Zero Age Main Sequence Models
We will use Carl J.Hansen and Steven D.Kawaler's zams code to calculate Zero Age
Main Sequence models. This code is very easy to use, and it doesn't take too
much time to compile it.
To download the code click here
then untar it by:
% tar xvf zams.tar
The tar file should contain the 6 files as described below:
ZAMS.FOR = Fortran source file for ZAMS model builder
ZAMS.EXE = PC executable code for ZAMS model builder
MODIN.001 = Sample input for 1 solar mass model
MODIN.015 = Sample input for 15 solar mass model
MODOUT.001 = Output for 1 solar mass model
MODOUT.015 = Output for 15 solar mass model
The files fall into two categories: programs and input-output files. The program
ZAMS.FOR computes zero-age main sequence models (one model per run) and you can
analyze these models for pulsation using PULS (We won't use PULS code).
The source code ASCII file is written in standard FORTRAN. We also include the
corresponding executable file ZAMS.EXE for use on PC's. These have been
compiled using Microsoft FORTRAN ver. 5.0 and should be ready to run on you PC.
Running time for ZAMS.EXE for the 1 solar mass model using the input discussed
below is ~30 seconds on astro.
The ASCII files MODIN.001 and MODIN.015 show what your screen might
look like after you have entered input for calculating 1 or 15 Msun
ZAMS models using ZAMS.FOR or ZAMS.EXE with X (hydrogen mass fraction)
equal to 0.74 and Y (helium mass fraction) equal to 0.24. We advise
you to try out this input with their corresponding guesses of central
pressure and temperature, and surface radius and luminosity (in units
of Lsun). If you have chosen MODOUT.001 or MODOUT.015 as the file
names for output, then our files MODOUT.001 or MODOUT.015 on this
tar file should be identical to your output files. You should print out
these files to identify the output variables. So, for example, the
first block of output recalls your input (mass, composition, central
pressure, [Pc], etc.) and is followed by information relevant to
iterations and convergence. You will usually not need this information.
After the line "FINAL MODEL" we have the output for a fully converged model.
The first bank of lines consists of indexed columns. The first column gives the
relative mass interior to the surface (1-Mr/M) where Mr is M_r (the _
means subscript) and M stands for mass and r for radius. The other
columns list the base 10 logs of radius, pressure (P), temperature (T),
density (RHO), and interior total luminosity as a function of radius
(i.e., L_r). The second bank of columns list the logs of energy
generation rate (EPS), opacity (OP), convective luminosity (Lc) as a
function of radius, the ratio of convective to total luminosity
(Lc/Ltot), the actual Del (DEL), and then Delad (adiabatic) and the
radiative Del (DELRAD). With all this information you should be able to
figure out what's going on in the model ZAMS star.
The pulsation code PULS.FOR (or PULS.EXE) uses output from ZAMS. You
ask ZAMS for this output by answering y (or Y) for "yes" when ZAMS asks
"DO YOU WANT PULSATION OUTPUT (Y/N)". Please answer this with n or N,
so that you do not get that output.
Compilation is done as follows:
% f77 zams.for
and it will create an executable file called a.out. You can use this executable
file on astro or zams.exe on your PC to calculate ZAMS models.
any questions: please e-mail email@example.com
Let's create a ZAMS model for a 1 solar mass model with composition
X=0.74, Y=0.24, Z=0.02 (solar metallicity).
[on astro] type
Then the program will ask:
THE TOTAL MASS IS (IN MSUN)
X(Hydrogen) AND Y(HELIUM) ARE
GUESS FOR CENTRAL PRESSURE (IN CGS)
GUESS FOR CENTRAL TEMPERATURE (IN K)
GUESS FOR TOTAL RADIUS (IN CM)
GUESS FOR TOTAL LUMINOSITY (IN LSUN)
WHAT IS YOUR OUTPUT FILENAME?
DO YOU WANT PULSATION OUTPUT? (Y/N)
The model will create an output file called output1 which should be similar to
modin001.out for this case.
In order to run this code you'll need initial guesses for Pc, Tc, R, L.
Initial guesses for different masses are given in Table 2.1 and 2.2 of Stellar
Interiors by C.J.Hansen and S.D.Kawaler, 1994 Springer-Verlag New York, Inc.
The initial guesses for 1,2,5 and 10 solar masses from these tables are as follows:
M/Msun log(L/Lsun) R*10^10 Tc*10^6 log(P_c)
1 -0.042 6.934 14.42 17.17
2 1.262 10.30 21.09 17.21
5 2.773 17.18 26.43 16.84
10 3.772 25.94 30.48 16.57
note that when you are asked for central pressure you have to convert the
initial guesses for logP_c to P_c.
In order to calculate models with different compositions/metallicity~0 you have
to do iterations. First calculate ZAMS model with solar composition (X=0.74,
Y=0.24, Z=0.02). Then use the FINAL MODEL from your output file for your first
model, and use the values for Pc, L, R, and Tc to calculate a model with
X=0.75 Y=0.24 Z=0.01. Then use the final model from this calculation as input
to another model with composition X=0.75 Y=0.249 , and then use the final model
from this calculation to calculate a model with X=0.75 Y=0.2499 (Z=0.0001). If
you want to play more with the code, you may continue to do more iterations to
get the metallicity down as much as possible.
ps: The model does not converge for the models with zero metallicity, but you
can push the models to approach zero metallicity by doing more iterations.
Last modified 3 November 2001