[Mesa-users] Understanding why 'retry: get_T_tau -- L <= 0' occurs and ways of stopping it terminating my simulations

[Arman Aryaeipour]

Dear MESA-users,

I'm using MESA revision 21.12.1 to model classical novae outbursts with ejection velocity mass loss. To do this, I use the other_adjust_mdot hook to eject mass from the model as the envelope expands and the outer material exceeds its local escape velocity. However, before any significant mass is lost from the model (~2% of the envelopes mass) I encounter the 'retry: get_T_tau -- L <= 0' error. Every retry that is attempted due to this error gets the same subsequent 'retry: get_T_tau -- L <= 0' error, entering the simulation into a cycle of retries that eventually stop the simulation with the 'terminated evolution: hydro_failed' code.

If I turn off mass loss a few timesteps before I get this error, then the envelope continues in its expansion with no problems. If I limit the timestep size so as to limit the amount of mass lost per timestep during the mass loss phase, I still eventually run into the same error and simulation termination. Therefore, it appears that the mass loss is causing the 'retry: get_T_tau -- L <= 0' error.

In an attempt to stop this error, I changed the luminosity values of the surface cells to be positive values extrapolated from the interior when they are assigned to the s% L luminosity pointer in the solver_support.f90 routine, but this only made a host of other convergence issues stop the simulation instead. I have also fiddled with various MESA parameters in an attempt to stop this error too, but none have made a difference.

I'm confused as to why I suddenly get this error, and what is causing it. Can anyone kindly explain why this error can suddenly become such a big issue, and the best ways of dealing with it?

I have attached an example of the inlist I use. I would be very grateful for any help or suggestions and thank you in advance!

Kindest regards,
Arman
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