[Mesa-users] Setting subsolar/supersolar metallicity

[Amar Aryan]

Hello Ebraheem,

Thank you so much for detailing the process of setting the metallicity and
corresponding opacities.  I have a few more queries:

1) Can we use a single initial_zfracs (for e.g., asplund mixture by setting
initial_zfracs = 6) for both subsolar (for e.g., initial_z = 0.71d-2) and
supersolar (for e.g., initial_z = 2.82d-2) metallicity models?

2)  It is mentioned in section 3.1 of Jieun Choi et al. 2016 (MIST 1)
<https://iopscience.iop.org/article/10.3847/0004-637X/823/2/102>. "In other
words, [Z/ H] is computed with respect to Z = Z,protosolar = 0.0142, not Z
= Z,photosphere = 0.0134." However, when I looked in the
"mesa-r24.03.1/chem/public/chem_def.f90" file, it sets "real(dp), parameter
:: AGSS09_zsol = 0.0134d0" in line no 280. I think AGSS09 is from asplund
2009 (set by initial_zfracs = 6, in inlist_mass_Z_wind_rotation), so the
definition should be  "real(dp), parameter :: AGSS09_zsol = 0.0142d0."
 Please confirm if it is OK.

With regards,
Amar

On Tue, May 7, 2024 at 1:26 AM Ebraheem Farag <ekfarag at asu.edu> wrote:

> 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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