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

[Bill Paxton]

Hi Tassos,

As of 7607, there is a "other_before_struct_burn_mix" in addition to the existing "other_after_struct_burn_mix".
The "before" call happens after we have done remeshing (and any mass change and any element diffusion).
It is immediately followed by the "struct_burn_mix" call that invokes the newton solver to change the structure for the evolution during the step.
The "after" call immediately following the successful completion of the newton iterations.
Hope that does the trick for you.

Cheers,
Bill



On May 27, 2015, at 7:09 AM, Anastasios Fragkos wrote:

> 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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