[Mesa-users] Producing a medium to high mass pure Helium star

[Josiah Schwab]

Hi Charlie,


> The evolved state of this model is likely to explain the small timesteps.
>

Building on Aaron's point and your plot, you can see that this model has a
near- (or even maybe even super-) Eddington luminosity (b/c of the He shell
burning on a massive degenerate core).  Correspondingly, it has developed
an inflated envelope with outer layers that are radiation pressure
dominated and have a density inversion.  The steep entropy gradient at the
base of this (inefficient) convection zone is usually what is responsible
for driving the MESA timestep down.

This is similar to the behavior in massive stars that the MLT++ "hack"
described in Section 7 of Paxton et al. (2013) is designed to numerically
circumvent (but not physically solve).  You could consider
using okay_to_reduce_gradT_excess and related controls, depending on what
your goals for the model are.

You may also find it numerically helpful to include some mass loss in these
models.  While one may be hard pressed to make a precise physical
prediction of the mass loss rate, I don't think it is much of a stretch to
imagine driving a wind in this circumstance.

Josiah
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