Studio Exercise Week 6
Calculating the Zero Age Main Sequence (ZAMS)
The code (ZAMS) used in this exercise is copyrighted.
It is taken from "Stellar Interiors" by Hansen and Kawaler, published by
Springer-Verlag.
I have obtained express permission from one of the authors (Kawaler) and
from the publisher, so that it may be used in 79205 Astronomy.
Do not copy this code if you are not from my class,
unless you have received permission to do so from the publisher.
Hansen and Kawaler describe the how to use the code in a
readme file.
The procedure is quite simple.
Run the program, and answer the questions. You are asked to specify the
mass of the star and its chemical composition, i.e. hydrogen and helium
fractions X and Y. You are also asked for good starting values for the
iterating algorithm. Output goes to a file name which you specify.
Sample inputs for
one and
fifteen
solar mass stars are provided.
(For this exercise, you do not need "pulsation" output.)
The output file contains lots of stuff, including the pressure and temperature
and other quantities as a function of the radius of the star.
The output for one solar mass is also provided.
All you really want is the first part of the output, i.e. just after
"*****FINAL MODEL*****" the program prints out the central pressure and
temperature, radius, luminosity, and effective (i.e. surface) temperature.
An executable image is provided for you on the studio PC's.
Alternatively, you can compile and run the program on UNIX.
Here is the fortran code
which you can compile using the "xlf" command in AIX, for example.
You do not need any special libraries or other fancy stuff.
The Exercise
Run the program, and keep a table of the output, for various reasonable
values of the mass.
You should tabulate the luminosity, effective temperature, and radius,
as well as the mass.
Use the same values for hydrogen and helium fractions, say typical Population I
numbers X=0.74 and Y=0.24.
Make a plot of the main sequence HR diagram,
using the "physical" quantities of log(Luminosity) versus log(Temperature).
Label the points with the value of the mass.
Does this look correct?
How do the values compare with the calculation listed in
Karttunen?
Make plots of the luminosity and radius as a function of mass
Does the luminosity go like the mass cubed?
Does the radius increase a bit more slowly than the mass?
Investigate the dependence on chemical composition.
Pick one value of the mass, and vary X and Y.
How does a pure hydrogen star differ from a normal population I star?
Suppose there is no metal fraction, i.e. Z=0 so that X+Y=1.
Make a plot of one or more calculated parameters, such as the radius,
temperature, or luminosity, as a function of X.
