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

[Koushik Sen]

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
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