[mesa-users] isotopic initial abundances

[Ehsan M. <e.m...@gm...>]

Dear mesa developers and users,
First of all, let me wish you a wonderful and flourishing 2015.

I have a question regarding initialization of isotopic abundances.
There are currently (using v.7280) two possibilities to specify the initial mixture. 

(1). The first is to use pre-defined abundance list, like
      initial_zfracs = 3
looking into /chem/public/chem_def.f, the element abundances in number fraction (in spectroscopic notation) are defined there. E.g. 
         GS98_element_zfrac(e_H)=12.00
         GS98_element_zfrac(e_He)=10.93
         GS98_element_zfrac(e_C)=8.52
         …
Clearly, the abundance of isotopes of carbon are not specified here. However, if the burning net requires to incorporate, e.g. C13, then C12 and C13 (over some function calls) will receive non-zero shares of initial C abundance. Thus, there are some function calls taking care of this that I still do not know.

(2). the other possibility is providing a list of elements with their mass fractions as a two-column file (and making sure they sum up to unity). E.g. 
      file_for_uniform_xa = ‘user-defined-file’
Here, if the user would not provide the initial isotopic abundances -- of e.g. C13 —, then it is kept zero, and some burning branches of e.g. CNO will be ill-behaving.

For now, I strongly prefer the 2nd case, i.e. supplying my own initial element abundances, without specifying the isotropic ratios. Something like the attached file. But, I would like to be able to make corrections to the input list so that required isotopes would have non-zero initial abundances, and all burning sub-branches would be activated.
Does anybody know how to do this from extras_startup in run_star_extras?

Best regards
Ehsan.