[Mesa-users] different expression of z

[Jared Goldberg (Guest Researcher)]

Hi Izh,

initial_z (
https://docs.mesastar.org/en/latest/reference/controls.html#initial-z) =
the starting metallicity of the star
new_z (https://docs.mesastar.org/en/latest/reference/star_job.html#new-z) =
if you're changing/relaxing the metallicity of the star, what you're
changing it to
zbase (https://docs.mesastar.org/en/latest/reference/kap.html#zbase) = the
metallicity assumed at birth for *the opacity. *This matters because the
metal content assumed for the opacities will be different for example, for
a star that's solar-metallicity at birth and then experiences dredge-up of
C, N, O elements versus a star that is born at 0.01 x solar-metallicity,
even if both have similar "metallicity" from dredge-up since heavy element
composition will be different.

I linked the documentation so you can explore in more detail -- they are in
different inlist sections. In the future the docs should be the first place
to go to sort these kinds of questions out.

Cheers,
~Jared

On Tue, Oct 7, 2025 at 10:06 AM 李宗恒 via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear mesausers
> I have come across three different ways to represent metallicity:
> initial_z, new_z, and zbase. I also noticed that when the values of new_z
> and zbase are different, the results (such as the Hertzsprung–Russell
> diagram) differ from those when their values are the same. Could you please
> explain the distinctions between these three representations of metallicity?
> Thanks for your time
> lzh
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
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