[mesa-users] Core hydrogen mass fraction increases in early evolution of 1.5 Msun star

[David Arnett]

I agree with Cony and Bill. This often happens in stellar codes when
convection begins. Whether it is physical is a different question. It
seems to be due to the use of the Schwarzschild criterion for mixing,
which ignores composition effects. At the same pressure, H is lighter
than He, so buoyancy inhibits mixing H down. Entrainment may still do
the trick, but that takes us beyond the present algorithm. We show the
composition effects in Viallet et al, 2013 (Jan. astroph).

-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona