# What is z in this program?

Does z stad for the mass fraction of all the remaining chemical elements except helium and hydrogen, please?

## 1 Answer

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