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

[Torres, Guillermo]

Hi Matteo,

Your comments are very helpful. Let me look into them, and I will also try
the experiments you suggested. I'll also look into the literature some more.

Thanks,
Willie

On Thu, Jan 23, 2025 at 5:17 PM Matteo Cantiello <matteo.cantiello at gmail.com>
wrote:

>
>> This is true. But I also wonder why the PARSEC models for a similar mass
>> and initial rotation *do not* reach critical rotation at the blue hook,
>> whereas MESA does. I've been assuming that PARSEC manages to get rid of
>> angular momentum more efficiently at this mass and initial w/w_crit,
>> somehow. Still, I agree that having the right observations would be very
>> useful.
>>
>>
> Ok, that's a well defined question and worth looking into it. I am not a
> PARSEC expert, but I have used other codes than MESA that include the
> physics of rotation. I'll assume you have double checked that the models
> you are comparing start rigidly and with the same rotation rate, as this
> can depend on how rotation is initialized. With that out of the way, one
> issue that matters a lot when it comes to reaching critical rotation is how
> angular momentum is transported in the model. It is easy to understand why:
> stars that have efficient angular momentum transport stay ~rigidly rotating
> during the main sequence.  While models with weaker transport develop some
> degree of differential rotation. Now this is important because it may
> change the ability of stars to reach breakup: if more angular momentum is
> stored in the core, the envelope can rotate more slowly.
>
> The most efficient sources of coupling during the MS in MESA are magnetic
> torques from Tayler-Spruit dynamo fields, and meridional circulation
> (Eddington Sweet). I just looked at one PARSEC paper from 2022 and their
> rotating models do not have magnetic torques.  While this is disfavored by
> asteroseismic observations that point to efficient angular momentum
> transfer in stars, in order to compare to the PARSEC models you correctly
> seem to have turned ST off in your inlist. However, if your goal is not a
> direct comparison I would argue you should have magnetic torques on.
> PARSEC then includes Eddington Sweet and Shear, while MESA has those plus
> a few more (all described in the controls and the second instrument paper).
> The formulation of the shear diffusivity in PARSEC is different than in
> MESA (Talon & Zahn 1997 <-> Heger et al. 2000). But I doubt this should
> make much difference. I would then for sure test turning off SH and GSF as
> well. All in all I would test with:
>
>     D_ST_factor = 0.0
>     D_SH_factor =  0.0
>     D_GSF_factor = 0.0
>     D_ES_factor =  1.0
>     D_SSI_factor = 1.0
>     D_DSI_factor = 1.0
>
> In order to see if you get results more similar to PARSEC. And I would run
> with
>
>     D_ST_factor = 1.0
>     D_SH_factor =  1.0
>     D_GSF_factor = 1.0
>     D_ES_factor =  1.0
>     D_SSI_factor = 1.0
>     D_DSI_factor = 1.0
>
> for your science runs.
> Cheers,
>
> Matteo
>
>
>>
>>
>>
>>> 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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