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

Jeremy Sakstein sakstein at sas.upenn.edu
Wed Apr 10 14:13:02 EDT 2019

Thanks Koushik!

I was getting the hook but not the loop. I think it must have been the
z_base thing. For some reason my code crashes unless I increase the
mesh_delta_coefficient but that's not a major issue for my purposes.

Thanks for your help!



On Wed, Apr 10, 2019 at 11:52 AM Koushik Sen <senkoushik1995 at gmail.com>

> Hi Jeremy,
> I ran your inlist in Mesa r10108. I have attached my plot with the mail.
> 1) You need to set Zbase equal to initial_z in the inlist since you are
> using Type2opacities.
> 2) I ran two models: one with alpha_mlt = 1.73 and the other 1.3. The
> models are till the end of He-burning. I do see a blue loop for 1.3 and a
> blue hook for 1.73.
> It seems to stop due to too many backups high up the Hyashi track.
> I did not get any problems like this though, the code ran smoothly.
> Cheers,
> Koushik
>> On Wed, Apr 10, 2019 at 10:40 AM Koushik Sen <senkoushik1995 at gmail.com>
>> wrote:
>>> 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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