<p>Welcome to the world of software developed by scientists for their own use.
There are not many clues.</p>
<p>The top-level README cites <a href="https://ui.adsabs.harvard.edu/abs/2016A%26A...594A..55N/abstract" rel="noreferrer">Nemravová et al. 2016</a>.
That paper mentions PYTERPOL briefly in section 3.4 and says &quot;solar metallicity was assumed&quot; for the components of <em>ξ</em> Tauri.</p>
<p><a href="https://github.com/chrysante87/pyterpol/blob/master/fitting/parameter.py" rel="noreferrer">pyterpol/fitting/parameter.py</a> has this code:</p>
<pre><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)),
)
</code></pre>
<p>I think <code>z=1.0</code> means the metallic mass fraction is the same as in the Sun, and other <code>z</code> values between 0 and 2 would be relative to that.</p>

CC BY-SA 4.0
2021-08-30T17:24:40.690Z
Thank you very much.
Anna-Kat
CC BY-SA 4.0
2021-08-30T17:03:56.090Z
2021-08-30T17:03:56.090Z
Mike G
<p>Does z stad for the mass fraction of all the remaining chemical elements except helium and hydrogen, please?</p>
<p>Source:
<a href="https://github.com/chrysante87/pyterpol/wiki" rel="nofollow noreferrer">https://github.com/chrysante87/pyterpol/wiki</a></p>
<p><a href="https://i.sstatic.net/mdNpD.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/mdNpD.png" alt="enter image description here" /></a></p>

<data-analysis>
What is z in this program?
Anna-Kat
# What is z in this program?

(Asked by: username_0 on 2021-08-30)

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

Source:
<https://github.com/chrysante87/pyterpol/wiki>

[![enter image description here](https://i.sstatic.net/mdNpD.png)](https://i.sstatic.net/mdNpD.png)

**Tags:** data-analysis


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## 1 answers

### Answer by username_1 on 2021-08-30. Score: 8 | Accepted 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](https://ui.adsabs.harvard.edu/abs/2016A%26A...594A..55N/abstract).
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](https://github.com/chrysante87/pyterpol/blob/master/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.

> **Comments:**
> **username_0**: Thank you very much.  

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