Astronomy 210 Class Work (Jan 29)
1. Elliptical Dynamics
Look at this V/sigma vs ellipticity plot. (Note that
ellipticity = 1 - b/a, where b=minor axis, a=major axis of an ellipse.)
Consider the following questions:
(a) Where do most ellipticals fall in the plot? What does this
tell you about their rotation compared to their random motions?
(b) The line labelled Oblate marks the line
along which rotationally-supported objects would lie. What types of
objects tend to lie along this line?
(c) Now look at this plot , with symbols representing luminosity. Read the
caption for the explanation of the symbols. Does the likelihood to
be rotationally supported depend on luminosity? If so, how?
(d) Ellipticals often have isophotes that are not perfect
ellipses. Two of the most common deviations are 'boxy' and 'disky'.
Take a look at these elliptical galaxy light models . Identify the objects
with boxy isophotes and disky isophotes. See also Figure 3.7 in your textbook.
(e) Now look at
this
V/sigma vs isophote shape plot. The parameter 100 a4/a is
positive for disky isophotes, negative for boxy isophotes. How does
the isophote shape correlate with the V/sigma, i.e. the degree of random motion
observed?
(f) Look at your results from above. Summarize what types of galaxies
are dominated by random motions. What types are dominated by rotational
motion? Do any of the properties you found above seem to go together?
(g) Based on these results, Kormendy and Bender (1996) suggest
A
Revision of the Hubble Sequence for Elliptical Galaxies. Describe
the reasons for their suggestion.
2.Stellar Evolution
Go to Stellar Evolution Applet (Terry Herter, Cornell) .
Read the description, then follow the instructions.
Then think about the following questions:
(a) Summarize how stellar lifetimes on the main sequence
depend on their mass.
(b) Summarize how stellar lifetimes as red giants
depend on their mass.
(c) How do you know that star formation has occured recently
in a galaxy with a blue color?
(d) Consider the stellar population of an elliptical galaxy. In
what phases of stellar evolution do you expect most of the stars to be
in? What kinds of stars (i.e., in what phase of evolution) do you
expect to dominate the light of an elliptical galaxy?
Last updated January 29, 2008