The Input and Output of STARS

This page is almost finished, just has a couple of gaps.

Here, the input model and the output files of the code are discussed.

MODIN (fort.25)

This file contains the input model that the code will start to evolve when run. The first line of the code contains the following parameters:


SM is the mass, in solar units of the star being evolved.
DTY is the inital size of the timestep that will be used.
AGE is the current age of the model. Note that if you take a model from a previous run, you may wish to reset the age to zero. It has no effect on the calculations.
PER is the period of the binary system in days. The code treats all models as if they are part of a binary system. If you only wish to evolve a single star, then set this variable to something large (1020 is my usual choice).
BMS is the total mass of the binary; it must always be larger than the mass of the object star (2000 is a convenient choice for single star evolution).
EC is the rate of energy generation used for evolving back up the Hayashi track to create pre-MS stars. For normal evolution, it is set to zero.
NH is the number of mesh points in the current model.
NP is the number of models that is desired for the current run.
NMOD is the model number of the current model. If you are starting a new run, you may wish to set it to zero (this is not important, as it doesn't affect the calculation).
IB is the number of the star in a binary system (i.e. it's either 1 or 2). It affects the boundary conditions being used at the surface - for stars losing mass, IB=1 and for stars accreting, IB=2. For single star evolution it is set to 1.

The remaining numbers in this file are the actual details of the model. There are 11 independent variables recorded, and there should be NH rows of numbers. The variables, in the order of the columns that appear, are:

  1. ln f - a quantity closely related to electron degeneracy
  2. ln T - temperature in Kelvin
  3. X16 - the abundance of 16O
  4. ln m - mass in units of 1030kg
  5. X1 - the abundance of 1H
  6. C - the gradient of the mesh spacing function, Q(P,T,m,r). It does not depend on K, though it does vary with time. It is in effect an eigenvalue.
  7. ln r - the radius in units of 109m
  8. L - luminosity in units of 1026W
  9. X4 - the abundance of 4He
  10. X12 - the abundance of 12C
  11. X20 - the abundance of 20Ne

After these NH rows, come another NH rows. These are the changes made to the variables at the last timestep. In some cases, they will all be zero. It is important to copy all the numbers from the MODOUT file if you wish to start from exactly the same point as the last evolutionary run.

MODOUT (fort.23)

Output models from the code are written to here. The frequency at which this occurs is controlled by the value of NSAVE in DATA. The output format is the same as described above for MODIN. Any of the models written here can be placed into MODIN to be used in a subsequent run.

OUT (fort.22)

This file is useful as a reference for what is going on as a star evolves. The file starts with a copy of the data block used for the star's evolution. Below this is a print out of the first line of MODIN, so you know exactly where the model started from. The structure of the remaining output depends on the values that were chosen in DATA. Typically, the code will produce a short four line summary of the model (the frequency depends on the value of NWRT4), like the one below:

1.9953 5.366916000E+00 1.222E+07 1.263E+16 1.881E+03 0.000E+00 0.00000 0.97804 0.00298 0.01223 0.00103 0.00187 0.00076 10.370 5.7767 8.0669 cntr
0.4335 1.064366908E+09 3.962E+04-2.103E+01 1.580E+04 1.205E+02 0.66676 0.31323 0.00224 0.00255 0.00954 0.00184 0.00076 -17.475 -8.3377 3.5637 srfc
0.0000 1.0413    0.9143 2000.0000 0.000E+00 1.612E-33 0.0003 0.00000 0.97804 0.00298 0.01223 0.00103 0.00187 0.00076 10.370 5.7767 8.0669 Tmax

The first column contains the number of the model (in this case 579), then the mass of the star being evolved, in solar units (1.9953). The next number is the location in mass of the boundary of the hydrogen burning shell, and the last is the location in mass of the boundary of the He-burning zone. In the second column, we have the current timestep of the model and below it the current age of the model - both in years. The two numbers below these are the masses of H and He in the star, in solar units. The next column gives the nuclear and Kelvin-Helmholtz timescales in years, and the mass of the binary system in solar units. In column four, we find the period of the binary system in days, the difference between the stellar and Roche Lobe radii (in units of the stellar radius) and the rate of mass transfer. Next come two columns giving information about the luminosity of the system. First up are the luminosities from hydrogen, helium and carbon (actually, any nuclear burning that isn't H or He!), followed by the thermal and nuclear luminosities. The units are ? and the m at the base of this column is the mass location of the region of maximum temperature. The remaining entries give the abundances of nuclear species at the three points noted in the far right column.

After this block comes another 4 lines proving information about the model. It will take a form something like:
0.00000.197 -0.197 0.437 -0.437 1.995 -1.995 0.000 0.000 0.000 0.000 0.000 0.000 -3.4512 0.1076 2.4109 2.0111 3.2299 579
131 199 177 -177 82 -82 3 -3 0 0 0 0 0 0
0.4336 0.0003 0.0000 0.1038 0.4330 0.4341 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 1.187E+07 1.705E+09 6.304E-24
131 199 0 182 136 122 0 0 0 0 0 0 0 0 0Inf

On the first line, the first number is the mass interior to the point at which carbon burning occurs. The next twelve are the masses interior to the points at which the model changes from convective regions to radiative regions (and vice versa). The next 3 numbers are:(??). Then comes the base-10 log of the radius in solar units, followed by the base-10 log of the luminosity in solar units. The final number is the number of the model.

On the second line, the first number is the mesh point marking the H-shell burning boundary. The next number is the same quantity, but for the He-burning region. The last 12 numbers of the second line give information on where the boundaries between convective and radiative regions are. Boundaries between convective and semi-convective regions are marked by negative signs; convective/radiative boundaries have no sign.

On the third line, the first three numbers are the mass-locations of the points of maximum hydrogen, helium and carbon energy generation. The next 12 numbers are the mass-locations of the boundaries of burning regions. The final three numbers on this lines are the values of the energy generation rates for hydrogen, helium and carbon respectively, at their maximum points.

On the last line, the first three numbers are the the mesh point numbers of the points of maximum hydrogen, helium and carbon energy generation. The next twelve numbers are the mesh point numbers of the location of burning shell boundaries. The last value is d(log r)/d(log m).

Every NWRT1th model, the code will output details of the model. The printed details are selected via ISX in DATA.

PLOT (fort.10)

The code writes select details of each model to this file, so that such things like evolutionary tracks can be plotted. The file contains the following information, in this order:

Last modified: Mon May 31 11:42:47 2004
by R. Stancliffe