[Mesa-users] Setting subsolar/supersolar metallicity

[Ebraheem Farag]

Hi Amar,

For deciding initial_y, It's typical to scale the abundances using a
scaling formulation like the one in section 3.1 of Jieun Choi et al. 2016
(MIST 1) <https://iopscience.iop.org/article/10.3847/0004-637X/823/2/102>.
Although you can choose to increase the value of Z at constant Y, just know
that these are not the same choices.

The initial_zfracs should not change. You are scaling the total abundance,
not the abundance of each individual isotope. The only time in which you
would change the initial_zfracs is when you are intentionally trying to
change the composition of the network at fixed Z. If you change the
initial_zfracs, you need to also be sure that you are using the correct
lowT, highT, and CO enhanced opacity tables that correspond to the desired
mixture you are choosing. In your case, the agss09 opacities are selected
in 'inlist common':

&kap
      ! OPAL asplund 2009 opacities, Zbase set in
inlist_mass_Z_wind_rotation
      kap_file_prefix = 'a09'    ! 'gs98' 'a09'  'OP_a09' 'OP_gs98'
      kap_CO_prefix   = 'a09_co' ! 'gs98_co' 'a09_co'
      kap_lowT_prefix = 'lowT_fa05_a09p'
      use_Type2_opacities = .true.

/ ! end of kap namelist

The default in mesa is initial_zfracs = 3 ! gs98 abundances, and the
default opacity tables are also for a gs98 mixture. We opt for the asplund
mixture in this test_suite.

Let this thread be a psa to all who read the mailing list: always ensure
you are using the correct values of initial_zfracs which corresponds to the
opacity/kap tables you have selected. Initial_zfracs can only be modified
at the beginning of a run when the model has a uniform mixture, so this is
not something you can change later.

-EbF

On Mon, May 6, 2024 at 7:07 AM Amar Aryan via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear MESA users,
>
> I am trying to evolve a subsolar (Z = Z_solar / 2 ) metallicity, 20 M_sun
> ZAMS star, up to the stage of the onset of core collapse by utilizing the
> "20M_pre_ms_to_core_collapse" directory in the latest MESA release,
> mesa-r24.03.1. By default, the directory is set for the solar metallicity
> with the following controls in "inlist_mass_Z_wind_rotation":
>
> &star_job
>    new_Z = 1.42d-2
>    new_omega_div_omega_crit = 0d0
>    initial_zfracs = 6 ! set to asplund 2009 abundance fractions
> / ! end of star_job namelist
>
> &kap
>    Zbase = 1.42d-2
> / ! end of kap namelist
>
> &controls
>    initial_mass = 20
>    initial_z = 1.42d-2 ! ! solar
>    initial_y = 0.2703d0 ! from asplund et al. 2009, solar.
>    Dutch_scaling_factor = 0d0
> / ! end of controls namelist
>
> If I set the initial metallicity to Z = Z_solar /  2, i.e., new_Z =
> 0.71d-2,  Zbase = 0.71d-2, and initial_z = 0.71d-2, how should I modify the
> corresponding "initial_zfracs" and "initial_y"?
>
> I noticed that there were no explicit options of "initial_zfracs" and
> "initial_y" in "inlist_mass_Z_wind_rotation" in earlier versions of MESA
> (e.g., in mesa-r23.05.1).  How is "intial_zfracs" different
> than "initial_z"? Please suggest.
>
> With regards,
> Amar
> _______________________________________________
> mesa-users at lists.mesastar.org
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