[Mesa-users] Issue with rotation in MESA r22.11.1

[Matteo Cantiello]

Hi Willie,

On Thu, Jan 23, 2025 at 3:48 PM Torres, Guillermo <gtorres at cfa.harvard.edu>
wrote:

> Hi Matteo,
>
> Thanks for the quick reply.
>
> On Thu, Jan 23, 2025 at 3:09 PM Matteo Cantiello <
> matteo.cantiello at gmail.com> wrote:
>
>> Hi Willie,
>>
>> It seems like you’re suggesting that the shape of the evolutionary track
>> is ‘odd,’ but I think it’s more accurate to say that it differs from the
>> PARSEC model. This difference isn’t entirely surprising, as the MESA
>> calculation reaches critical rotation, while the PARSEC model does not.
>>
>
> Yes, I certainly agree with that.
>
> There could be a variety of factors contributing to the discrepancy --
>> such as differences in initial conditions, the treatment of mixing, or
>> angular momentum transport -- and it’s difficult to pinpoint the exact
>> cause based solely on the inlist and plot you’ve provided.
>>
>> If the goal is to reproduce the PARSEC results, you’ll want to ensure the
>> physics and initial conditions in your MESA setup match those in the PARSEC
>> calculation as closely as possible. Once that alignment is achieved, if
>> differences still persist, it would be ideal to run both PARSEC and MESA
>> side by side and compare results throughout the evolutionary stages. This
>> approach might help identify where the divergence arises.
>>
>
> My goal is not really to reproduce the PARSEC results exactly or
> quantitatively (e.g., in terms of luminosity or temperature), as there are
> probably so many differences in the physics of the two codes that it would
> be unlikely one could do that. Instead, I was simply struck by the
> morphology of the blue hook in MESA, which is so different from the
> 'familiar' shape seen with PARSEC, as well as the few other models for
> rotating stars that I have seen in the literature.
>

Have you compared to models in the literature that reach critical rotation
like yours?

>
> Ideally one would want to run PARSEC and MESA in parallel, as you suggest,
> though this is more easily said than done, and would obviously require
> access to the PARSEC code. In any case, from feedback from others, it
> appears I'm not the first to encounter this problem,
>

I am not sure it is a problem. It would be a problem if we had measurements
of stars with well defined parameters that are critically rotating at
H-exhaustion and show a very different HRD position as compared to your
calculations. But I don't think we have that constraint.


> and it would seem prudent to ignore the part of the tracks that come so
> close to breakup.
>

I think it is prudent to assume that we do not have a great grasp of the
physics of breakup and how to treat the stellar surface layers and mass
loss at critical rotation.
But I don't think ignoring the track just because it doesn't look like a
track of a non-critically rotating star is warranted.
I understand that there is a preference to select for tracks that look
smooth and more similar to the ones published in stellar physics books (I
certainly do not like to publish HRDs with messy tracks, although I have),
but again I would stress that unless we have clear observational evidence
that favor a numerical model over another, selecting for aesthetic is not a
great way to proceed. It is conceivable that stars in short evolutionary
phases and undergoing some extreme process (like critical rotation) might
have very complicated tracks.

My two cents,
Matteo



> Willie
>
>
>>
>> --
>> Matteo Cantiello - https://www.stellarphysics.org/
>> Research Scientist,  CCA, Flatiron Institute
>> Visiting Associate Researcher, Princeton University
>>
>>
>> On Thu, Jan 23, 2025 at 2:53 PM Torres, Guillermo via Mesa-users <
>> mesa-users at lists.mesastar.org> wrote:
>>
>>> All,
>>>
>>> I am using MESA r22.11.1 to model the evolution of a rapidly rotating
>>> star of 5.04 solar masses (initial w/w_crit = 0.55), and I'm finding an odd
>>> shape for the evolutionary track in the blue hook region, as the star is
>>> contracting. During this phase, I see the model reaching very high values
>>> of w/w_crit up to the limit of 0.99, and as it approaches that value, the
>>> morphology goes haywire, at least compared to a similar track from the
>>> PARSEC v2.0 series (see figure attached, with the odd part highlighted in
>>> red). I'm wondering if this really is an issue with the physics in MESA, or
>>> just that I don't have the right controls in my inlist. It appears the star
>>> would need to get rid of more of its angular momentum to avoid this, but
>>> evidently it is not doing that with the controls I am using. I attach my
>>> inlist for reference. The pre-main-sequence part is computed separately. I
>>> would be thankful for any suggestions.
>>>
>>> Willie
>>> _______________________________________________
>>> mesa-users at lists.mesastar.org
>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>
>>>
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