[Mesa-users] MLT++ for massive MS stars?
GM Mirouh
g.mirouh at surrey.ac.uk
Mon Dec 7 17:13:13 EST 2020
Dear Francis, and other users,
I am sorry for my belated reply to your advice here. I have finally made
some time to look into the ideas you suggested.
On 28/11/2020 20:31, Francis Timmes wrote:
> hi giovanni,
>
>
>> ... I just want to reach hydrogen depletion for these stars, ...
> ok. it would be useful to examine/show a few more diagnostics.
> what does the hr diagram look like from the start of the model
> to the point where convergence is not reached? what are the density
> and temperature profiles, especially in the outer regions?
I have made a couple of plots that I have attached here (they are pretty
basic): the HR diagram goes wild : after some evolution, the models seem
to jiggle around the proper values, until it goes visibly off track. In
the profiles, I indeed see a density inversion near the surface.
Let me know if you need more input (profile files, models, inlists...)
>
>
>> I have already written to you a little while ago about this ...
> presumably the "Massive stars and timestep management" thread you started on 12nov2020.
>
> my reply in the thread "Timestep and convergence problems for massive stars"
> may (or may not) contain a useful path forward for version 12778.
I have read that email with attention: you mention the idea of using
"use_simple_es_for_kap" to simplify the opacities and run far beyond
core H-depletion.
I can try and implement such a change, but I have a couple of questions :
* how did you estimate the relative importance of electron scattering to
the other contributions to opacity?
* to assess whether this shortcut changes the models by a lot, my plan
is to simply run a new track with simple electron scattering and
compare: do you have a better idea? would it make sense to turn that
control on only towards the end of the MS, so as to avoid the density
inversion but still include the "proper" physics as much as possible?
* you seem to specify this is for v. 12778: can I implement it in 12115
or is the control parameter you use new? is it available in the even
newer v.15140?
Thank you very much for the leads, and the possible solution,
Cheers.
--
Giovanni.
> fxt
>
>
>
>
>
>> On Nov 25, 2020, at 3:58 AM, GM Mirouh via Mesa-users <mesa-users at lists.mesastar.org> wrote:
>>
>> Dear all,
>>
>> I have already written to you a little while ago about this, and I am sorry to insist.
>> I am computing massive stars on the main sequence stopping once in a while to save a model (with mesa 12115). It works nicely for M<320Msun, but I am hitting all kinds of numerical difficulties for anything above that:
>>
>> 1) at some point during evolution, the timestep drops to almost nothing, and I think this is due to the luminosity hitting the Eddington limit (at Z=0.02, M=500, center_h1=0.45, my star has Teff=7600, logTcntr = 7.6 and logL=7.2 and evolves with log_dt=-0.3 ). It keeps running for a little while though, albeit very slowly, until...
>>
>> 2) my runs end up crashing with errors such as
>>
>> " retry 193406
>> mlt_partials(mlt_cv_var,mlt_gradT) 792 NaN
>> retry 193406
>> mlt_partials(mlt_cv_var,mlt_gradT) 792 NaN
>> backup 193406
>> mlt_partials(mlt_cv_var,mlt_gradT) 774 NaN
>> retry 193405
>> mlt_partials(mlt_cv_var,mlt_gradT) 774 NaN"
>>
>> Can anyone enlighten me about what is happening here? I am going out some interpolation table? is there something I can do?
>>
>> 3) I have tried playing with some numerical parameters, such as the starting timestep or the varcontrol value, and I have varied mixing parameters such as semiconvection or overshooting efficiencies, to no avail: the code as I have set it up seems to be digging a hole it cannot get out of.
>>
>> 4) Some people have mentioned MLT++ as a possible solution, while some others told me to avoid it like the plague. Recent events show people do not really avoid the plague, so I thought I could give MLT++ a try: I have turned "okay_to_reduce_gradT_excess = .true." but it does not seem to change much in terms of convergence (I have the exact same issues, only earlier on the MS). Do you know of a manual or do you have general advice for MLT++? Would it make sense to compute the MS as long as it works, save a model and then turn MLT++ on and proceed? Or maybe MLT++ is not the right approach at all?
>>
>> At this point, I just want to reach hydrogen depletion for these stars, and I am ready to make reasonable concessions about the accuracy of my models as long as I know what is happening in there.
>> I am sorry I don't know what kind of files to attach here, but I can provide anything you think can help you to help me. Thank you for any advice you can give me.
>>
>> Please take care,
>> Best.
>> --
>> Giovanni Mirouh
>>
>> _______________________________________________
>> mesa-users at lists.mesastar.org
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