[mesa-users] ionization fraction or kap table ?

[Matthew Clayton]

Hi all,

To add to Rich's answer, you can get MESA to output
neutral_fraction_H
neutral_fraction_He
and
avg_charge_He
to profiles. Different linear combinations of these 3 values will give you all of the ionization fractions of H and He (exercise for reader).

If you're looking to do calculations using ionization fractions within MESA itself, you can use the ionization module. Call eval_ionization() from ionization_lib and you can get lots of ionization data on a per-cell basis (I believe this is where the data in the profile output I mentioned above actually comes from). Word of warning though: that routine does occasionally give negative ionization fractions (or at least it did last time I used it), so I'm not sure how accurate it is in all cases.

Hope that helps.

Cheers,

Matthew

________________________________
From: Jing Luan [jingluan.xw at gmail.com]
Sent: 27 June 2017 16:01
To: RICHARD H D TOWNSEND
Cc: mesa-users at lists.sourceforge.net users
Subject: Re: [mesa-users] ionization fraction or kap table ?

Thank you very much, Rich. It is very useful :-) :-)

Sincerely,
Jing

On Mon, Jun 26, 2017 at 9:27 PM, RICHARD H D TOWNSEND <townsend at astro.wisc.edu<mailto:townsend at astro.wisc.edu>> wrote:
Hi Jing —

> On Jun 24, 2017, at 9:55 AM, Jing Luan <jingluan.xw at gmail.com<mailto:jingluan.xw at gmail.com>> wrote:
>
> Dear mesa users,
>
> 1, Are there parameters in mesa that tells the ionization fraction of (HI to HII) and of (HeI to HeII) please? I search around mesa/star/public/star_data.inc, but did not find any. But maybe I miss something there.
>

I would suspect not. Nowadays, with tabulated EOS’s, it is unusual to actually solve the Saha equation during a stellar evolution calculation. However, MESA *can* tell you the free electron number density, and so you could calculate the ionization fractions yourself, using the Saha equation (for this, I suggest you ignore excited states of the H/He).

> 2, For calculating kappa mechanism due to H or He opacity bumps for driving stellar oscillation, which kappa table and eos table should be adopted please? The default in mesa-r8118 are
>
> kappa_file_prefix = 'gn93'
>
> eos_file_prefix = 'mesa'
> eosDT_Z1_suffix = '_CO_1'
> eosPT_Z1_suffix = ‘_
> CO_1'
>

For the blue edges of the classical (Cepheid) instability strip, plotted in Fig. 14 of Paxton et al (2015), I used:

initial_zfracs = 6 ! Asplund et al. (2009)
kappa_file_prefix = 'a09' ! Asplund et al. (2009)

…in the &star_job namelist, and

initial_Y = 0.2703 ! Asplund et al. (2009) / proto-solar
initial_Z = 0.0142 ! Asplund et al. (2009) / proto-solar

…in the &controls namelist. I expect the metallicity is less important to driving classical Cepheid pulsations than the relative H/He abundances.

cheers,

Rich

> Many thanks 😊😊😊😊
>
> Sincerely,
> Jing
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