[mesa-users] recombination/ionization energy source/sink

[Anastasios Fragkos]

Thank you Bill!

I ended up using your suggestion for the “approximate” solution, which however for H and He turns out to be exact. From the already available profile output avg_charge_H and neutral_fraction_H, one can calculate exactly the number of atoms in each ionization state for H and He. For heavier elements with more ionization states this is not possible with the available information. But since I only cared for H and He this was enough for me. 

So all is good when all I want is to calculate the energy stored in ionized H and He. However, when I want to calculate the power source/sink because of recombination/ionization throughout the star, then what I currently do is to compare the energy stored in ionized H and He in two consecutive model and effectively do a numerical derivative. At this point the process starts becoming more “approximate" though, as each model has a different number of shells and I need to also do an interpolation.

I was thinking that the additional interpolation could be avoided if one could calculate the energy stored in ionized H and He at the beginning and at the end of a timestep, before MESA does the remeshing, and calculate the difference in the energy stored shell per shell. Performing some calculations at the end of a timestep can be done through the function extras_finish_step. Is there something equivalent for adding extra code at the beginning  of a step?

Thank you again,
Tassos


> On 22 May 2015, at 17:34, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> 
> Hi Tassos,
> 
> I imagine the 1st step is just to find the ionization states for each species.
> But even that is not explicitly available -- it is cooked into the opal and scvh eos results.
> 
> You can do-it-yourself with a little Saha using the available eos info.    If you create such a tool, let's add it to mesa.
> 
> Alternatively, for an approximate answer, you can call the mesa/ionization routines eval_ionization or eval_typical_charge.
> It returns average ionic charges based on
>      ! C. Paquette, C. Pelletier, G. Fontaine, G. Michaud,
>      ! "Diffusion in White Dwarfs: New Results and Comparative Study",
>      ! ApJ Supp. Series, 61:197-217, 1986.
> 
>   and ionization potentials from
>      ! Allen, C.W., 1973, "Astrophysical Quantities", 3rd edition, pg 37-38.
> 
> 
> Let us know what you come us with as a solution.
> 
> Cheers,
> Bill
> 
> 
> 
> 
> 
> 
> On May 22, 2015, at 5:34 AM, Anastasios Fragkos wrote:
> 
>> Hi all,
>> 
>> I want to examine the effect that artificial heating or cooling of the envelope of a giant star has on the ionization levels of different species. Specifically, I would like to extract from mesa the recombination energy that is released in different parts of the envelope, as ionized material gets recombined. Looking through the profile_columns.list, it doesn’t seem like such a quantity can be directly exported. I would really appreciate any help on deriving this quantity.
>> 
>> Best wishes,
>> Tassos
>> 
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