[Mesa-users] different expression of z

[李宗恒]

Thank you so much!
And is it to say zbase must equal to initial_z?
Thanks again

---- Replied Message ----
| From | Jared Goldberg (Guest Researcher)<jgoldberg at flatironinstitute.org> |
| Date | 10/07/2025 22:17 |
| To | 李宗恒 <lzh17513652589 at 163.com> |
| Cc | mesa-users<mesa-users at lists.mesastar.org> |
| Subject | Re: [Mesa-users] different expression of z |
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




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