CHE_EVO

 

.. .is a simple chemical evolution program written by G.L.Granato to generate input SF histories for GRASIL. Of course you could also consider the possibility to use another code, provided you write its output in the same format as the file .sf produced by CHE_EVO. Also in this case the study of CHE_EVO and its source code will be helpful.

For an introduction to the equations and astrophysical concepts related to the code, read this small document (or its PostScript version, if your browser do not display correctly the equations) taken form Laura's PhD thesis. After this reading you will understand more easily the following brief '(very smart) user manual' and the comments written in the sample input parameter file we provide.

Basically the star formation rate (SFR) history tabulated by CHE_EVO is the result of the linear superposition of two components, one coming from a Shmidt-type law which connect the SFR to the gas content, and another giving a SFR directly as a function of time (two possibilities: constant between two ages or exponential decay). Each of the two components can be switched off, to obtain pure 'Schmidt' or pure 'analytical' chemical evolution. The true superposition of the two has been used by us to reproduce the SEDs of starburst galaxies such as M82.

 

Syntax:

The program is invoked, similarly to GRASIL, by the following command:

che_evo {mod_nam} [par1=value1] [par2=value2]...

where the parameter mod_nam is a string (maximum 10 characters) used by the program to assign file names  for input and output, as described below. The executable che_evo and the libraries it uses may well reside in a different directory than mod_nam.* files. In this case simply give the full path before grasil in the above command. The command line parameter within {} is compulsory, while those within [] are optional. The strings par1, par2 etc stand for the names of the parameters which are set in the file mod_nam.che (see below). Whenever new values are given in the command line (value1, value2 etc.), they supersede those written in the .che file.

Input:

mod_nam.che: file with all the input parameters defining the chemical model. Note that the values of the parameters given in the mod_nam.par file may be overridden by specifying different values in the command line, with the syntax par=value, where par is the name of the parameter you want to alter, and value its new desired value. You can modify as many parameters as you want in this way.

Output:

mod_nam.sf: file with the star formation and chemical enrichment histories of the model.

Now is time for you to look at the sample .che file where more explanations are given.

The CPU time required by CHE_EVO depends on several things, first of all how long the model is evolved. For a typical model, evolved for ~ 10 Gyr, it may be of the order of 100 s.

Download

Both executables and F90 source are given. Note however that there are calls to "Numerical Recipes in Fortran 90" routines, which, due to copyrights, are not distributed here.

Download and decompress in the same directory the following files:

 

[NOTE: sometimes due to incompatibilities between windows created texts then used with linux, carriage-return symbols are present in the ascii files in celib.tar.gz or celib.zip for pc linux. In this case do e.g.

> dos2unix mod_name.che

and similar with the other input files, in order to eliminate those symbols.]

 

For PC-Windows:

  1. celib.zip (libraries of stellar lifetimes and ejecta, examplel.che and source code)
  2. che_evo.zip (CHE_EVO executable)

For Alpha-Digital Unix:

  1. celib.tar.gz (or celib.zip provided you know how to decompress. For instance decompress on a PC then ascii ftp)
  2. che_evo.gz (CHE_EVO executable)

For PC-linux (see note below):

  1. celib.tar.gz (or celib.zip provided you know how to decompress. For instance decompress on a PC then ascii ftp)
  2. che_evo_linux.gz (CHE_EVO executable)

After decompression, give the command "che_evo examplel" in the same directory (on UNIX you could need to give before "chmod +x che_evo"). If everything is OK, CHE_EVO will run the model described in the input file examplel.che. On a reasonable present day CPU, it will require no more than 100-200 sec to complete examplel.sf .

Recall that CHE_EVO can be run in any other directory giving the full path of the executable. It requires input file .che in the working directory.

NOTE: the compiler used under linux produces poor executables with respect to that used under windows when "assumed shape arrays" are used. This is often the case for numerical recipes in f90 routines. As a result on the same CPU the computing time of CHE_EVO is a factor 5 longer under linux! The same was true for GRASIL as well, but now we optimized it in order to get almost equal computing times (still 30% longer). In the next future we hope to have time to fix the problem with CHE_EVO as well.