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

Jeremy Sakstein sakstein at sas.upenn.edu
Wed Apr 10 10:22:31 EDT 2019

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?



On Wed, Apr 10, 2019 at 4:31 AM Koushik Sen <senkoushik1995 at gmail.com>

> 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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