[mesa-users] isotopic initial abundances

Ehsan Moravveji e.moravveji at gmail.com
Fri Jan 9 15:45:22 EST 2015


Dear mesa-users, Dear Bill,
Few days ago, I asked about how isotopic abundances are allocated based on their initial elemental abundance. For another minor question, I’m going to continue the thread… 

On Jan 3, 2015, at 11:53 PM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> 
> On Jan 3, 2015, at 10:05 AM, Ehsan Moravveji wrote:
> 
>> Dear mesa developers and users,
>> First of all, let me wish you a wonderful and flourishing 2015.
> 
> Thank you!  ;D  Same to you.
>> 
>> 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.
> 
> track it down --- the trail starts in star/job/run_star_support.f90 with a call on star_set_standard_composition; that is in star/public/star_lib.
> that calls set_standard_composition in adjust_xyz. (in star/private).
> that call get_xa_for_standard_metals which in turn calls one of the chem routines such as GN93_element_zfrac to get the element fractions.
> then it calls get_xa to set the isotope mass fractions.  after doing the h and he isotopes, it calls adjust_z_fractions to finish the job.
> it calls the chem function lodders03_element_atom_percent to get info about abundances of isotopes in the solar system.
> the mass fraction for each element is then divided among the isotopes of that element in the current net in proportion to their solar system abundances.
> 
Bill kindly directed my to /chem/data/lodders03.data, which lists the isotopic abundances of most of the required isotopes for the burning nets.
Yet, there are still few of them which are not listed in Lodders (2009), but are needed for CNO sub-chains, like Be7, N13, O15, etc.
Although these catalysts are produced through CNO cycles, if their initial abundance be non-zero, they can contribute to the energy production from the beginning.
I wonder how else it is possible to give these isotopes non-zero initial abundance? I mean what abundance ratios shall I assume for these?

That’s it!
Best wishes
Ehsan.


> 
>> (2). the other possibility is providing a list of elements with their mass fractions as a two-column file
> 
> No.  That is not correct.   It is not a list of elements.   It is a list of isotopes with a mass fraction for each.  
> the list must be a subset of the isotopes in the current net and the sum must be 1.
> 
> track it down -- starting from star/job/run_star_support with a call on star_uniform_xa_from_file; that's in star/public/star_lib.
> that calls set_uniform_xa_from_file in adjust_xyz.  
> that reads the file by calling read_xa and then stores the mass fractions by calling set_uniform_composition.
> 
> 
> -b

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