Ay 124: 			Homework #3 ("it's good for you")
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0.  Read as many reviews as you can squeeze in your busy schedule 
(but >0, I hope) on the topics of star counts, Galactic structure,
mass models, the ELBS picture and its aftermath, Oort's limit, etc.

1.  Write TWO reports in the usual format (size ~ 1 - 2 typed pages
    or equivalent) on two papers of your choice from that list of
    topics, but the two topics ought to be different (e.g., one
    on the mass models and one on the ELBS picture; an so on).

	This is due on Thursday, Feb. 1.

Then do one of the following two (both if you wish):

EITHER:

2a. Write one more reading report on yet another paper on one of the 
    topics listed above.

	This is also due on Thursday, Feb. 1.
OR:

2b. A computational problem.  For this, a team (n < 5) work is encouraged, 
    but individual efforts are OK, of course.  If you opt for this (2b), 
    you will have one less report to write the next week!

	This is due on Monday, Feb. 5.

    Assume a mass model for the Galaxy, either the Bahcall, Schmidt, 
    and Soneira, or the Ostriker and Caldwell.  Truncate everything 
    at 50 kpc.  Assume that the spheroid, central, and dark halo 
    components have a constant line-of-sight velocity dispersion of 
    100 km/s (what's that in 3-dim.?), and the following rotation 
    curve: a linear rise from 0 to 220 km/s in the radial range 0 to 
    1 kpc, and the flat 220 km/s afterwards.  Assume that all of the 
    disk kinetic energy is in the rotation.  At any given radius, 
    ignore the potential energy of the disk beyond that radius.

    Compute the following quantities as a function of radius, for all 
    the components separately, and for the sum total:  the enclosed 
    mass, kinetic, potential, and the total energy, and the angular 
    momentum (for the disk only).  After you have the mass profile, 
    you can evaluate the velocities; do so and compare with the above 
    assumptions.  Present your results in a graphical form.

    A hint: have all the scaling parameters in your code easy to 
    modify.  Try to vary them, and see how the results change (e.g., 
    the halo mass).  Another hint: use sensible units.

    If you need a computer account, I will gladly open one for you 
    in CTARGO.  Do not hesitate to come and ask questions if you get 
    stuck somewhere.  Don't waste your time on technical problems.