[Mesa-users] Red Giant Evolution

[Jared Goldberg]

Indeed, code comparisons are hard work, especially if you don't know what
choices the other group/setup made! Good luck!

~Jared

On Tue, Jul 23, 2024 at 4:28 PM Abha Vishwakarma <
abha.vishwakarma at niser.ac.in> wrote:

> 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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