is the roughly 10% a fraction true for all stars? How about a 0.1 \(M_\odot\) star? How about a 100 \(M_\odot\) star? - Why does convection occur in the core of a 100 \(M_\odot\) star but not in a 1 \(M_\odot\) star? - How does the opacity depend on density? What opacity processes depend on the density? - Why is the temperature gradient steeper in a massive star? Why is the flux higher? - What are the primary energy generation mechanisms? - How does the binding energy curve tell you about the end states of stars? - When do massive stars collapse? How much iron is there in the core? Mass? - What is an important source of pressure in the star's core? - What are the implications of the binding energy curve for other types of supernovae? - How is radioactive nickel produced? - What is nuclear statistical equilibrium? What is in equilibrium? - How high are the temperatures in the stars center, and what is the typical energy of a photon? - What is the end state of fusion when in NSE? - What processes change the number of neutrons in a star? - What is special about a C-O white dwarf so that nickel (rather than iron) is produced? Similarly ,for the layers surrounding the iron core? - What is the dependence of stellar lifetimes on mass? - Where does \(L \propto M^{3.5}\) come from? - Why doesn't fusion make a difference to this? What does fusion do? - How much does the central temperature vary among stars? - Sketch an HR Diagram - What would the H-R Diagram of a 10 billion year old star cluster look like? Explain. - What else is there besides the lower main sequence and the subgiants? - What's special about 3000K? - For what stages of stellar evolution is the Hayashi Track relevant? - What are blue stragglers? What might be their physical origin? ===== Morgan Radiation ===== **Geoff Bower** (shows a plot of radio data with frequency versus time) - What is this plot describing? - What gives rise to the time delay? What is needed? - What is Dispersion Measure? What does it tell us? - Describe qualitatively how time delay is a function of frequency. - What are the typical units for dispersion measure? - What is DM used for? Typical density of ISM? - Where does the physics of DM come from? - What do \(v_{group}\) and \(v_{phase}\) mean? How do we calculate \(v_g\)? - write dispersion relation in terms of \(\omega_p\) and \(\omega\) - What are the two regimes of the dispersion relation? \(\omega < \omega_p\)? - Can you think of examples in each of these regimes? - What are some key assumptions for dispersion relation for plasma frequency? - What about radio waves propagating through relativistic plasma? - What is the SZ effect? (shows a plot of IR polarization) - What is this plot telling us? - What is causing the continuum emission? - What is causing the polarization pattern? - Why does Thompson Scattering produce polarized light? - How can you distinguish between polarization by dust and polarization by free electrons? ===== Morgan Cosmology ===== **Alex Filippenko** - Give evidence for the Big Bang Theory - Tell me about the CMB - Could it be from any other process? Iron fillings permeating throughout the universe? - Would the temperature differ with the age of the universe? - Why was the Universe oscillating? Why doesn't perturbation continue? What is opposing gravity? - What is typical scale of these fluctuations? - What dictated the size? Calculate the angular size today. - How much has the universe expanded between then and now? - Draw the CMB Power spectrum - Which peaks are compression or rarefaction? - Why does it die off at small angular scales? - Direct evidence for hotter CMB in the past? - Another piece of evidence fo the Big Bang? - Physical effects of propagating through universe - Tell me about the abundance of elements and Big Bang Nucleosynthesis - Comment on the timescales of neutron decay and the formation of light elements - Why is He 25% of the Universe? - Is the Standard BB model in good shape? - Tell me about flatness - Over what angular scales is the universe causally connected? How do we get around these problems? - Will we every know the curvature for sure? - What does the universe consist of? Evidence for each of these? - Couldn't DM be distributed broadly? - What is the integrated Sachs-Wolfe effect? - What is dark matter? - How do you find it? ===== Klein Galaxies ===== **Leo Blitz** * Galaxy Definition, leads into Dark Matter - What is a galaxy? - How does this differ from a star cluster? - How do you know about non-luminous matter? * Mass-to-Light Ratio - How do you get mass of stars? M/L ratio? - What kind of instrument would you use to measure L? - How do you get M? - Is MW M/L a good assumption - What about dwarf spheroidal? - How do you know there is dark matter? * A little on Stellar Dynamics - How do you measure escape velocity? - Could we use gas velocity? - How do you define radius for dS or dE? - Mass of spiral galaxies? - Why not go to zero intensity of HI? - Where is DM located in a spiral galaxy? - How do we know there isn't DM overdensity in disk? - Write down Poisson's equation in cylindrical coordinates. What stars do you use? - K dwarfs or K giants? * Example of observational approach to Dark Matter - What are MACHOs? - Why did we think they exist? - How much more DM than LM? - Could it have been gas? - How did we rule out MACHOs? - Weak or strong lensing? Microlensing? -- First Attempt - How do you know the MW is a galaxy? - What is a galaxy? - What kind is it? - Explain Oort constants? LSR? - How does this depend on spectral type? - What kind of stars do you use to measure Oort constants? - How do you know the MW is not unique? - Tully-Fisher relation; what is it? - What spectral line? - How does HI extent compare to starlight? - What does HI width measure? - Why was this important? - What is the Schechter Function? - Units? - What is functional form? - Where is most of the mass? ===== Petigura Stars ===== **Eliot Quataert** - Sketch the HR diagram. - Consider a 10 Gyr globular cluster. What would its HR diagram look like? - Describe the high luminosity part. - Physically, what is the star doing during the red giant phase. - Why does the core contract - What is the Kelvin-Helmholtz timescale for the sun. - Sometimes stars are seen above and to the left of the main sequence turnoff. What are these? - Describe stars on the Hayashi line. - What is a polytrope? - Why is \( P \propto \rho^\frac{5}{3} \) a good approximation for fully convective stars. - Why is the entropy roughly constant. - Write down the dimensionless entropy gradient. - What is the convective velocity for the sun? - Why does the entropy gradient matter? What does it have to do with buoyancy? - Why is the adiabatic approximation good? - How long does it take for energy to leak out of the sun? - Where does the entropy gradient come in. //Didn't know the answer. We moved on.// - What is the range of stellar masses we observe in the universe? - People talk about extremely massive stars in the early universe. How are these possible. - What is the IMF? - How could a massive star lose mass. //Said something about exceeding the Eddington Luminosity// - What is the relevant opacity for these first generation stars? // Gave a bunch of wrong answers. Eventually, Eliot guided me to the idea that, in the early universe, there was no ionized oxygen and carbon to absorb UV photons. // ===== Petigura Cosmology ===== **Martin White** - Sketch the matter power spectrum. Label the axes. - How do we compute distance from redshift. //Hubble law.// - What about in the distant universe? //Wrote down the standard formula for proper distance as a function of redshift from the Friedmann equation.// - What happens to the vacuum energy term at redshift 5? - Why doesn't h matter at high redshift? //Flailed around for a while. Eventually, he said we know \(\Omega h^2)\ much better tan we know H. Moved on// - What is the difference between \(P(k))\ and \(\delta(k))\ - What would it look like if n doesn't equal 1. - How big would the perturbations be? - Is the power law approximation perfect. - Where do the slow roll parameters come from. - What do the peaks correspond to? ===== Stark Galaxies ===== - Why are potentials useful in galaxies? - What is the fundamental observation of galaxy that gets the mass profile? - How do you measure v_circ? - How do you know v_circ ~ const for a spiral galaxy? - What is the surface brightness distribution? - What does a bulge look like? - How do measure v_c(r)? - What does rigid rotation look like? (in spider diagram I drew) - What does a flat rotation curve look like? - How do you model a multi-component galaxy? - Why do you add v_c^2 and not v_c? - What does the exponential disk look like? - Can the rotation curve be explained by baryonic matter? - How do we measure the rotation curve of the Milky Way? - What is Oort A constant? - Where does it come from? - Where is it useful? - Draw v_r vs. galactic latitude profile. Explain. - What is relaxation time? - What is the value for stars near the Sun? ===== Stark Fluids ===== - What is the cross section for gravitational scattering? - What is the relaxation time in terms of the cross section? - What is the mean free path given the cross section? - Given the temperature of the corona T, density n, magnetic field strength B, rotation rate Omega... - Is the Alfven radius inside or outside the star? (I think I started too detailed and Eliot broke it down) - What is the Alfven speed? - Where is the sonic point? - How do you get the mass outflow rate? What determines it? - What is the value of Beta in the Sun's corona? - What is the energy source of the solar wind? - What are the assumptions that characterize convection in the Sun? - Are these assumptions true for convection in the atmosphere of Venus? How is it different? - How do we justify that solar convection is adiabatic? - What is the optical depth of the Sun? - We observe a star like the sun and see an oscillation with a period of a day. What is this? - What is the sound speed? What is the free fall time? - What is the dispersion relation for gravity waves? ===== Stark Cosmology ===== - What is the Lyman-alpha Forest? - What do you mean by "cloud" in LyaF? - What is the column density, physical density relative to critical? - What sets the properties of the cloud? - What is in halo relative to the background? - How far away is z ~ 2? - To what z is it ok to assume only matter and a cosmological constant? - Where does H(z) come from? What are Omega_m, rho_crit, Omega_m h^2? - Why do you constrain omega_m instead of Omega_m? - How well is omega_m = Omega_m h^2 known? - How do distances scales at low z? - Plot the power spectrum of DM fluctuations at z~2. How much does it evolve from z~2 to z = 0? - Once Lambda dominates, how does growth of delta_m change? - What is the nonlinear scale at z~2, z=0? - What sets P(k) ~ k at low k? ===== Fornasini Radiation ===== - What is the S-Z effect? - What kind of gas is involved? What particles are responsible for the Inverse Compton scattering? - What is the S-Z effect useful for? - Consider a CMB photon scattering off an intracluster gas particle: - What's the probability of an encounter? - What's the optical depth? - What's another name for optical depth, aka a visual/geometric interpretation of optical depth? (answer: covering fraction} - Estimate the optical depth for a typical cluster. - Is the Thompson cross-section the appropriate cross-section in this case? Is it always true for photons scattering off electrons? - In what reference frame is the Thompson cross-section appropriate? - What happens after the photon scatters? Is the scattering isotropic? - After scattering, what is the energy of the photon? Is it higher or lower? How do you boost between reference frames? - What is the sodium D resonance line? - What kind of transition produces it? - Why is it a doublet? What sort of process is responsible for splitting the lines? - What is fine structure? - What is the magnetic field that the electron perceives? - How would you estimate the cross-section of this line? Is it ok to neglect the stimulated emission? What are the relevant levels? ===== Fornasini Galaxies ===== - What is the Schechter luminosity function? - What is its meaning? - What is L_*? What is its relevance? - When integrating the Schechter function, what lower bound should we choose? - What is the mass function? - How and why does it differ from the luminosity function? - How can you measure it? - Do all galaxies obey the Schechter function? - What are cD galaxies? Why do we think there's an excess of them? - Ultrafaint galaxies: how big are they? How many stars do they typically contain? - What are the differences between dwarf ellipticals and dwarf spheroidals? - How do you know ultrafaint galaxies are dark matter dominated? - What is the mass of the Milky Way? How can we measure it? - How can we measure the mass of an external galaxy? - How can we measure the velocity curve in the optical? What is the brightest line and where is it produced? - How can we use this line (H-alpha) to determine the rotation curve of a galaxy? - Why is 21 cm better than H-alpha? - How does the radial extent of 21 cm emission compare to H-alpha? ===== Fornasini High Energy ===== - In what wave band can we detect 10^7 K gas? - What techniques are used to detect this gas? - What are most detectors made of? At what wave bands do we use NaI detectors? - Do modern X-ray facilities use gas proportional counters? What do they use? - What are cosmic rays (CR)? - Draw a spectrum of cosmic ray energies. - How can we detect 10^20 eV CR? How can we detect lower energy CR - Where are CR produced? How are they accelerated? - Is there a limit to the energy to which a CR can be accelerated? - What can produce CR with energies higher than those produced in supernovae? - What evidence do we have that the highest energy CR are extragalactic? - What is the distribution of CR on the sky? - What can you say about the formation of neutron stars? - What are the typical masses of neutron stars? What is the maximum mass of a neutron star? - Why do so many neutron stars have masses around 1.4 solar masses? - What have we learned from the Hulse-Taylor binary? - Derive the mass dependence on radius for the relativistic and non-relativistic case. - Tell me about the diversity of supernovae. - Why do we parametrize supernova energies in units of 10^51 ergs? ===== Price Galaxies ===== **Leo Blitz** - What is a galaxy? - What are ultra faint dwarfs? - Is 10^7 Msun luminous mass? - What's the difference between ~10^3 Msun dwarfs and globular clusters? - How is the difference manifested? - You mentioned the virial theorem. Write it down. - What does the kinetic term look like? The potential term? - Compare dwarf spheroidals versus globular clusters. Compare sigma and radius for the two. - What is the Tully Fisher relation? - Sketch the relation. How much scatter is there? - How is it measured? - Is it mainly from optical or radio or some other observations? - Why is this relation so useful? - What about TF at high z? - Let's assume it follows the same relation. - Is there a problem finding evolution? - What about 21 cm? (surface brightness gets too low at z >~ 0.1) - TF was found recently for ellipticals when CO was used as a tracer. - Is this surprising? Hint: what is being measured in terms of rotational properties? (Surprising to Leo since the gas was found in a disk. CP: well, gas likes to form disks.) - Where is CO in a galaxy typically found? What about in radius compared to 21 cm? - What would the rotation curve of a bulge be? Draw v_circ on your curve. - What about the disk? Do they contain DM? How do you know? - Back to TF. Where is the gas that contributes the widest part of your line located? - In an elliptical, what is the dominant mass component that you measure CO? - If TF from CO in ellipticals is the same as TF for disks, would you be surprised? - What kind of galaxy is the Milky Way? - Spiral. How do you know? - How do you measure the spiral arm structure? - Draw radial velocity versus galactic longitude. ===== Price Radiation ===== **Dan Kasen** - How do spectra of spiral and elliptical galaxies differ? - Why are spiral galaxies bluer? - How do you connect Halpha in galaxies to luminosity of a galaxy? - Compare Halpha luminosity to UV luminosity - Does every recombination produce an Halpha photon? - What happens to UV light that doesn't come out in Halpha? - Why does some of the energy go into the thermal pool? - Does anything go into the continuum? - Any continuum from recombination itself? - If density is too low, what happens to the equilibrium condition? - What sort of radiation processes might be important at other wavelengths (in galaxies)? - What about lines? - What is the process by which CO radiates? - Why does that give you a line rather than a continuum? - How do you amplify radiation into a maser-like emission? - What are the conditions to create a maser? - Can you ever get masing from LTE? What is LTE? - If we zoomed to a cluster of galaxies, what kind of radiative processes are important in the IC gas? - What does the spectrum of IC gas look like? - Why is there a cutoff in intensity? - How come all the IC gas doesn't blur or fuzz out the galaxies? - Why isn't the optical light obscured? - Is the gas optically thin? - What happens to photons that scatter? - How much energy does an electron pick up when it scatters? - What is the average energy produced in scattering? - Does a photon always pick up energy? - What other loss processes are there? ===== Price Cosmology ===== **Chung-Pei Ma** - What are the main components of the Universe? - What is radiation made up of? - What are the relative densities? - How do you know the photon value? - Does the CMB intensity depend on anything other than T? - How does the energy density of the CMB depend on T? - Can you prove this in a heuristic way? - How does T change with the scale factor for radiation? - What are the baryons in the Universe? - Do the observed baryons make up all of the non-dark matter? - Where is the rest? - Have there been experiments looking for MACHOs? - What is the warm component? - How do we know Omega_matter? - How do we estimate the neutrino energy density? - What is the criterion for a particle to be non-relativistic? - Is T_neutrinos the same as T_photons? What is T_neutrinos? - When did neutrino decoupling happen? - What are the major components of a galaxy cluster? - Why didn't you mention the dark energy in a cluster? - If the Universe had no dark energy, how would it qualitatively affect what we observe? - Would clusters still form in that universe? - How might cluster formation be different in that universe? - If the Universe had no dark matter, how would that affect structure formation? - How does dark matter help you get structure formation? - At what redshift do you start forming structure? - How do the different densities of the components evolve with time? - When did matter/radiation equality happen? ===== Weiss Radiation ===== **Dan Kasen** Blackbody radiation. - Why do stars have different colors? - How does peak wavelength depend on temperature? - Why are some stars very luminous yet cool? Spectral lines. - How can one see absorption lines? - What lines would you see when photosphere is hotter? - What function of temperature is the intensity? - Coolest stars don't have strong Balmer lines. Why not? - Why do these absorption lines disappear again in very massive stars? - What about atoms like He? Does it ionize at a higher or lower temperature than H? - What equations would you use to figure it out, assuming LTE? - Hold T fixed. Increase n_e. Will the gas get more or less ionized? Earth's atmosphere. - Why is the sky blue? Why isn't the sky violet then? - How would you calculate the specific intensity at some point in sky (away from the sun) due to Rayleigh scattering? What equation would you solve to find I_nu? Is tau a big or small # in this case? (Note of encouragement: I f*d this one up but still passed my prelim.) - At IR, what processes are relevant? - What physical processes are happening in these molecules? - Which mode gives lines in IR? - Why are atomic lines in optical/UV while these lines are in IR? Magnetic fields and high energy. - In a magnetic field outside a planet with ionized plasma, what kind of radiative processes are relevant? - What's the difference in non relativistic limit? - How much is it beamed? - If electrons are around 1 MeV, & you observe synchrotron at ~1 GHz. Estimate B. - What if you didn't know the distance, but only the frequency? - What is the emission spectrum if the electrons follow a power law E distribution? - What happens to the spectrum if injection of energy is stopped? - You said highest energy electrons cool first. Why? ===== Weiss Cosmology ===== **Chung-Pei Ma** - Could planets be dark matter? - Do you know what the primary candidate for Machos are? - How much dark matter do we think there is out there? - How much could be in Machos? - So you mention the baryonic dark matter, what are baryons? - What are example of baryons? - What do we know about their abundance? - What is h? - How do we know omega_baryon? (I got stuck on this one and floundered for a bit.) - When were the light elements formed in the history of the universe? - Let's connect the abundances to the baryon fraction, can you elaborate on how this is done? - Before the stars were made, what was the universe made of? What about the baryons? - You have electrons, protons, neutrons, etc. what is the first step of building other elements? - The ratio of photon to baryon is a key parameters. Is it easy to determine the photon abundance? How do I figure out how many there were 3 min after the big bang. - We want to find omega_baryon, so how can we do that now? - How does the helium mass fraction depend on omega baryon? - Sketch Y vs n_B/n_gamma - How does deuterium depend on this ratio - Do you know where the deuterium abundances are measured - Where is most hydrogen in the universe measure, and how? - Can you tell what the significance of the jeans length is? - What is the physical meaning of the sound speed? - What is the sounds speed of dark matter? - What is the implication of this? - What is the sound speed of baryons? What do you know about it? - How do you determine when the baryons were relativistic? Are they relativistic today? What is their rest-mass? - What was the sound speed during recombination? - After recombination, what happened to the sound speed of the baryons? - What is the implication for the Jeans length? - Do you know what the rough Jeans mass is right after recombination? - So since you mention galaxies, are they randomly distributed on the sky? - How can you measure the non-randomness? What is the general trend of a function of r? ===== Weiss Galaxies ===== **Mariska Kriek** - If I pick a random galaxy on the sky what is the probability of getting a given luminosity? - What is the curve called and what are different parameters? - Is this luminosity function the same for blue and red galaxies? - Say, in the local universe? - Where does the milky way fall on this plot? - What other galaxy properties may change along this curve? - And it what direction? - What about SFR, and specific SFR? - What about morphology? - What about the spectral type? - Is the spectral type more related to the SFR or specific SFR? - How does the sersic index change with luminosity? - What does the sersic index indicate? What does a high value mean? - Where would you find the boxy ellipticals in this curve? - What about disky ellipiticals? - What kind of hints do we have about the formation of boxy vs. disky ellipiticals? - What kind of processes are more important in dissapationless mergers? - What distributions of red vs. blue are different in a cluster environment versus a field environment? - Why are the magellanic clouds not red? - If we want to compare the blue vs. red population, is that fair to do at a given luminosity? - What about the stellar mass, would that be the same? - How do we go from a luminosity to a stellar mass distribution? - What are the key ingredients of stellar population synthesis? - Do you know another way using observations to determine the age, star formation history of a galaxy? - What is setting the timescale? - What is the largest uncertainty in going from luminosity to stellar mass? - IMF may depend on stellar mass. How do people actually constrain the IMF in external galaxies? - How could you distinguish red giants and red dwarfs in your galaxy model? - What are other ways of constraining the IMF, given you know everything about dark matter and black holes? - How do you get the mass of stars? - If you have a mass function of a galaxy determined using a constant M/L ratio, but if M/L is changing, how will that change the galaxy mass function? - How can we measure the M/L ratio along the curve? - What else can we do at the high mass end, besides measuring the dynamics of sattelites? - What do you have to measure of the galaxies if you want to determine the halo masses in which they live? - Are there other powerful ways to probe galaxies in clusters to determine the halos masses? - And if you go to low mass end, how would you study the halos? - What does the halo mass function look like? - What explains the deficit at lower masses? at the high mass end? - Why is it more powerful to use the evolution of the mass functions compared to the B-band luminosity function? - How can galaxies move in this diagram, what processes grow a galaxy? - What about major mergers? - Which direction does SFR go in the plot? - If you go to earlier times, how would the mass distribution of galaxies look in these diagrams? - Is the number density higher at earlier times, at a specific mass? - How do we measure merger rates over cosmic time? - What are large uncertainties, in looking at nearly merging galaxies? - How do we identify merged galaxies at high redshift? Do they look like regular galaxies? - What kinds of morphological properties can you measure of a galaxy? - To measure the Gini coefficient, do you want to look in a bluer or redder band? - How can you get a handle on the merger timescales? ===== Shivvers Galaxies ===== **Mariska Kreik** - What does a random galaxy on the sky look like? - What luminosity would a typical galaxy have? - What is the probability function for its luminosity? - What are the important parameters in this function? - Do red and blue galaxies have similar phi(L)? - Is color the only property that's changing as one goes to higher L? - How can you quantify morphology? - How does the Sersic index change at higher L? - What does the Sersic index measure? - What is the difference in light concentration between disk and spheroid? - Name another property that changes with L? - What other parameters make a galaxy redder? - Why are massive galaxies more metal rich? Talk about outflows. - Only look at the star forming population. Is the SFR decreasing with M*? Why? Plot it. - Only look at elliptical galaxies. Does SFR change with M*? - What are the differences between lower and higher mass Ellipticals? What do they tell us about the formation history? - Back to phi(L) for red and blue galaxies. Assume phi(L) is measured in a red band (say R). How would it shift in the B band? Do the curves move away or towards each other? - What about the mass function? How would it move? - How do we get from L to M*? What else do you need besides stellar spectra? How does metallicity go into the model? - Now look at phi(L) at different redshift. What kind of processes go into changing phi(L) at different z? - How does star formation affect the curves? How do mergers move the curves? - Compare L at different z. Is it fair to compare two galaxies this way? What is a better way to compare growths? - Now draw the mass function for stars and DM halos. Why is SF less efficient at lower masses? - What about the high mass end? ===== Shivvers Cosmology ===== **Chung-Pei Ma** - In cosmology, what do supernova data measure? - How do you know the intrinsic luminosity of supernovae? - What do you actually measure and plot in SN cosmology? - What is the definition of luminosity distance? - What are typical cosmological parameters to consider in standard models? - To zeroth order, what is the d_L -z relation? - How do you get the d_L - z from the Hubble law? - There are higher order z^2 term that comes in at higher z, what does this depend on? - What is the decelleration parameter, q? How does depend on the cosmological parameters? - What do the SN constraints look like in the omega_lam-omega_m plane? - What about the flat universe constraint? - What other data are providing constraints? - What do the CMB studies measure? - What does the angular power spectrum mean? - What does the horizon size mean? What is its rough size? - At what redshift did decoupling happen? - It is really the acoustic horizon, not light horizon, that matters, what does that mean? - What is the speed of sound in this early universe medium? - What are the constraints from the CMB power spectrum? - If the universe was more open or closed, how would the power spectrum change? ===== Shivvers Radiation ===== **Dan Kasen** - Let's consider emission from a type 1a supernova remnant, a hot bubble of 10^7 K gas, what do we see (i.e., thermal emission)? In what part of the spectrum would you see this? - If I want to know whether the cloud is optically thick or thin, what would you take into consideration? - Sketch a plot of cross section vs. energy, how would that look? - What is bound free absorption? - What is the Rydberg Formula? - Would you expect atomic scattering to be important compared to electron scattering? Why? - Say it is optically thin, and thermally emitting free-free, how could you calculate what the brightness profile looks like? - Let's say that this is thermal emission, what do you expect j and alpha to be? - If it is optically thin, do you know what the solution for I is? - If you go from the center to the edge, how does it look? Imagine there is an observer off to the side. How does the intensity look like as a function of the impact parameter? - How would intensity versus impact parameter look if the gas is optically thick? And with constant temperature? - If the supernova remnant was expanding relativistically, how would that change the plot of Intensity vs. impact parameter? - Ok, now forget about the relativistic part - how does the free-free emission spectrum look? - What is the limit for the highest energy photon you can produce? - You see emission lines from iron in the spectrum, at which wavelength do you expect to see these? - If we want to see if it is optically thick in these lines, how do we do that? - What are the requirements for synchroton radation? - Could you sketch out the spectrum from synchroton radiation? ===== Hand Cosmology ===== **Martin White** - Sketch the history of universe on the board. Distinguish between recombination and decoupling. What's first? - In addition to time, give scale factor and/or redshift as well. - When roughly is reionization? - How do we know we are going into a period of acceleration? - What is the definition of luminosity distance? - What is the chi factor definition of luminosity distance? How is the Hubble factor defined? Scale factor? - You've assumed, flat: what's the error on how flat the universe is from just CMB? What about when combining other data? - How would hot dark matter energy scale with redshift? - What is so important about inflation for understanding structure formation and what we observe? - What exactly is the horizon problem and how does inflation solve that? - How does structure grow? - What is typical size of potential fluctuation very early, e.g., time of Big Bang nucleosynthesis? - In particular, what is the potential fluctuation size outside the horizon? How does gauge choice affect this calculation? - How do density perturbations grow from recombination to present? What dominates the expansion of universe during that time? - How do we know all of the matter isn't baryons? If there were only baryons, would there be too much or too little structure? On what scales? - What is the ratio of dark matter to baryons? - How do baryons affect structure formation? Where do baryon acoustic oscillations come from? What sources sound waves? Evidence for fluctuations in baryon-photon fluid? - Plot the CMB power spectrum. What is scale of CMB power to order-of-magnitude? How is low ell CMB power related to amplitude of density fluctuations? If I view CMB as an acoustic cavity, what is Q-factor? - How does CMB power drop off at high ell? How is high ell power changed during propagation from recombination to us? What does lensing do at high ell? - Baryons have changed growth of structure by imparting oscillations in power spectrum. During formation of first stars/galaxies, how else are baryons important? Can you get collapsed structures in the absence of baryons? How do halos form given no dissipation? - When dark matter collapses, what is distribution of dark matter? How do we define halo mass? Are halos spherical? How triaxial? - Sketch slice through N-body sim of density field? - Does the shape of halo know about filaments? How long are filaments typically? What sets the scale of filaments? Are filaments linear or nonlinear? - Any other scale in the problem that is ~100 Mpc? What sets the scale of peak in power spectrum? ===== Hand Fluids ===== **Eliot Quataert** - When Kepler observers stellar oscillations, what are we actually measuring? - How does it observer stellar oscillations? What properties are changing? How does it change the flux? - What is the restoring force of sound waves? - What is the sound speed, how is that calculated or defined? - What is the physics behind the G-modes? What is the dispersion relation? - What is picking out r (radial direction) for the acoustic waves? What would r be in this room? What direction would it be? - So there is a funny result, if k_perp is zero, you cannot have gravity waves, but you can have a sound wave. Why can't you have a perfectly spherical symmetric internal gravity wave? - Eliot sketches frequency squared vs radial direction. Identify the G-mode and P-mode curves. - Imagine a mode that has a frequency that is a little bit less than the peak of the G-mode frequency curve. What is that mode? - Where is the region where that mode would decay? - We have neglected magnetic fields, give an approximation when that would be valid. - Given a magnetic field strength, how could you check quantitatively whether that is true or not? - Same question, but for rotation instead of magnetic field. - How is the Toomre Q defined? - Describe the physical when the Q parameter is relevant. - What are the assumptions? - What is the rough condition for instability vs stability? - Is this true in MHD? - How does this saturate? Does the saturation depend on anything? - Say you have a clump that is not rotating and is Jeans unstable. What is the timescale for instability? - If you derive the fluid equations from the Boltzmann equation, there is a well known complication. What is it? - How do you derive the fluid momentum equation from the Boltzmann equation? - What is the second moment that shows up? - And if the distribution function is exactly Maxwellian, what is the second moment? - And what about if it is just close to Maxwellian? ===== Hand Galaxies ===== **Mariska Kriek** - What galaxies are most common? - What does a galaxy luminosity function look like (plot it)? - What is the most common galaxy in a given volume? - Give an example of a typical galaxy. Would you expect it to be a spiral? - What kind of stars dominate at the bright and faint end? - What happens to the luminosity function if you go from g to r band? - If you want to trace a population across time, can you compare luminosity functions? - Why is it so difficult to go from light to mass? - Why is the IMF so problematic? - Give examples of different IMFs. - Is the IMF important for color evolution? What dominates color? - How does the stellar mass function compare to the dark matter halo mass function? - What does this difference mean? - Why are dwarf galaxies so inefficient at forming stars? High mass? - Looking only at ellipticals, are all ellipticals the same? - What are the differences between the two types? - How do you know stars in more massive objects formed over shorter timescales? - How does alpha/Fe tell you the time scale? - How can you explain the origin of boxy vs disky? - Can you explain the differences in isophotes? - Could you plot the color-mass relation? What causes the tilt in the red sequence? - How can you explain the mass-metallicity relation? Is it true in closed box models? - How do we know the Milky Way is not a closed box model? - What is the other tight relation ellipticals span? Is this relation unexpected? - Is the fundamental plane tilt related to the tilt in the red sequence? - For disk galaxies: what are the equivalent relations? - How are disk galaxy structures different from ellipticals? - What about dwarf ellipticals? How do they form? - What types of galaxies don't lie on the luminosity function you drew earlier? - What causes spiral structure in disk galaxies? - How are the stars moving? - How would a spiral galaxy look different at near IR wavelengths? Mid-IR? - How would you place a slit to measure circular velocity? ===== Burleigh Stars ===== **Eliot Quataert** -How do we define metallicity? -What is roughly solar metallicity? -Of the metals, what is the most abundant? -Why does stellar structure depend on Z? -At what temperatures is the metal opacity important? -Can you sketch the Rosseland mean opacity as a function of T? -What is the Rosseland mean? -If the metallicity were zero, how different would this curve be? -Would the H- opacity change if Z = 0? -Why are the metals important for the free electrons? -What aspect of the stellar structure does the opacity matter for? -Did you know there is a debate over the melallicity of the sun is? -Where does metallicity come into helioseismology? -What is the dispersion relation for a sound wave? -Can you sketch an HR diagram with the main sequence? -Can you tell me how effective temperature scales with mass for high mass stars? -How does the central temperature of a massive star vary with mass? ===== Burleigh Radiation ===== **Dan Kasen** -Suppose you have a cloud of gas, spherical, T=const, rho=const, kappa=const, is it optically thin or thick? -Explain source function for thermal radiation -What total luminosity for a optically thin cloud with thermal radiation? -How long would it take to cool? -Explain cooling curve: time vs temperature -Explain SZ effect -How would cooling curve look for free-free process at high T? -What are other processes at lower T? -Explain Ly alpha emission, j_nu(T), what is typical T where it peaks, what about at low T? -Explain rotations, vibrations, are they allowed for dipole moment? ===== Burleigh Cosmology ===== **Uros Seljak** -What does the power spectrum of CMB look like? -For scale the invariant power spectrum, how are potential fluctuations related to the power spectrum of temperature fluctuations at low "L". What are sources of CMB fluctuations on large scales? -Is ISW present on large scales? -How do perturbations grow in a matter dominated universe? What about potential perturbations? what about in Lambda dominated? -Write down the Friedmann equation? Do perturbations enter? -At late times, if have matter and lambda, what is in the Friedmann equation? -What are the peaks in power spectrum of CMB? How would you calculate sound horizon for CMB peaks? What is conformal time at LSS relative to today? Calculate it. -How can you get the angular scale of the first peak in CMB? How is angular diameter distance related to conformal time? -Can you get polarization of CMB? Why do you need thomson scattering? -What problems does inflation solve? What is the horizon problem? How does inflation solve this? What is the mechanism for producing fluctuations in potential etc. What is the equation for gravity waves. What is ground state according to QM?. What is ground state of Harmonic oscillator? -What are redshift space distortions? What is the kaiser effect? ===== ELee Stars ===== **Eliot Quataert** -Estimate L, R, Teff for a pure Carbon star on main sequence -Where is the core T from? -What’s different about this T? -How does this compared to electron rest mass? -What does fusion balance? Where are the neutrinos from? Where are the positrons from? -What is the average temperature of a (blackbody) photon for this energy? -What about R & L (for 1 solar mass)? -What have you assumed about this carbon star when you scaled quantities to the Sun? -What is the virial theorem for a white dwarf? -Plot R vs M for sub Jupiter mass to solar mass -Why the change of slope below Jupiter mass? -Function R(M) is not continuous. Where is this discontinuity? Why? -What’s special about 0.08 Msun? -Summarize uncertainties in modeling structure and evolution of stars. -Start with the Sun. -What quantities do uncertainties in convection affect? -How much mass is in convection zone? -What’s the biggest uncertainty in modeling the Sun’s evolution? -What’s the typical observed mass of a white dwarf? ===== ELee Fluids ===== **Chung-Pei Ma** - Imagine a ball of gas in hydrostatic equilibrium and the mass density is a powerlaw in radius. What are the equations that describe the gas ball? - Can you derive the pressure profile given the density profile (don't worry about the constants)? - If the gas is isothermal, what is the equation of state? - What radial profile does an isothermal ball has? And the profile of the pressure? What types of pressure is this? - What is the ram pressure? - Assume ball of gas has a circular orbit in a bigger potential. Relate ram vs thermal pressure - What happens to the pressure of the ball when it travels in a bigger potential - What happens if the assumption of hydrostatic equilibrium doesn't hold. - Does this equation hold for everything in the universe? Why is it called a fluid equation. - What is not a fluid? - Are photons in the cmb collisional - How would you describe things that are not fluids? - What is the connection between the fluids equations and the kinetic theory? - How else can you measure the velocity distribution in addition to mean velocity? - Can you write down the induction equation? - What is eta? - Let's go in the regime where diffusion is important. What is the typical time evolution? - What is the magnetic Reynolds number? - What is the typical Reynolds number of some spot in the ISM? What's the typical v? L? ===== ELee Galaxies ===== **Mariska Kriek** -how does SED and color of galaxy evolve as a function of time for a single stellar population? explain physically. -what about for a constant star formation rate? -for star forming galaxies, what is connection btw SFR and mass? -can you go from observed color evolution to SFH? -what would be a robust measure of SFH given dust uncertainties? -how do you use alpha enhancement to get constraint on SFH? -with short star formation timescale, would you expect higher or smaller alpha/Fe? -in what type of stars do you see Fe lines? -can you see low mass stars in star forming galaxies? -why is herschel such a powerful telescope for studying galaxies? -why is IR a good way to study galaxies? -what produces the observed FIR emission? -what types of galaxies produce FIR emission? -what does a dust attenuation curve look like vs. wavelength? -at FIR wavelengths, it’s about as easy to see a z ~1 and z~5 galaxy. explain why. draw SED of star forming galaxy? -how do you measure SFR from IR emission? -what are systematic uncertainties in estimating SFR from observations? -plot IMF. -what is the most common/abundant galaxy in the universe? plot luminosity function. -what types of galaxies are the low luminosity galaxies? morphology? -why are we sure that dwarf spheroidals are not ellipticals. -what is fundamental plane of Es? -is the existence of a FP surprising? -what is the origin of the tilt of the FP? -how might Z/Zsun change along FP? ===== Hirsch Galaxies ===== **Mariska Kriek** - What is the most common type of galaxy in the Universe? - What is the most typical galaxy? - Could you plot the probability distribution function of galaxies? - Is this really the probability distribution function if you look at the sky? - If I make a B-band luminosity function, what types of stars dominate? - Name some features of a galaxy spectrum? - What type of stars are dominating at the high luminsity end? - What stellar spectral type dominates? - How would your curve change if you go to a redder band? - What other properties are changing along this luminosity sequence? - What do you call this relation between rotation velocity and luminosity? - Does the velocity dispersion also go up? - What about environmental dependence? - What happens to stars that are stripped from galaxies? - How do we know if intracluster stars are or are not part of the brightest cluster galaxy? - Let's assume a galaxy has a group of stars all formed at the same time. How does the galaxy SED evolve over time? - Think about a galaxy with constant star formation rate? How does the color evolution look like? - Why does it still get redder? - Can we accurately infer star formation history from color? - So what is the best way to try to infer SF history? - What is one of the complications in using alpha enhancement to measure SF history? - Can you plot the mass-metallicity relation? - Why is the Hershel telescope so powerful for studying galaxies? - Where does the dust emission come from? - We see some very high-z galaxies with Hershel. Why are they reasonably bright? - Some of the inferred SFR are ~2000 Msun/year, this seems so high, what might be wrong with the inference? - What might you have to change in the IMF to affect the inference? - Why is it hard to make galaxies with 2000 MSun/year SFR in simulations. - How do we learn about the host populations of quasars? - How might we learn about the DM halos? - How can you match up quasars to galaxies using clustering studies? - From the angular correlation parameters, what do we learn? - If we go to higher z, does the correlation length go up or down? - What sets the clustering of galaxies, why do they cluster? - How would you go from an angular correlation function to a two point correlation function? - So how do you measure distance/redshift? - What feature provides most leverage for photometric redshifts going to come from LSST out to z=1? - What tricks might make photo-z's better, given only a few bands from LSST? - What priors can you use? ===== Hirsch Star Formation ===== **Steve Stahler** Large scale picture - What is the Hubble sequence of galaxies, and how does star formation vary along this sequence? - Within spirals how does SF varies? - What does a late type spiral look like? - Is there star formation in the center of the galaxy? - What is the color of the center of the galaxy? - What is a starburst galaxy? - Do people know what's causing a starburst? - What happens in a merger? - How do you know from a merger what the star formation is? - How do you go from these indicators to a SFR? - How do you know the timescale? Our galaxy - Do we see stars in the outskirts of the galaxy? - Do we see young open clusters in the outskirts? - Do we see old open clusters beyond us, thus further out? - Are selection effects playing a role? - Why is it hard to find an old open cluster in the center of the galaxy? - How do we see the galactic center? Moving down in scale - Stars are formed in GMC, and they are clumpy. How do we know that? - What is the main component? - Could you have H_2 without CO? - It is observed that the velocity dispersion varies with the size of the cloud - What is the column density through the cloud? - How does the column density vary from cloud to cloud? - What is the dependence of the magnetic field in the cloud as a function of M or L? - What did you leave out in the virial theorem? - What magnetic terms are you missing? - How does the magnetic field vary as a function of M or L? - How big is the magnetic field? Inside the cloud - give HR diagram for a very young cluster (3 Myr) - what is the lifetime of the sun pre-main-sequence? - What is the point where the lower envelop crosses the main sequence? - Now sketch a cluster for 3 *10^7 years - How old are the pleiades? - Which of these clusters is more likely to have class 0 sources - Which cluster is more likely to have weak line t-tauri stars - Which one could have post t-tauri stars? Jets - What is the difference between a jet and outflow? - How fast are the jets moving? - Does the wind speed go up or down while the star ages? - Why is the speed higher? - What is changing while the star ages? - How do we know that these jets are moving with 300 km/s? - What is the typical speed of a HH object? ===== Cheng Fluids ===== ** Chung-Pei Ma ** - What is the force on a charged particle in a electromagnetic field? - Can you rewrite this as a force density? What is rho, what is J? - How important is the first term for astrophysical fluids? - How big is rho usually for a gas cloud and why? - How does this enter into the fluid equation? - Write down fluid equation, what do the different terms mean? - If you were in a electromagnetic field, how would this equation be modified? - We would like to express this in terms of the magnetic field, what other information do you have to do this? - Which of the EM equation would help you to re-express the force equation in terms of magnetic field only? - What is the name of this equation? - How about the partial derivative term? - What does your force look like now? - Can you describe the physical meaning of the two magnetic forces? - What is the physical meaning of the B^2 term. What units is it in? - Is it an energy density? - What is the divergence of B? Why is it zero? - Consider waves propagating in the presence of a magnetic field. Could you describe the types of magnetic field waves? - Could you write out Alfven wave velocity? - Could you separate out the two modes? - Do you know how important the Alfven waves are compared to the sound waves? - Is magnetic field the only thin that matters? - Let's consider a rotating disk. Self-gravitating rotating disk of gas, mass M, radius R. What is the surface density? - We want to assess whether the disk is gravitationally stable or unstable. What forces are important? - Can you write down the acceleration for each term? - If you forget about pressure, what do you get? - What is the condition for gravitational (in)stability? - Do you know how it differs from the Toomre Q parameter? - What is the epicycle frequency? - How are kappa related to omega? - For solid body rotation how is kappa related to omega? - What is implication for omega for non-solid body rotation. Is omega a constant? - How is kappa related to omega? - What is the physical meaning of the sound speed? - What is the definition of sound speed? - We talked about the Milky Way, what is the Milky Way's disk made of? If we have a disk which is primarily made of stars, is this equation relevant? - Why are stars not a fluid? - Why are stars not collisional? - What is the force governing the interaction of stars? - Do people not use Toomre's equation to determine the stability of stellar disks? - Let's think about viscosity. What is the physical origin of molecular viscosity? - What does viscosity depend on? - Can you motivate why the second derivative of the velocity? - How important are these two terms? What does diffusion mean? Why is it relevant? - What do you think when you think about diffusion? What's behind random walk? Is it stochastic? - What happens to the last term? Is it important? Compressible fluid vs incompressible fluid. ===== Cheng Instrumentation ===== ** James Graham ** -What is a probability density function? Why are the moments interesting? -What useful quantities can you compute from this? -Is the 2nd moment always the variance? -Write down the relation between variance and the 1st & 2nd moments. -When is the variance the same as the 2nd moment? -What is the maximum S/N for an 8-bit (or 2^N) converter? -S/N=255/sqrt(12) -Where is sqrt(12) from? -Why is it a uniform distribution? -How do you increase the S/N? -Poisson processes: What is the rational behind the exponential distribution? -Give a back-of-the-envelope derivation of this distribution. -What is the Poisson probability for having 0 event (when the mean is 1?) -Write down PDF for a normal distribution. Why does Poisson have only 1 parameter? -How can this be dimensionally correct? -Parameter estimation: What is maximum likelihood? -What is Bayes Theorem? Be more concrete with A and B. -If data B are drawn from a normal distribution, express the log likelihood in terms of chi-square. -What is “x" you wrote down? -Express the likelihood for a set of measurements. -What is chi-square for a data set? Why is it a sum? -What is P(A) in Bayes? -Regularization in chi-square: What is the interpretation of a constant added to the chi-square? -What is P(B)? -If B is conditioned a second factor, expand out P(B). -HIRES on Keck: Slit width resolution is 60000/arcsec. -Start with the grating equation. Why is the resolving power dependent on the entrance aperture? -A finite slit has a finite range of delta alpha. How does this propagate into delta beta? -Draw a picture. How does the slit size affect the resolving power? ===== Wang Galaxies ===== ** Mariska Kriek ** 1. Sketch the luminosity function. - What are the important parameters? What is the slope? - What type of galaxies dominates the bright vs faint end? - Sketch it for the two types. - How does this function (in g band) change for ellipticals at z~1, passively evolving to z=0. - Would it shift more in b band cf g band? - Assume all blue galaxies are star forming galaxies at the same rate, passively evolving. - Does it depend on the band? - How does the total luminosity function evolve? - How do mergers change it? 2. JWST 0.6-28.5 um - What kind of radiation is it sensitive to? - What type of dusts? - Where is dust emission coming from? - Why is it an indication of SF? - Does dust obscure all types of stars? - How good a SFR does dust give? - Can one get dust temperature from JWST? - At what lambda does dust peak for a typical galaxy? - What are other ways to measure SFR (with JWST)? - Why is H alpha a SF indicator? - How is H alpha line made? - What types of regions produce H alpha lines? - Name a 3rd SF indicator 3. What properties of galaxies are useful for studying galaxy evolution? - Are galaxies brighter at higher z? - How do we measure dark matter halo masses for blue vs red galaxies? - What temperature is needed to produce X-ray hot gas? - Locally, do red and blue galaxies have similar baryon to dark matter ratio? - At higher redshifts, how do we learn about halo masses for blue vs red galaxies? - Plot two-point correlation function. What are the important parameters? - Is it really a power law? - Do red galaxies have larger or smaller correlation length? - Does correlation length increase or decrease towards lower z? 4. What properties define the Fundamental Plane? - What types of galaxies follow the FP? - What properties does the viral theorem relate? - How does the FP change with time? - The mass FP does not evolve with time. - What factors can tilt the FP? - What is a major uncertainty in stellar mass-to-light ratio? ===== Wang Fluids ===== ** Chung-Pei Ma ** - Hydrostatic equilibrium --- what does that mean? Write down the relevant eqn. - Where does this come from? How do you solve the equation? - Write down the Poisson equation. - What happens to the continuity equation? And explain the terms. - Now consider an isothermal atmosphere? How does it behave in equilibrium? - What is the profile? - Does this apply to the earth's atmosphere? - What is the adiabatic atmosphere look like? - What thermodynamic property is gamma related to? What is the constant and what does it depend on? - What is mu? - How does this adiabatic atmosphere behave (with altitude)? - Is density exponential for an adiabatic atmosphere? - Does the temperature change? How much? - What is the physical meaning of a sound speed? - Depends on ? - What is the definition? - What is the isothermal sounds speed for an ideal gas? - What is the adiabatic sound speed? - Which one better approximates the pressure waves in the room? - Let's apply hydrostatic equilibrium to a star. How are the circumstances different? - Can we consider some limits of the polytropic index? - What type of stars have n=0 and what are their properties? - Give examples of other polytropic indices. What about white dwarfs? - If I take a cup of water and inject some food coloring. What happens to the dye? - How does the color of the dye change the density of the fluid? Is the flow regular? - What are the properties of this instability? - What happens to the equation of hydrostatic equilibrium with the (dense) food dye and the water? Describe the profile of pressure and density. - What is a dispersion relation? What is it for free waves? - How can you tell about instabilities from the dispersion relation? What density conditions lead to instabilities? Does this happen for all wavelengths? What is the - role of surface tension? Can you describe when surface tension is present which regime is stable? - How is RT relevant for the Crab Nebula? - What can you say about the KH instability? - Do you know, in the absence of gravity, what happens? - What is viscosity? In what form does it enter the fluid equations? Why does it depend on the second derivative? Why is viscosity related to diffusion? What is the character of a diffusive process? ===== Wang Instrumentation ===== ** James Graham ** 1. Strehl Ratio / Statistics - Shopping expedition in an optics catalog. Diffraction limited optics, small print: wave front error lambda/4 pv. What does that mean in terms of wavefront error in nm. - What is lambda? - What is a strehl ratio? - What does a radio astronomer call a strehl ratio? - What quantity quantifies the wavefront error that the strehl ratio depends on? - Can you write down sigma_phi as a function of lambda/4 - lambda/4 is peak to valley, let’s convert it into rms error. Can you suggest a path to go from peak to valley to standard deviation? Assume uniform pdf. - What are angle brackets [in context of and ] - What is the standard deviation for a uniform distribution? - Now you have sigma_phi, what do you think the strehl radians is for these radians? - What happens to the strehl ratio if I have a sequential series of optics? 2. Optical Transfer Function - Can you tell me what the optical transfer function is of a optical system? - Can you sketch what a transfer function would look like for a perfect diffraction-limited optics system. Pupil function is square - Waht is nu_c? - What is the point spread function? [relate to imaging a point source] - So what is the relationship of the optical transfer function and PSF? - What is the PSF along a diagonal [of the square pupil]? - What is the asymptotic behavior of a sinc function? Relate this to the asymptotic behavior of the PSF of this square pupil along the sides and edges. - Some proposals to look at exoplanets, use pupils with pointy edges. Is there any relationship to what you just said? - So it would be nice to know what this critical frequency is in terms of some physical aspect of a telescope. - Can you express this in physical units? You are at a telescope for which you know the f-ratio. Say F/#=10 and 1 micron, what is the physical scale corresponding to that combination. - So the physical scale determines the pixel size. If I want to sample the signal with maximum frequency, what circumstances do I need to satisfy? - Can you sketch a proof of the sampling theory? [start with a band limited signal, then talk about Shah function] - How do I recover back the original band limited signal? [now that after sampling, your signal is infinitely replicated in Fourier space] - What Fourier theorem are you invoking? [if I want to interpolate the signal in between the sampled locations] ===== Goldstein High Energy ===== ** Josh Bloom ** - What are the types of detectors to detect high-energy photons. - Why don’t you just use a mirror? - Tell me about mirrors at grazing incidence. - What energies does NuStar go up to? Why is that interesting? - After a photon comes in a pair-produces, how do you measure angles? - What about the actual detections? What types of detectors are there? - What kind of solid-state device can you use? - Can you sketch the parts of a gas proportional counter? - What is special about Be for the window? - What effect makes Be not transparent to X-rays? - How does the slope of mu/rho go with energy? - What are the edges? What specific lines in the X-ray? - How does the curve change as I change the material I’m using? Normalization?? - Why is x-section much higher for lead? - Tell me about Gamma-Ray Bursts, as quantitatively as possible. - Is 1e51egs in gamma rays all of the energy released? What are the other channels? - Is the thermal energy more or less than 1e51ergs? - What other channels are there? Neutrinos more/less? GWs, more/less? - What progenitor systems could GWs be more than GR energy? - Are these most GRB progenitors? - In the dominant mechanism for GRBs do we produce a NS at the end? - Tell me about the distribution of GRB timescales… - What’s the emission mechanism for the photons [getting them out]? - At later times, what is the emission in the after-glow? - Why do we think GRBs are relativistic? Can you sketch out “compactness argument”? - What is the typical energy per photon? - How does relativistic expansion help? What are typical gammas you need? - Can you write an equation that relates accretion power with mass of a compact object and flow? - What’s the maximum accretion luminosity? How do you get the Eddington luminosity? - If source was radiating at 1e50ergs/s can I associate it with a mass? What kind of source is this? - What are some accretion powered sources in astrophysics? - If you saw a very bright quasar could you infer it was super-Eddington? - What are typical masses of SMBHs near us? What is the mass of SagA*? Is it radiating at Eddington? - Why might it not be radiating at Eddington? - Where is the energy released in an accreting system? - How might you not radiate the energy out? What is an inefficient flow called? - Let’s go back to super-Eddington…how do we make a super-Eddington outflow? - What’s the assumption about the geometry of the outflow? - Why does the maximum mass of a compact object depend only on physical constants? - Can you solve for the dependency on physical constants? - What principle sets the phase-space volume occupied by one electron? - Write the Heisenberg uncertainty principle. Solve for the energy. ===== Goldstein Radiation ===== ** Aaron Parsons ** - What is the equation for radiative transfer? What are the terms? - Can you construct me a source function? - Why do we care about a source function? - What does it take to turn I_nu into B_nu? What is B_nu? - What does local thermodynamic equilibrium mean? - Gas of a single atom: what kinds of temperatures are there? - What T is the one you wrote in B_nu? - What is the definition of brightness temperature? - How do you get that from the Planck function above? - Do I have to be in LTE for brightness temperature? - Let’s relax the LTE requirement… what are the 3 different temperatures? - Draw a big triangle with each corner being one of our temperatures. - What is the MB distribution function? Where do the pieces come from? - In gas cloud, want to equate T_K and T_B. Mechanisms that can do that? - Bathe gas in light with intensity given by T_B, how does T_K -> T_B? - What is inverse Bremsstrahlung? What is Compton scattering? - Which is more important? Why does temperature of electrons matter? - How would you tune light to get more energy into electrons using Compton scattering? - What is the cross-section for Compton scattering? - What if we look at maximum energy transfer (cos\phi=-1)? - Take two cases: lambda=1m, lambda=optical light. - What frequency would you pick for Bremsstrahlung? - Why is electron absorbing a photon at all? - What is the emission process that this is the inverse of? - What does the acceleration depend on? - How would you get more energy into gas through inverse Bremsstrahlung? - In what cases might that apply? - How does # interactions depend on speed? What about impact parameter? - Expression for collision rate, given cross-section sigma. - What about the other sides of the 3-temperature triangle? ===== Zick Radiation ===== ** Aaron Parsons ** - Can you write down the radiative transport equation? - Can you write down the units of specific intensity? - What are the units of \alpha? - Draw a picture of some cloud with a backlight and an observer. - Are \alpha and j independent? - Is it the case that you have to have local thermodynamic equilibrium? - What do you mean by "thermodynamic equilibrium" vs. "LTE"? - What matters: T_K, T_B or T_S? - Snu is a property of how material interacts with photons. - Could you rewrite radiative transport equation using Snu? - What if you integrate along \tau? - If \tau\to\infty then Snu -> Inu. - What mechanisms couple the different temperatures? - What if atom had a single electronic transition ... can you rewrite the transport equation in terms of that transition. - Einstein coefficients. - Can you write down the Planck function? - Why do they have the same factor out front? - Do we always have a Planck function describing our radiation? - Relationship between Snu, jnu and alpha_nu. - Once you achieve LTE, do you care what the medium is made out of? - It always ends up a black body? - Now I have more of a numerical question: - suppose you have a dense HII region with some He mixed into it (ionized once). - that He has a LyA equivalent transition. - how much does that transition contribute to the cooling of the (optically thin) cloud? - Give the high-level skeleton first. - Why might you care about C_{21} and C_{12}? - Cooling vs de-excitation?? - In a case where collisions are rare compared to A21? - What sets the timescale for emitting a cooling LyA photon? - IF you just had one He atom, and eventually a collision happens that bumps it to a higher energy state. - What sets the timescale of emitting a LyA photon? - The same collisions are causing the excitations in the first place: of A21 and C12 what sets the timescale for generating a LyA photon? - Suppose collisions happen very frequently...what dominates? - There are two pathways out of an excited state now ... - If collisions happen very frequently, what is n2/n1? - Lots of collisions make you go to a Boltzmann distribution. - Let's go back to the collision coefficient. Do we care about how much He there is, or what's hitting the He? - What is the distribution of velocities? - In the rate, does sigma_{12} depend on velocity? Why? - What other thing you need to know for the velocities is what T you're at. Any guesses? - What is the He fraction (from cosmology)? - Is it a mass fraction or a number fraction, or ... ? - Do you know A21 for H LyA? - How might that change for He? - How does nu^3 scale with Z? ===== Zick Cosmology ===== ** Martin White ** - When describing the Universe on large scales, we make some assumptions re symmetries, what are these? - How do we describe an isotropic and homogeneous universe - What does the metric look like? - What is a ? - What equation is governing the evolution of a ? - How is Hubble constant related to a? - What is omega_i? - What is the physical meaning of the critical density? - In more detail, is the universe still homogenous? - Is the CMB uniform? - How do I describe anisotropies in the CMB? - What about the spectrum as a function of frequency? - What kind of distribution has T? - And in spatial power spectrum? - Three regimes, what is setting these regimes (boundaries)? - For the scales in the left regimes, how was this generated? - What word do we usually use for power spectrum with n=1? - Why are the anisotropies damping out? - What sets that 2nd angular scale? - What process is happening when I take a snapshot of the cmb? - Is this rapid or does it take a long time? - If it was instantaneous, how would the right hand sight of the figure look? - What’s setting the oscillations? - It’s oscillating why? - What plays the roles of m and k (harmonic oscillator)? - If I run the university forward, what happens to the inhomogeneities? - What is T^2 - What is the asymptotic slope on the right hand side? - And the amplitude? - Are there features if you look more carefully? - What causing these wiggles? - Why are they smaller here than in the previous figure? - What makes up the matter? Ratio? - What suppresses the wiggles on the right? - You assumed perturbation were relative small? - What are dark matter halos? - Are they transient object? bound? - How do they look like? - What is the density profile? - What is the mass function of DMHs? - How does the mass function evolve over time? - How do I make a more massive halos over time? - What is the name of the process? - What is important about the dark matter in this context? ===== Zick Galaxies ===== ** Mariska Kriek ** - how is the color/mass relationship for galaxies related to the one for stars - how do minor red mergers affect the color of the main sequence - what happens to color if 2 red galaxies merged; where does it move on the sequence - what processes cause galaxy properties to change with time - how does the blue sequence evolve versus time - how does the specific star formation rate change versus redshift - what causes the specific star formation rate to go up with redshift for a galaxy of a specific mass - what are the assumptions that go into the spectral evolution of a galaxy based on stellar evolution - how would a shorter star formation timescale affect this evolution - which is a typical initial mass function for star formation; how does the IMF affect the galaxy spectrum - what would a top-heaving IMF do, keeping mass the same - how would dust in a massive galaxy affect the spectral energy distribution - where does the SED of dust peak, what dust temperature does this correspond to - what are the temperatures of star forming regions - are the UV & IR star formation rate indicators sensitive to the same stars - what does the attenuation curve look like for dust - how does one measure the dark matter halo mass of red/blue galaxies - for what galaxies does one use rotation curves to determine dm mass - what other probes of dm mass are there - what are different types of lensing - what about for the massive end of red galaxies (with very hot gas) - why does virial temp of gas only work on the most massive red galaxies - what process produces xrays in gas halos around massive red galaxies - how do people get dm halo masses at higher redshift - how is the clustering strength expressed; plot the correlation function versus radius for different redshifts - how do we measure clustering - is the correlation function describable by a simple power law - what analytic model does one use to describe the two terms of the correlation function - does the 1-halo or 2-halo term give us the mass of dm halos - sketch the halo distribution function - how does the halo distribution function change for more massive clusters - in this case, would you have more or fewer satellite galaxies - if the mass cutoff is increased, how does that affect the angular correlation function - how do Mstellar vs. Mhalo relate? ===== Zhang Cosmology ===== ** Martin White ** - How do we usually describe how galaxies are clustered? - Can you plot the power spectrum? Give axes and dimensions? How do we measure them? - Why do we use h Mpc-1 for k? - What do I actually measure if I measure a redshift? - What do I have to do if I work at higher redshift? What is the distance? - Where does the equation d_p = int dt/a comes from? - What distance is the r? - How is r related to dt? What is r? - What is d_p? - Does it makes sense to use h Mpc^-1 at high redshifts? Let's say 3? - What is the value of a? - What is omega_lambda and omega_matter today? - At redshift 3 what is the relative size of terms in the d_p equations? - How far do I have to go back to when the last term becomes relevant? - How is omega defined? - What is the critical density? - Do we know omega_matter well? - So at redshift 3 I don't want to measure it at hMpc^-1 right? - So if compare high redshift in Mpc to low redshift hMpc^-1, can I determine h? - Let's look at the power spectrum again. Could you tell me roughly speaking what the slope and scales are? - What sets the position of the peak? - And the little bumps you draw in the power spectrum? - Why is that bump moving in the first place? What force is driving it? Why does it stops? - Why did the decoupling happen? - Was that a gradual kind of thing or pretty quick? - Roughly when and at what redshift? - Rough duration? - What's the temperate of the universe at redshift 1100? - What is the energy (kT)? - Why isn't it 13.6 eV? - Why am I out of equilibrium? - What is the relevant interaction rate? - Is the recombination rate faster or slower than the expansion rate? - So I am in equilibrium, why am I not recombining at 13.6 eV - How many more photons are there? - Explain the slope of the power spectrum on the left side. - What is it that is scale invariant? - What is the dimension of P(k) - How is the gravitational potential related to the density? - Why does it make sense that the potential is invariant? ===== Zhang Radiation ===== ** Aaron Parsons ** - Write the radiative transfer equation. - What is the source function? - Can you integrate over s for me? - In an optically thick medium, what dominates the specific intensity? - If you were in thermal equilibrium, can you tell me something about the source function? - What is the -1 about? - Write \alpha's and J's in terms of Einstein coefficients? - Can \alpha_\nu depend on direction? - What are the unit of B? What about \bar{J}? - Do I need all of the alpha's and n's? - Can you tell me a little bit more about phi? - What dominates the width? Suppose you had some random motion? Does Doppler broadening dominate the whole width? In what cases might Doppler dominate? Where around the line are the two different profiles dominant? - Suppose you had a single atom at rest, what would phi look like? - Suppose I had two atoms moving relative to one another? What about a third? - What is the name for a convolution of a Lorentzian and a Gaussian? - Suppose I have an HII region that has been ionized with some He mixed in, as it gets ionized we ionize the He as well. What contribution is the He making in cooling the HII region from 10^4K? The power radiated. - What processes could be cooling? - What is thermal bremsstrahlung? What charges are interacting? What ions are at your disposal? - What do you expect the emissivity of p+e to look like? What about for the He? - Is that the only way e-He interaction can radiate? - Can you write out the bound-bound transition? - Is A21 the rate-limiting step in cooling here? I have some He and it's radiating off He, it drops from an excited to de-excited state is it never going to radiate again? How can it be re-excited? Is the B12 term important for cooling? Suppose we're optically thin, would it be important? - Let's talk about collisions. Can you write down something comparable to A21 for collisions, a rate? What is n counting? Which n is most important? Let's limit ourselves to e's. What would you use for sigma? Is Coulomb focusing important for cool or hot regions? What is the a0 that you've written? How is a0 for Hydrogen different than for He? What would you use for v? Are all electrons moving at the same speed? ===== Zhang Galaxies ===== ** Mariska Kriek ** - what are 2 most important observable properties of galaxies - draw color vs mass plot for galaxies - what is the name of the "sequences" of colors vs mass - why 2 different sequences - what type of stars dominate red & blue sequences - where are fast/slow-rotating ellipticals on red sequence - difference between fast & slow rotators - what sets to slope of the red sequence, and how related to rotation - what makes galaxies redder - why two different groups of ellipticals - what is the difference between dissipative & non-dissipative mergers - what processes cause galaxy properties to change with time - what happens to color if 2 red galaxies merged - why can hot gas cool in mergers, but not in pre-merger galaxies - what else (besides mergers) causes color evolution in galaxies - what does adding blue galaxies that quench do to the color distribution of galaxies - what causes the color vs mass slope in the blue sequence - what property does color reflect for galaxies on the blue sequence - what determines how many massive stars are present in galaxies - how does star formation rate scale versus mass - do massive star-forming galaxies have more/less gas than less massive ones - how does the evolution of the specific star formation rate versus mass influence the blue sequence - how does the blue sequence evolve versus time - how does the specific star formation rate change versus redshift - what causes the specific star formation rate to go up with redshift for a galaxy of a specific mass - why was there more star formation at higher redshift - why was there more gas available at higher redshift - where does the gas come from for star-forming galaxies at high redshift - how does one measure the dark matter halo mass of red/blue galaxies - for what galaxies does one use rotation curves to determ dm mass - what other probes of dm mass are there - what are different types of lensing - what about for the massive end of red galaxies (with very hot gas) - why does virial temp of gas only work on the most massive red galaxies - what process produces xrays in gas halos around massive red galaxies - how do people get dm halo masses at higher redshift - how is the clustering strength expressed; plot the correlation function versus radius for different redshifts - is the correlation function describable by a simple power law - what analytic model does one use to describe the two terms of the correlation function - does the 1-halo or 2-halo term give us the mass of dm halos - sketch the halo distribution function - how does the halo distribution function change for more massive clusters - in this case, would you have more or fewer satellite galaxies ===== Krolewski Radiation ===== ** Aaron Parsons ** - What is the radiative transport equation? - what are all of the variables? - what is specific intensity, what are the units? - Divide the equation by alpha_nu. - What would you use for S_nu in thermal equilibrium? - What is a black-body? - What is tau, and what does it mean? - If you have absorption and source, what is scattering? - What is required to observe the source function? - Write down the Einstein relations for a 2-state atom. - what is A and what is B? what are the g's? - when does this relationship hold? - What is j_nu in terms of A, B, etc. - What can set the width Delta nu? - What is the line profile function? - What is alpha_nu in terms of A, B, etc.? - Can you make the extinction term negative? - Could you construct an estimator for an atomic cross section? - What does LTE mean? - Write down a function for each temperature term. - At what z was the p, e and photons of the CMB in equilibrium? - If there were no electrons, would the coupling to protons be enough to keep them at the same temperature? - assume t~300,000yr to get H - have sigma ~ 10^{-6} sigma_T - compare np.sigma.c with H. - not sufficient to keep them in equilibrium. - But what physically is this interaction between photons and electrons? - How much energy is exchanged in one of these interactions? - Do you know a formula which could give us energy exchanged? - How big is h/m_e.c? - A typical wavelength at z~1000 is 10^{-4}cm. - What is the fractional change in energy in a collision? - Energy exchange is very small, so why are photons and electrons at the same temperature at high z? ===== Krolewski Galaxies ===== ** Mariska Kriek ** - why do we think low-mass galaxies reionize the universe - what galaxy properties yield ionization - what galaxy properties affect UV continuum emission - what affects the initial mass function of stars in a galaxy - how is the James Webb Space Telescope going to help us understand reionization - how do stellar population synthesis models work - how do stellar abundance patterns tell us about star formation history - how can a galaxy spectrum differentiate short or long star formation periods - why are high redshift observations better for measuring stellar abundance - what are high velocity clouds and how do we find them - how do we know these clouds are infalling and not produced by the fountain model - picking a random star in the universe, what galaxy is it most likely to be found in - describe the luminosity function of galaxies - what are the mass, color, age, and metallicity of a typical random star - what sets the metallicity of a star - how do we know that galaxies accrete new gas - why does a leaky box model of galaxies have a different distribution of stellar metallicities than a closed box model - what other evidence is there that galaxies are not closed systems - what is the Atacama Large Millimeter Array - what types of galaxies can ALMA find - can ALMA constrain the temperature of the dust if we don't know the redshift - what type of light heats the dust and what stars source this light - other than dusty galaxies, what can ALMA observations tell us - why are we missing CO emission in high redshift galaxies - how do know so much about host galaxies and host halos of AGN, given problematic observing - what do clustering measurements tell us - describe the angular correlation function of galaxies - how to the bumps in the angular correlation function change with redshift ===== Krolewski Cosmology ===== ** Martin White ** - What is the CMB? - What is the T of the BB? - What is the peak frequency? - The BB was measured back in early 1990. Not much advance, but still CMB knowledge has improved, so what has everyone been doing. Could you make a plot of the power spectrum? - What is l and c_l? - Why l^2 times c_l? - What are the dimensions of c_l? - What would be the power of log l? - What if the sky would be conveniently flattened, and I give you a power spectrum, what is the total fluctuation power? - How is the variance of the field related to the power spectrum? - What are the angular scales of the three different regions in the power spectrum. At what ls are they? - What physically sets those scales? - I am looking for a word with the letter H - What about recombination determines how far those photons can travel? - How fast does the process of recombination happen? In delta z? - What sets the number of times they scatter? - Let’s imagine that I could suspend the laws of atomic physics, and do this process instantaneous, would there be more or less small scale power of the CMB? - What happens to the mfp once we are recombining? - What else can I measure from the CMB? What kind of polarization? - Which of those stokes parameters are populated by the CMB? - How much is it polarized? - What sets this magic 10% number? - So you mentioned BAO, what’s the other power spectrum people usually plot in cosmology - Why do the DM fluctuations not grow? - Suppose I am jeans unstable, how does the amplitude grow? - What sets the strength of the damping? How is this related to the Hubble cst. - With a microscope, is this curve featureless? Could you show the fine details? - How are these wiggles related to the previous wiggles you have drawn - What is omega_b over omega_m - What is dark matter? - What do I know about dark matter? - What are the T limits? - Non-cold dark matter could be neutrinos. And we only have upper limits on their effect on the power spectrum. What is the critical density of neutrinos? ===== Gorthi Stellar Populations ===== ** Dan Weisz ** - Draw an isochrone for a typically old globular cluster (V-I vs I). - Label main phases. - What happens in each branch? - When does He burning start? - Write down a likelihood function for a single star. - What non-cluster things could this depend on? - How does a change in the distance affect the model in CMD space? - What about age? - What about dust? - What about metallicity? - Let's talk about marginalization. - What is the marginalized distribution for distance? - What is Gaia going to do for MW globular clusters? - What is the advantage of that? - What happens if dust is not homogeneous across the sky? - If CMD is broadened, what would you think it was due to? - What obs evidence suggests globular clusters are not SSPs? - What changed with the advent of UV? Why? - Discuss FRMS/MIB vs AGB scenarios. - Can you draw the CMD of a typical ultra-faint dwarf around the MW? - How do SFHs change with luminosity? - What processes in the early Universe could affect the SFH? - What processes could quench the more luminous dwarfs? - How do you convert UV luminosity into a SFR? - What uncertainties are there in this process? - Plot SFR(Halpha/UV) vs. luminosity. - Why the trend? - Where is the Halpha line? - What causes the Halpha emission? - Could a change in the SFH explain this trend? - Draw a schematic SFR vs. time. - To make the trend work, what does the SFH have to do? ===== Gorthi Fluids ===== ** Chung-Pei Ma ** - Are photons a fluid? - Consider a self-gravitating, rotating disk — what are the relevant forces for disk stability? - For a non-rotating disk — what is the condition for gravitational stability? - What is the Toomre parameter (Q), and what is its physical meaning? - What is the Milky Way (MW) disk made of? - Is there more dark matter or baryonic matter in the MW disk? - What is Q for the MW disk? - What is the rotation curve of the MW? - Give a few examples of turbulence in daily life. - Why is turbulence so common? - What is the Reynolds number? - What is it typically for daily life? - What is the Kolmogorov spectrum? - What is the magnetic induction equation? - In the diffusive regime, what is the time dependence of the magnetic field? - What regime is a perfect conductor in? - What are Alfven waves? - What are other MHD waves? - What is the Navier-Stokes equation? ===== Suess Instrumentation ===== ** James Graham ** Probability - What are some different definitions of probability? - What is Laplace's definition of probability? - What are Cox's rules that axiomatize probability? - What is a conditional probability? What is Bayes' theorem? - What are priors in Bayes' theory? Probability distribution functions - Can you derive the exponential probability distribution using assumptions about the time interval between events? - Given a PDF, how do you get the mean? The variance? - What is the mode for the exponential distribution? - What is the characteristic function? When is it useful to use? - What if we have quantities distributed with equal probability in, say, t^2 instead of t. How do you get the PDF for the former given the PDF of the latter? Error analysis. Given y(u, v, w, ...): - What is the variance in y given the variance in u, v, ...? - What are the covariance terms? - Can you derive the expression for the error and show where covariance comes from? Photoelectric effect - Sketch a circuit showing how you would measure photocurrent. - What type of solid is used to measure photocurrent? Why? - Consider an insulator like diamond-- why not use it as a photoconductor? - What is the band gap for diamond? What about for Si or Ge? - Back to circuit... what is the equation relating photocurrent and incoming photon flux? What about in the case of a solid state photoconductor? - What is the gain? - Explain doped semiconductors. What is the origin of the potential difference between p type and n type? - What is the depletion region? - What is the responsivity of a photodiode? What is it in real units? - James pulls out a real photodiode and DMM and asks me to measure the power of his laser pointer ===== Suess Fluids ===== ** Chung-Pei Ma ** Consider the forces acting on a rotating disk of gas - Do a dimensional analysis of the force balance. - What is the physical interpretation of this? - Turn off rotation. What happens? - How does rotation modify this picture? - What if all three forces are operating? - Use your expressions for the forces to identify stability vs instability. - How is this relevant to the Milky Way? What about Toomre Q? - What are the differences between stars and gas? Are stars collisional? - Make some comments on the epicyclic frequency kappa - What is Sigma for the Milky Way? - What is the rotation speed at the solar system? - What is the velocity dispersion? - What's the value of Q? - Talk about sound speed. What's the definition? - What does the sound speed represent? Relate to the equation of state. Shocks - What is the Sedov-Taylor solution? - What does it describe? What is the physical meaning? - What are the assumptions? - What is the characteristic timescale or time scaling? - Where has this been observed astrophysically? MHD - What is the force on a charged particle? - How do you add this to the Euler equation? - What are the magnetic terms? - What is the magnetic induction equation? - What is the coefficient before the grad^2 B term (eta)? What is the meaning of this term? - Which regime dominates in astrophysics? - If diffusion is important, what is the time dependence of B? - What are Alfven waves? What are pure MHD waves? - What are the properties of Alfven waves? - Are these the only waves that can be supported? - Would these waves perturb the density? ===== Kern Cosmology ===== ** Uros Seljak ** - How are SN used to measure the expansion of the universe? - What are sources of noise in this measurement? - How do we calculate peculiar velocities in linear theory? - What does the matter power spectrum look like as a function of scale? - At what scales does the growth of perturbations go non-linear? - How do we related the power spectrum of velocities to the matter power spectrum? - Show how we linearize the fluid equations in linear perturbation theory. - What is the amplitude of the power spectrum of peculiar velocities at the scale at which perturbations go non-linear? - What are sources of scatter in measurements of the expansion of the universe with SN that are not intrinsic to the SN? - How does gravitational lensing affect the image of a distance galaxy in the weak lensing regime? - How do you relate the shear of an imaged galaxy to the deflection angle in gravitational lensing? - What is the typical magnification from weak lensing fluctuations? ===== Kern Radiation ===== ** Aaron Parsons ** - write the radiative transfer equation, explain terms, explain specific intensity, explain optical depth - rewrite in terms of optical depth - what is source function - solve RTE for homogenous medium - what is source function in LTE - what is planck function - what are emissivity and absorptivity for 2-level atom - what are As and Bs - what are einstein relations, derive them, do they depend on LTE - how do you get LTE, what does it mean - what are the different temperatures that come into equilib in LTE - what are the physical processes that couple them - Question: - imagine a pure H gas cloud at 100 K, what density is needed for levels of 21 cm line to be set collisionally? - what collisions are key and what is the collision rate? - explain physically the critical density? - is the critical density you derived likely to be astrophysically realized? - what is the average density of the MWs ISM? - what is the A coefficient for 21 cm? - what if you didn’t remember it? how might you derive it? - what is the electric dipole moment of the H atom? magnetic dipole moment? - what is synchrotron emission? - given e of some gamma, what freq does most of the sync. radiation some out at? - where does gamma^2 in synch. formula come from? - In electron reference frame what is the emission? ===== Kern Stars ===== ** Eliot Quataert ** The note taker never submitted their notes to Dexter and lost them, so this is just my vague recollection of themes (from a year ago..) - White Dwarves, degeneracy pressure derivation - HEQ, core Rho-Temp evolution, He flash - Chandrasekhar limit, (in)stability analysis - Type 1A SN - SN Ejecta propagation, radiation