[Mesa-users] Setting subsolar/supersolar metallicity

[Amar Aryan]

Dear MESA users,

I am trying to evolve a subsolar (Z = Z_solar / 2 ) metallicity, 20 M_sun
ZAMS star, up to the stage of the onset of core collapse by utilizing the
"20M_pre_ms_to_core_collapse" directory in the latest MESA release,
mesa-r24.03.1. By default, the directory is set for the solar metallicity
with the following controls in "inlist_mass_Z_wind_rotation":

&star_job
   new_Z = 1.42d-2
   new_omega_div_omega_crit = 0d0
   initial_zfracs = 6 ! set to asplund 2009 abundance fractions
/ ! end of star_job namelist

&kap
   Zbase = 1.42d-2
/ ! end of kap namelist

&controls
   initial_mass = 20
   initial_z = 1.42d-2 ! ! solar
   initial_y = 0.2703d0 ! from asplund et al. 2009, solar.
   Dutch_scaling_factor = 0d0
/ ! end of controls namelist

If I set the initial metallicity to Z = Z_solar /  2, i.e., new_Z =
0.71d-2,  Zbase = 0.71d-2, and initial_z = 0.71d-2, how should I modify the
corresponding "initial_zfracs" and "initial_y"?

I noticed that there were no explicit options of "initial_zfracs" and
"initial_y" in "inlist_mass_Z_wind_rotation" in earlier versions of MESA
(e.g., in mesa-r23.05.1).  How is "intial_zfracs" different
than "initial_z"? Please suggest.

With regards,
Amar
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