[Mesa-users] Mesastar Question: Setting Initial CO Abudance Enhancements

[Frank Timmes]

hi kayla,

i suspect you'll need to set a precise initial composition. to do so, following https://docs.mesastar.org/en/release-r24.03.1/reference/star_job.html#file-for-uniform-xa , one goes something like

! set specific mass fractions 
       set_uniform_initial_xa_from_file = .true.
       file_for_uniform_xa = 'example.dat'

where example.dat is attached. the mass fractions listed in file_for_uniform_xa should sum to unity and include every isotope in chosen reaction network. in example.dat the isotopes listed are for a 79 isotope network.

fxt




> On Aug 1, 2024, at 12:48 AM, KAYLA MARTIN via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Hi, 
> 
> This is my first post on the mesa user list.
> 
> I am creating a model with X=0.732, Y=0.26, and Z=0.008, with the chemical composition mixture of Grevesse & Sauval (1998). In this model, I need to set [O/Fe]=+0.2 (equivalent to [O/H]=-0.1 or X(O)=0.0042), though I cannot see a clear way to implement this in my model.
> 
> I have attempted to create an opacity table using the AESOPUS tool <http://stev.oapd.inaf.it/cgi-bin/aesopus>, though it seems this only applies at 'low temperatures' (the tool won't let me set higher than Teff=log3.7)? Further, the implementation of the tables generated from this tool are unclear -- the related instructions in mesa have outdated information (last updates ~2013), and contains variables that no longer exist in more recent mesa versions (e.g., $MESA_DIR/kap/preprocessor/README_creating_OPAL_type2_tables notes inlist variables such as Zfrac_O). 
> 
> Any guidance on how to correctly specify the initial oxygen abundance in my model with a gs98 reference solar composition will be very helpful. 
> 
> Thanks!
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