[Mesa-users] A question about delta_HR_limit

[Levi]

Hi Matteo,

Thank you very much for your time, I am not so confused now, and I will follow your suggestions to analyze it.

Thanks,
Levi



At 2022-03-29 21:56:57, "Matteo Cantiello" <matteo.cantiello at gmail.com> wrote:

Hi Levi,



Your rapidly rotating model is likely at the cusp between normal and quasi chemically homogeneous evolution. See e.g. Maeder 1987 (https://ui.adsabs.harvard.edu/abs/1987A%26A...173..247M/abstract),  Yoon  &  Langer  2005  (https://ui.adsabs.harvard.edu/abs/2005A%26A...443..643Y/abstract),  Paxton  et  al.  2013  (https://ui.adsabs.harvard.edu/abs/2013ApJS..208....4P/abstract). This is a threshold process,  with  the  amount  of  rotational  mixing  leading to very different solutions for the stellar structure.  When models are close to the transition rotational rate between normal and quasi chemically homogeneous,  results  are  sensitive to resolution and choices  of the internal physics. The  transition  line between  normal  and  quasi  chemically  homogeneous  evolution shown in e.g. Yoon & Langer 2006  for  models  with  different  metallicity  and  mass  (https://ui.adsabs.harvard.edu/abs/2006A%26A...460..199Y/abstract,  their  Fig. 3).

Quasi chemically homogeneous evolution also leads to larger cores, again because of internal mixing. Which explains your findings.



With that said, I don't know the details of how delta_HR_limit plays a role here, something you maybe can investigate a bit further (e.g. you can see that both models evolve quasi-chemically homogeneously until ~halfway on the main sequence). Maybe you can look at plots of rotational diffusivity and compositional gradients across that transition for the two models, and determine what is being affected differently and why.



Hope this helps,


Matteo


--

Matteo Cantiello - https://www.stellarphysics.org/
Research Scientist,  CCA, Flatiron Institute
Visiting Associate Researcher, Princeton University







On Tue, Mar 29, 2022 at 1:04 AM, Levi <mesa-users at lists.mesastar.org> wrote:

Dear Mesa users,



I had a very confusing experience when using MESA version r10398.

I was recently working on a set of models that went from zero age main sequence to core collapse, and in the process of this, I suddenly found that the delta_HR_limit option would greatly change the nature of the model. At the beginning I set a=b, the delta_HR_limit = 0.005d0 then the evolution trajectory moves towards the RSG of the 23Msun in the figure below, then I comment out it in the inlist, and the evolution trajectory moves towards the BSG such as 20Msun test. In addition, the helium core mass of the two models at the time of pre-collapse are 13.7 and 20.2 Msun, respectively.



I considered the initial surface speed of 600 km/s and the magnetic braking in the model but I don't know why the delta_HR_limit option would make such a big difference. 

I was very grateful for any information.



Thanks,

Levi





 


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