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 kilic@astro.as.utexas.edu

EXAMPLELet'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 % a.out Then the program will ask: THE TOTAL MASS IS (IN MSUN) 1. X(Hydrogen) AND Y(HELIUM) ARE .74 .24 GUESS FOR CENTRAL PRESSURE (IN CGS) 1.483e17 GUESS FOR CENTRAL TEMPERATURE (IN K) 1.449e7 GUESS FOR TOTAL RADIUS (IN CM) 6.93e10 GUESS FOR TOTAL LUMINOSITY (IN LSUN) .9 WHAT IS YOUR OUTPUT FILENAME? output1 DO YOU WANT PULSATION OUTPUT? (Y/N) 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.HAVE FUN