[Mesa-users] crashes at Psurf=1 Ba

[Sho Shibata]

Hi all,

I'm running test simulations where I smoothly change the surface pressure
while keeping the surface temperature fixed, using
atm_option='fixed_Tsurf_and_Psurf'. I'm using MESA Version: mesa-24.08.1,
and I use run_star_extras.f90 to implement the smooth change of Psurf, but
no other modification.

I am encountering unexpected crashes: MESA can evolve with a varying
surface pressure, but the code consistently crashes exactly when the model
attempts to cross P_surf = 1 bar. The attached figures show what I’m doing.
Changing the fixed temperature does not shift the crash location—the
failure always occurs at P_surf = 1 bar.

I see a similar issue when varying T_surf with fixed P_surf, specifically
when crossing T_surf = 1000 K.

Initially, I suspected the EOS tables, so I reran the experiment using the
ideal EOS (by turning off other EOS tables), but the crash still occurs.

Do you have any idea what might be happening internally in MESA in this
situation? And is there a way to resolve or work around this issue?

For context, these tests involve a planetary-sized object—an atmosphere on
a Moon-sized protoplanet—so the envelope is extremely thin. The imposed
change is rapid, but the timescale itself should not be the root of the
problem.

Any advice or suggestions would be greatly appreciated. Thanks in advance
for your help.

Best regards,
Sho Shibata
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