[Mesa-users] crashes at Psurf=1 Ba

[Farag, Ebraheem]

Can you add "report_ierr = .true.", and check if something gets spit out at the moment the model begins to timestep dive, rather than the last timestep? The last timestep is rarely informative.

-EbF
________________________________
From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of Sho Shibata via Mesa-users <mesa-users at lists.mesastar.org>
Sent: Friday, November 21, 2025 8:50 PM
To: Philip Mocz <pmocz at flatironinstitute.org>
Cc: Jeremy Sakstein via Mesa-users <mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] crashes at Psurf=1 Ba

Hi Philip,

I wrote Psurf = 1 bar in the email, but that was a typo. The crashes occur at Psurf = 1 Ba. The figure is correct. Sorry for the confusion.

Yes, the timestep is becoming really small and in most cases MESA stops because of the too small timestep.
The bellow is one of the error message.

----------------
                                         solver rejected trial model
                                        s% model_number         135
                                  s% solver_call_number         169
                                                     nz         354
                                         s% num_retries          34
                                                     dt    1.4937230988914816D+07
                                          log dt/secyer   -3.2483387012067205D-01

 retry: max residual jumped -- give up in solver     135
       retry log10(dt/yr), log10(dt), retry_factor     1   135       -0.926894        6.572210        0.500000
                      residual_norm > tol_residual_norm         135    9.4041696866144896D-03    1.0000000000000000D-08
                        max_residual > tol_max_residual         135    4.8329438443848197D+01    1.0000000000000001D-05
            correction_norm > tol_correction_norm*coeff         135    2.1671809254193686D-04    3.0000000000000004D-07    1.0000000000000000D-02
          max_abs_correction > tol_max_correction*coeff         135    2.9765389377772104D-03    3.0000000000000001D-05    1.0000000000000000D-02


..... repeat this messages .....


stopping because of problems dt < min_timestep_limit
terminated evolution: cannot find acceptable model
termination code: min_timestep_limit
----------------

Best,
Sho

2025年11月21日(金) 18:59 Philip Mocz <pmocz at flatironinstitute.org<mailto:pmocz at flatironinstitute.org>>:
Hi Sho,

It does look like something odd is going on right at 1 Ba

Can you share what error messages you get when you crash? Is timestep becoming really small?

Best,
Philip

On Fri, Nov 21, 2025, 7:54 PM Sho Shibata via Mesa-users <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>> wrote:

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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