Re: [mesa-users] Z=0.04 and MESA r9793

[Josiah S. <jws...@uc...>]

Hi Philip,

> I want to use MESA r9793 to evolve a 1.3Msol, Y=0.32, Z=0.04 star from the
> zero age main sequence. I find strange behaviour near the base of the giant
> branch for this high metallicity star: a jump in L and Teff, as shown in
> the attached HR diagram (z0.04...pdf, red track, jump between the crosses).
> The same model evolved with r8845 (black track) does not show this jump.
>
> I assume this is related to changes to the opacity and/or equation of
> state, but I haven't been able to solve it. Do you have any ideas?

As you suspected, this an EOS issue.  There are OPAL tables for Z = 0,
0.02, and 0.04.  For higher Z, we switch to HELM.

The new release has controls that expose some of the blending options to
the user (as opposed to hardcoding them).

Try running with the options in star_job

    set_HELM_OPAL_Zs = .true.
    Z_all_OPAL = 1.0
    Z_all_HELM = 1.0

that should keep you on the OPAL tables (i.e. you'll never blend into
HELM).

What I don't understand (and will have to investigate) is why this
particular case behaves so badly.  There was not supposed to have been a
significant change in the default behavior.

Josiah