[Mesa-users] Convergence of massive Population III stars

[Amedeo Romagnolo]

Dear Jake,

>From my experience with non-popIII very massive stars, the major problem
with reaching core-collapse in the models is that MESA usually doesn’t
manage to converge somewhere in the envelope.

Now, I cannot read your inlists at the moment, but if you hadn’t done it
yet you could try, when approaching core collapse, to increase your
resolution in the regions above 10^9 K (there are a couple of variables in
MESA you can change to make it happen) and decrease the resolution for the
envelope.

I cannot guarantee that this will work, but for a couple of simulations
this actually helped me to reach core collapse without having my HR diagram
look like a cubist painting :)

Hope that helps.

Cheers,

Amedeo

On Fri, Jan 24, 2025 at 6:09 PM Jake Hassan via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Hi everyone,
> I'm attempting to model very massive Population III stars using MESA
> r24.08.1 (SDK version 24.10.1), based on the parameters described in Yoon
> et al. 2012 (
> https://ui.adsabs.harvard.edu/abs/2012A%26A...542A.113Y/abstract). For
> now I'm focusing on nonrotating metal-free stars, and I've been able to
> evolve ones with initial masses up to 80 Msun to core collapse.
>
> For higher initial masses though (still nonrotating), my models go awry in
> the later stages. For example, at 90 Msun the evolution gets very close to
> core collapse, but suddenly becomes haywire and the timestep plummets (see
> attached images). For 100 Msun, it only goes as far as O-burning before
> halting for several hundred steps and eventually evolving erratically (also
> attached). In both cases it seems to be associated with "logT >
> hydro_mtx_max_allowed_logT" and "logRho > hydro_mtx_max_allowed_logRho"
> errors, though raising hydro_mtx_max_allowed_logT and
> hydro_mtx_max_allowed_logRho to higher values did not fix the issue.
>
> I suspect the problem is related to overshooting. I've been using the
> 20M_pre_ms_to_core_collapse test suite as a guide, and it includes a small
> amount of overshooting in Z-burning regions for numerical stability (with
> overshoot_f = 0.005). This is necessary for my inlists to converge too,
> since excluding it would cause even my 80 Msun models to diverge in the
> same manner I described for the 90 Msun models. I haven't found a value of
> overshoot_f that yields convergence at higher masses, but 0.017 seems to
> work the best for the 100 Msun model, allowing it to get as far as Si
> burning before going haywire (higher or lower values than 0.017 won't get
> past O-burning). However, 0.017 prevents the 90 Msun model from reaching as
> far as 0.005 would.
>
> I would appreciate any advice on this. I've attached two inlists:
> inlist_to_end_core_he_burn evolves the star from pre-MS to the end of He
> burning, while inlist_to_cc evolves it from that point to core collapse.
> The only differences between these files are the termination conditions and
> whether we load a saved model. Let me know if anything else would be
> helpful.
>
> Thanks,
> Jake
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>
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