[Mesa-users] Minimum requirement for blue loops for supergiants

[Koushik Sen]

Hi Jeremy,

I am not an expert on Cepheid variable stars or the instability strip.
However, as far as I know, in the stellar models, it is mainly the mixing
length parameter that controls the temperature of the Hayashi line
(Kippenhahn & Weigert 1990).

I could not understand what you meant by very long simulations. You should
get blue loops in the core He-burning phase of the stars. So, your stopping
condition should be at least till the end of He burning. You can also share
the inlists you are using so that we can reproduce your models ourselves.

Cheers,
Koushik

On Wed, 10 Apr 2019 at 16:22, Jeremy Sakstein <sakstein at sas.upenn.edu>
wrote:

> Thanks Koushik!
>
> I just tried with alpha_semiconvenction = 10 and so far I am not seeing
> any loops. The Hyashi track also seems to be inside the instability strip?
> One thing I noticed is that the time-step is very small. Do I need very
> long simulations to see these loops?
>
> Cheers,
>
> Jeremy
>
> On Wed, Apr 10, 2019 at 4:31 AM Koushik Sen <senkoushik1995 at gmail.com>
> wrote:
>
>> Hi Jeremy,
>>
>> You need efficient semi-convection (alpha_semiconvection=1 or higher,
>> preferably 10) to get blue loops in this mass range. More efficient
>> semiconvection implies more mixing above the He-core, the hydrogen gradient
>> gets steeper and steeper H gradients favour more BSGs. The overshooting
>> parameter that you are using is fine. The lesser overshooting you use, the
>> smaller will be the He core formed, and you'll be more likely to get BSG
>> solutions, but even step_overshoot_f_above_burn_h_core=0.11 should be good
>> enough if you use alpha_semiconvection = 10. For more details on how
>> overshooting and semi-convection affects the evolution of massive stars,
>> you can have a look at this paper:
>> http://adsabs.harvard.edu/abs/2019arXiv190310423S.
>>
>> Hope this helps,
>>
>> Cheers,
>> Koushik
>>
>> On Tue, 9 Apr 2019 at 21:14, Jeremy Sakstein <sakstein at sas.upenn.edu>
>> wrote:
>>
>>> Hi Everyone,
>>>
>>> I've been trying to get blue loops for supergiant stars (13M and higher)
>>> by starting from a preMS model and evolving. My inlist works perfectly for
>>> lower mass stars but I don't see the loops for higher masses.
>>>
>>> I know that these loops are very sensitive to things like overshooting
>>> so I was wondering if anyone had an idea of what the minimum controls I
>>> need are to see these loops?
>>>
>>> I am using the default X and Y with initial Z=0.0006. At the moment, I
>>> am just turning the Ledoux criterion on and setting
>>> alpha_semiconvection=0.1. I tried several different mixing lengths and
>>> overshoot fractions (in the range 0.01 to 0.1) but so far I see nothing.
>>>
>>> I'd be very grateful for any help you can give.
>>>
>>> Cheers,
>>>
>>> Jeremy
>>> _______________________________________________
>>> mesa-users at lists.mesastar.org
>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>
>>>
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