[Mesa-users] Re：On split mixing, ask for some Ref. about op_split_burn_limit_min_T

[Rob Farmer]

Hi

op_split_burn has not yet been documented in a mesa paper.

What it is, is an operator split mode for the nuclear burning and
composition change. Normally MESA would compute the composition change
(dy/dt) once per step and feed that into the jacobian. This has been
numerically challenging at high temperatures when reaction rates get very
large, adnw e have difficulty keeping things within some numerical
tolerances. So now when op_split_burn is true and the local zone
temperature is above op_split_burn_min_T we use a different method. We
break the timestep for a zone in to set of smaller sub time-steps (just for
the nuclear burning calculations), integrate over these smaller sub-steps,
and then feed that result into the global jacobian This means that each
zone can be evolved with the same global timestep, while taking as many
smaller substeps as needed (and not forcing the entire stellar model to be
evolved at the smaller timescale) to maintain numerical tolerances.

Generally I would recommend op_split_burn_min_T ~ 1d9 as there is not much
benefit at lower temperatures. But 25M_pre_ms_to_core_collapse is a
difficult test case to keep working so we probably set it at a lower
temperature to move the transition between non-split burn and split_burn
and get the model working.

Rob


On Mon, 16 May 2022 at 00:46, 姜龙 via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear mesa users,
>
>
> I am doing some simulation about the late stage of massive stars with MESA
> r-12778, inlist files following
>  star/test_suite/25M_pre_ms_to_core_collapse. I have noticed the change of
> inlist_to_lgT_9.9. In it, op_split_burn is set to true and the
> op_split_burn_min_T=1d6 is adopted. Since there is no Ref. about this topic
> in the file, I am wondering what the detail meaning of these settings.
>
>
> Could someone give me some Ref. about this topic?
>
>
> Thanks for your help in advance!
>
>
> Long, Jiang
>
>>
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