[Mesa-users] Opacity tables for new and different mixtures.

[Marc Pinsonneault]

Hello all.  I’d like to talk about opacity tables.

Large stellar surveys have really transformed our ideas about how abundance
patterns change in stars;

there has also been interesting new work on the base solar mixture.



In the former case, at minimum we now know that abundances in stars are (at
least) a 2-dimensional family, usually given as [Fe/H] and {alpha/Fe].

For example, see Weinberg et al. 2022,



https://ui.adsabs.harvard.edu/abs/2022ApJS..260...32W/abstract



The default mesa cases assume solar [alpha/Fe], and include two “older”
solar mixtures – Asplund 2009 and Grevesse+Sauval 1998.

There are two recently published solar mixtures.  The “low metallicity”
solution, which builds on Asplund 2021, is Amarsi et al. 2021



https://ui.adsabs.harvard.edu/abs/2021A%26A...656A.113A/abstract



The “high metallicity” solution, also 3D NLTE, is Magg et al. 2022,



https://www.aanda.org/articles/aa/pdf/2022/05/aa42971-21.pdf



Note that the latter is fully consistent with helioseismology, and in my
view it should be the default recommended base mixture.


For full self-consistency, one should use high temperature opacities, low
temperature (molecular) opacities, and model atmospheres with the
appropriate mixtures.

There are public websites that can be used to generate custom opacities –
for example, here is the web interface for the opacity project.

https://opserver.obspm.fr/rmos.shtml

and here is the one for the Marigo low temperature opacities

http://stev.oapd.inaf.it/cgi-bin/aesopus

However, in practice these do not immediately make tables in formats
suitable for stellar interiors calculations. The standard interiors opacity
tables for MESA (and other evolution codes) use 126 different x / y/ z
combinations, for example, and online resources are one at a time. This
makes quick calculation of new tables challenging.

Given this, I’m reaching out to the atomic physicists to see if we can get
a more general set of opacity tables for community usage, and this would
include updating the MESA documentation to indicate a more general set of
options / resources. One place where I am stymied, however, and the reason
for this email, is whether this is “already done” in part – e.g. are there
already general tables available for, say, alpha to iron enhancement that
we could point to? Or is this something that we need to make available as a
community resource?



Cheers



Marc Pinsonneault
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