[Mesa-users] STELLA calculation fail to converge for massive stars

[Jared Goldberg]

Hi Amar,
>
>
> a) I could notice that after finishing the *inlist_to_si_burn* stage in
> the *example_make_pre_ccsn* directory, the model fails to achieve the
> prescribed temperature (lgT) of 9.85 while running *inlist_to_lgT9.9*, so
> I decreased the limit to 9.61 and rerun the calculation. This time the
> evolution successfully proceeded. Please note that even a lgT of 9.62 was
> not achieved so I tried 9.61.
>
Sounds like the model never made it to the end of Si burning/the generation
of the Fe core, which should happen around log(Tcenter) = 9.9.


> b) Thereafter, the shock is evolved using the *example_ccsn_IIp* directory
> with few changes like, in *inlist_infall*, we required to change the *remove_initial_center_by_entropy
> = 19.6*   (default value is 4). Few timestep adjustments were also done.
> Then the calculation proceeded nicely and the *mesa.abn* and *mesa.hyd* (please
> see attached ) files were successfully created. Please take a look to
> *inlist_shock_part5* also.
>

This makes sense, given point (a). The entropy profile tells you where the
various core boundaries are, and the Fe core boundary crosses an entropy
value of 4. So by going up in entropy you're effectively removing more than
what would have been the Fe core, likely closer to the CO boundary.

c) These two files were then used as input for STELLA calculations. The
> STELLA calculation started nicely but seems that it fails to converge. On a
> 16GB RAM and octa-core processor machine, the calculations ran up to a
> period of more than 24hours but the light curve only up to 7days was
> produced with the calculation still going on.

Since this is a fundamentally STELLA issue, I'm happy to discuss as a
MESA+STELLA user but note that it seems like everything you're doing in
actual MESA is working.
It might just be the case that more runtime is simply what STELLA needs.
Ultimately, you are solving radiation transport through a lot of
slow-moving, dense material, with an order of magnitude more mass than a
normal IIP calculation. Things to consider: What are the velocities you
get? What explosion energy do you use? What do you set for the innermost
velocity (your fallback cut)? Do you get any fallback (see Appendix D of MESA
instrument paper V
<https://ui.adsabs.harvard.edu/abs/2019ApJS..243...10P/abstract> and
appendix A of this paper
<https://ui.adsabs.harvard.edu/abs/2019ApJ...879....3G/abstract>)? For a
400 Msun star, the inner ejecta definitely could be causing the
computational slowdown.

Cheers,
~Jared

On Sun, Dec 13, 2020 at 10:37 PM <amar at aries.res.in> wrote:

> Dear MESA team,
>
> MESA Version : 11701
>                   OS : ubuntu 20.04
>
> I am trying to study the evolution of very massive stars (in particular
> 400M_sun without any rotation and mass loss) with the help of MESA. I could
> evolve the star up to the stage of core-collapse. Here, I wish to discuss
> and understand few points :
>
> a) I could notice that after finishing the *inlist_to_si_burn* stage in
> the *example_make_pre_ccsn* directory, the model fails to achieve the
> prescribed temperature (lgT) of 9.85 while running *inlist_to_lgT9.9*, so
> I decreased the limit to 9.61 and rerun the calculation. This time the
> evolution successfully proceeded. Please note that even a lgT of 9.62 was
> not achieved so I tried 9.61.
>
> b) Thereafter, the shock is evolved using the *example_ccsn_IIp*
> directory with few changes like, in *inlist_infall*, we required to
> change the *remove_initial_center_by_entropy = 19.6*   (default value is
> 4). Few timestep adjustments were also done. Then the calculation proceeded
> nicely and the *mesa.abn* and *mesa.hyd* (please see attached ) files
> were successfully created. Please take a look to *inlist_shock_part5*
> also.
>
> c) These two files were then used as input for STELLA calculations. The
> STELLA calculation started nicely but seems that it fails to converge. On a
> 16GB RAM and octa-core processor machine, the calculations ran up to a
> period of more than 24hours but the light curve only up to 7days was
> produced with the calculation still going on.
>
> Please suggest me some possible methods to get convergence of STELLA
> calculation. Also, suggest if I am doing something wrong.
>
> With thanks and best regards,
> Amar
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
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