[Mesa-users] Setting subsolar/supersolar metallicity

Tue May 7 16:53:27 UTC 2024

Hi Amar,

1 - Yes, I would recommend using identical 'intial_zfracs' and not thinking
further about it unless you have plans for adjusting the initial network
composition.

2 - There are two mixtures communicated in Asplund et al. 2009, one is the
photospheric mixture, and the other is meteoric mixture (there is some
overlap for individual elements). MESA adopts the photospheric mixture not
the meteoric mixture, therefore the total metallicity for the reference
initial_zfracs = 6 is lower "0.0134"(photospheric) than it would otherwise
be "0.0142" (meteoric). This is a result of heavy element diffusions
(gravitational settling) of heavier elements over the lifespan of the Sun.

MESA adopts the current solar photospheric mixtures, and it is a normal
practice to scale the value of 0.0134 up to 0.0142 to achieve metal mass
fractions that are approximately equal to the meteoric values. This is in
effect what is being communicated in the MIST 1 paper.

-EbF

On Mon, May 6, 2024 at 8:54 PM Amar Aryan <amararyan941 at gmail.com> wrote:

> 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://urldefense.com/v3/__https://iopscience.iop.org/article/10.3847/0004-637X/823/2/102__;!!IKRxdwAv5BmarQ!YhnrtvzGVVoiMGnHA27SCzWlR4E3PBXVDzostU9iJYMKwYmwyS3jE7hsgBO4HdxNhgkYA24DvfYUD7CbkpNSb37rKQ$>
> . "In other words, [Z/ H] is computed with respect to Z = Z,protosolar =
> 0.0142, not Z = Z,photosphere = 0.0134." However, when I looked in the
> "mesa-r24.03.1/chem/public/chem_def.f90" file, it sets "real(dp), parameter
> :: AGSS09_zsol = 0.0134d0" in line no 280. I think AGSS09 is from asplund
> 2009 (set by initial_zfracs = 6, in inlist_mass_Z_wind_rotation), so the
> definition should be  "real(dp), parameter :: AGSS09_zsol = 0.0142d0."
>  Please confirm if it is OK.
>
> With regards,
> Amar
>
> On Tue, May 7, 2024 at 1:26 AM Ebraheem Farag <ekfarag at asu.edu> wrote:
>
>> Hi Amar,
>>
>> For deciding initial_y, It's typical to scale the abundances using a
>> scaling formulation like the one in section 3.1 of Jieun Choi et al.
>> 2016 (MIST 1)
>> <https://urldefense.com/v3/__https://iopscience.iop.org/article/10.3847/0004-637X/823/2/102__;!!IKRxdwAv5BmarQ!YhnrtvzGVVoiMGnHA27SCzWlR4E3PBXVDzostU9iJYMKwYmwyS3jE7hsgBO4HdxNhgkYA24DvfYUD7CbkpNSb37rKQ$>.
>> 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
>>>
>>> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!IKRxdwAv5BmarQ!etPLZ2NqREX9P3DqpN4pYzvDn4q5bXOY7MpZwKeShRNbwtT4vPB2rrSf0pcEtyjAndF8o22ATahSVRXwIjHGkMAlKXgSXQ$
>>>
>>>
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