# What is z in this program?

Does z stad for the mass fraction of all the remaining chemical elements except helium and hydrogen, please? Welcome to the world of software developed by scientists for their own use. There are not many clues.

The top-level README cites Nemravová et al. 2016. That paper mentions PYTERPOL briefly in section 3.4 and says "solar metallicity was assumed" for the components of ξ Tauri.

pyterpol/fitting/parameter.py has this code:

parameter_definitions=dict(
teff=dict(name='teff', value=10000., vmin=6000., vmax=50000., unit='K', fitted=False, group=0, typedef=(float)),
logg=dict(name='logg', value=3.5, vmin=0.0, vmax=5.0, unit='log(g.cm^-2)', fitted=False, group=0, typedef=(float)),
vrot=dict(name='vrot', value=0.0, vmin=0.0, vmax=500., unit='km.s^-1', fitted=False, group=0, typedef=(float)),
rv=dict(name='rv', value=0.0, vmin=-1000., vmax=1000., unit='km.s^-1', fitted=False, group=0, typedef=(float)),
lr=dict(name='lr', value=1.0, vmin=0.0, vmax=1.0, unit='relative', fitted=False, group=0, typedef=(float)),
z=dict(name='z', value=1.0, vmin=0.0, vmax=2.0, unit='Z_solar', fitted=False, group=0, typedef=(float)),
)


I think z=1.0 means the metallic mass fraction is the same as in the Sun, and other z values between 0 and 2 would be relative to that.

• Thank you very much. Aug 30 at 17:24