[Mesa-users] Ni56 getting converted to Fe isotopes during SN shock breakout

[Jared Goldberg (Guest Researcher)]

The Ni56 is reset in inlist_shock_part5 to a user-specified value via a set
of x_ctrls which are called during the set_nico_mass routine in
run_star_extras.f90.

Specifically the lines:
  x_ctrl(12) = 1d-15 ! amount of ni56 to add << This is in Msun
  x_ctrl(35) = -1d+99 ! put ni56 this + m_center
  x_ctrl(36) = -1d+99 ! end ni56 at this + he_core_mass

In short, you're telling it to remove all the nickel. Set x_ctrl(12) to -1
to ignore the switch, or set it to your value of choice (I think ~ 0.03 -
0.07 are typical for partially-stripped IIP's).

In general, overwriting abundances is sometimes but not always the issue in
STELLA.

Best,
~Jared

On Wed, Apr 8, 2026 at 11:49 AM Mandal, Soham (uqa7ur) via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear MESA users,
>
> I have been trying to model core collapse and eventual shock breakout in a
> massive star, using the 'ccsn_IIp' problem in star/test_suite as a
> template. The pre core-collapse star is a partially stripped massive star
> of solar metallicity, with M_ZAMS = 16Msun, and M_env (at core collapse) =
> 1.27Msun. The eventual goal is to handoff these models to STELLA and
> produce lightcurves.
>
> STELLA crashes early and produces erroneous lightcurves. Upon
> investigating the shock breakout phase and looking for sharp abundance
> changes in the profiles, I find that Ni56 abundances in the model profiles
> suddenly drop dramatically between inlist_shock_part4 and
> inlist_shock_part5. This is accompanied by sudden increase in Fe52 and Fe54
> abundances. The temperature profile remains around log T[K] ~ 5.5, which
> rules out nuclear burning. I do not understand (i) why all the Ni56 is
> getting converted into Fe isotopes, and (ii) if this is related to
> numerical issues encountered by STELLA.
>
> I'd greatly appreciate if someone is aware of/encountered similar issues
> with shock breakout in MESA and could chime in! The inlists and a snapshot
> of the profile abundances for shock_part4 and shock_part5 are attached to
> the email. Thanks for your attention! Please let me know if more
> information is required.
>
> Best,
> Dr. Soham Mandal
> VITA postdoctoral research fellow
> Department of Astronomy
> University of Virginia
> _______________________________________________
> mesa-users at lists.mesastar.org
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