[Mesa-users] EOS/opacity (?) issues in proto-WDs

Thu Apr 18 11:10:58 EDT 2019

Hi all,

Thanks to Pablo, I was able to constrain the problem a little further. However, weeding out a few operator errors, I find that the problem persists. Since it’s been a week, a short recap: Using r11554, I am trying to model low mass helium stars losing mass via RLOF to a binary companion, and I want to follow the evolution as far as possible. The problem is this: Once the model gets to a mass below 0.2 Msun, the hydro solver runs into numerical problems. Specifically, the gradT profile seems to give unphysical and unstable results. Please find attached four consecutive profile plots (these issues had been going on for a while at that point) just prior to the model crashing:

I realize that these are calculated with a rather large timesteps, but I find that neither reducing the timesteps nor refining the grid has any appreciable effect.

(There may also be an issue with convection.)

Basically, I am still at a loss on how exactly to deal with this. Could this be related to the eos? I am again attaching the initial model and inlists.

Best wishes

Patrick

> On 12. Apr 2019, at 15:11, Patrick Neunteufel <neunteufel at astro.uni-bonn.de> wrote:
> 
> Hi Pablo, 
> 
> Thanks for the help so far. I did a few more tests of my own and introducing a shallower composition gradient by including semiconvection does not seem to solve the issue. Apparently, the problem manifests as a convergence issue in the hydro solver once RLOF affects former burning regions. My earlier assumption that degeneracy may have something to do with it seems to be in error.
> I also forgot to include the initial orbital separation of the plot I sent you yesterday, in case you want to reproduce the error: initial_separation_in_Rsuns = 0.556062     
> The rest of the inlists are as posted on Wednesday.
> 
> Best
> 
> Patrick
> 
>> On 11. Apr 2019, at 18:43, Patrick Neunteufel <neunteufel at astro.uni-bonn.de <mailto:neunteufel at astro.uni-bonn.de>> wrote:
>> 
>> Yes, I assumed that the composition discontinuity could be part of the problem. As for magnetic braking: Thanks for pointing this out. I momentarily forgot that magnetic braking is enabled by default.
>> 
>> Anyhow: running the same experiment with a lower mass donor star, magnetic braking disabled and closer initial orbital separation (see final plot preceding the crash below) results in the same problem.
>> 
>> Best
>> 
>> Patrick
>> 
>> <He-star.mod>
>> 
>> 
>> <grid1003670.png>
>> 
>> 
> 

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