[Mesa-users] Red Giant Evolution

[Abha Vishwakarma]

Hi Jared,

Thank you so much for your response! Unfortunately it's not possible for me
to make the exact comparison as I do not have the files. So I was just
trying to do whatever I could, but I see that there's a lot more to it than
I thought. There is a lot to unpack in your email and I will try to
understand them one by one. I will go through the references you have
provided. Thanks again for such a detailed response!

Best,
Abha

On Wed, Jul 24, 2024 at 1:38 AM Jared Goldberg <
jgoldberg at flatironinstitute.org> wrote:

> Hi Abha,
>
> Speaking generally, this is not a well-defined problem for the MESA users
> list to answer easily, especially since we don't know what result you're
> trying to reproduce, nor where you're starting from. From your description,
> at best, one can speculate on some of the "obvious" ways that a star's
> lifetime and radius might be affected.
>
> It might be the case that you are just making 2 different stars. To make
> such a comparison, you need to make sure you're starting from the same
> place. Are you starting from the same or similar inlists? Are you using the
> same nuclear reaction network? Do you have the same values for mixing
> length alpha, winds, and core overshooting? Is everything else the same?
>
> There are many ways to affect the radius of the star, its evolutionary
> lifetime, etc, so it depends on how detailed a comparison you are trying to
> make and how large a discrepancy you are seeing to try to discern what the
> meaningful differences are and how to fix them. For example, the core mass
> might be affected by core-boundary mixing/overshooting. In general, with
> more overshooting, the larger the core becomes, which leads to higher
> luminosity and often shorter evolutionary lifetimes. Likewise, changing the
> nuclear reaction network may also significantly impact the onset of nuclear
> reactions including He burning. Changing the mixing length alpha will
> greatly affect the radius of the star, on the RSG branch typically larger
> alpha_MLT = smaller radii / larger effective temperature (more flux carried
> by convection = smaller R can give off the same L). Choosing a different
> convective mixing scheme (e.g. Henyey vs Cox vs TDC) and a different
> convective instability criterion (schwartzschild vs ledoux criterion) will
> also affect the radius and other properties. If you are using MLT++
> or superadiabatic reduction treatment, note that stronger superadiabatic
> reduction/MLT++ also causes hotter stars and smaller radii.
>
> A good reference on how wind prescriptions change the evolution of the
> star is Renzo+2017
> <https://ui.adsabs.harvard.edu/abs/2017A%26A...603A.118R/abstract>, and a
> reference for the impact of many other "stellar engineering" choices
> (including overshooting and nuclear reaction networks) on RSG properties is
> Farmer+2016
> <https://ui.adsabs.harvard.edu/abs/2016ApJS..227...22F/abstract>. For a
> bit more hands-on intuition-building exercises, I might highlight that we
> covered the impacts of various "stellar engineering" choices (including
> superadiabatic reduction, mixing length, and stellar winds) in this year's MESA
> (Down Under) School
> <https://sites.google.com/view/massive-stars-mesa-down-under/> put
> together with Ethan Winch, Annachiarra Picco, and Aldana Grichener. These
> labs are not exhaustive and don't focus so much on the onset of He burning
> or stellar lifetimes, but I think they do illustrate well the sensitivity
> of evolved massive star structure to "engineering" choices.
>
> Cheers,
> ~Jared
>
> On Tue, Jul 23, 2024 at 3:36 PM Abha Vishwakarma <
> abha.vishwakarma at niser.ac.in> wrote:
>
>> Hi Jared,
>>
>> Thank you for your reply. I am using MESA version 23.05.1. I am trying to
>> reproduce a stellar profile from a different work, and upon comparison I
>> found that my metal mass fraction near the core is much higher than
>> theirs, when I compare the models at the same star_age. The final radius of
>> the star is also less than their work. I have been playing around with the
>> wind schemes to see how they affect the evolution of the star, but I don't
>> fully understand them. It seems as though my star starts to burn Helium
>> earlier than their model. Please let me know if I am missing something
>> here.
>>
>> Thank you,
>> Abha
>>
>> On Wed, Jul 24, 2024 at 12:36 AM Jared Goldberg <
>> jgoldberg at flatironinstitute.org> wrote:
>>
>>> Hi Abha,
>>>
>>> A few questions:
>>>
>>> 1) What MESA revision are you using?
>>> 2) What do you mean by "much sooner"? When/where/under what conditions
>>> do you want or expect the star to start core He burning?
>>>
>>> In general, a 12Msun star will become a Red Supergiant, not a red giant,
>>> and it may even start core He burning while it is still crossing the
>>> Hertzsprung gap.
>>>
>>> Best,
>>> ~Jared
>>>
>>> On Tue, Jul 23, 2024 at 3:03 PM Abha Vishwakarma via Mesa-users <
>>> mesa-users at lists.mesastar.org> wrote:
>>>
>>>> Dear MESA Users,
>>>>
>>>> I am trying to evolve a 12 solar mass star with metallicity 0.01 to the
>>>> red giant phase. I am able to evolve it, but it is burning Helium into
>>>> metals much sooner than I want it to. I am not sure which controls I should
>>>> change to make sure this happens later. Is there any way I can achieve such
>>>> a model?
>>>>
>>>> Best,
>>>> Abha Vishwakarma
>>>> _______________________________________________
>>>> mesa-users at lists.mesastar.org
>>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>
>>>>
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