[mesa-users] Question about abundances in the 1 Msun test problem

Bill Paxton paxton at kitp.ucsb.edu
Thu Aug 7 12:11:10 EDT 2014

On Aug 7, 2014, at 4:39 AM, Manos Chatzopoulos wrote:

> I just experimented with the set_uniform_xa_from_file option and I am a happy customer too,


> though for the inexperienced MESA user some relevant "flags" in the inlist that allows the control of the
> abundances might be a more straightforward option.

it is possible to do it all from the inlist too.   There are 2 test cases as examples:
make_massive_with_uniform_composition and make_low_mass_with_uniform_composition

in &star_job, add these lines

      relax_initial_to_xaccrete = .true.
      num_steps_to_relax_composition = 50

in &controls, set the abundances in xaccrete.
in the test cases we just set a C/O mixture, but you
can specify as many isotopes as there are in your net.

         ! C/O MIX
         ! set target uniform composition for relax_initial_to_xaccrete
         num_accretion_species = 2
         accretion_species_id(1) = 'c12'
         accretion_species_xa(1) = 0.2145d0
         accretion_species_id(2) = 'o16'
         accretion_species_xa(2) = 0.7855d0


>> i’m not one to generate unnecessary work or endless options.
>> personally, i use set_uniform_xa_from_file when i want to set
>> an exact composition. let’s try an mini-experiment on sensing
>> what the community thinks would be useful.
>> mesa-users:
>> is the current two completely general schemes and the proposed options
>> for choosing between "dump missing metals in the most massive isotope”
>> and "renormalize the metals” sufficient for your immediate purposes or
>> is additional flexibility needed? no response means you are ok with the
>> current adjustability.
>> fxt
>> On Aug 6, 2014, at 8:00 PM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>>> On Aug 6, 2014, at 7:42 PM, Francis Timmes wrote:
>>>> how about a third option, “dump into the most abundant isotope”?
>>>> for this particular case, a touch more h1 may be the least perturbing solution.
>>> Hi Frank,
>>> yes, i know i did something other than what you recommended. ;D
>>> the reason is that it was easy to do what i did, and it is a bit harder to do
>>> what you suggested given the current way the code is structured.
>>> it currently gets the X and Y info from the user and then picks
>>> a set of metal mass fractions from a given set to provide the
>>> remaining Z.  So transferring from Z to X or Y isn't currently
>>> an easy to implement option whereas changing the choice
>>> of metals is.    so i did the easy one first.
>>> i can see it now --- after adding a 3rd option to add to the most
>>> abundant, we'll need a 4th option that lets the user specify
>>> which element to use for the extra, and then 5th that says
>>> split the extra between H1 and He4, and then a 6th that
>>> says distribute the extra over all the isotopes, and then ....
>>> everyone should keep in mind that we already have 2
>>> completely general ways to see any uniform composition
>>> by giving the set of desired mass fractions.    one is
>>> set_uniform_xa_from_file and the other is set_to_xa_for_accretion.
>>> so at some point we'll stop adding options and just say
>>> "use one of the general schemes".    but if you think it is
>>> important to add “dump into the most abundant isotope”
>>> then i'll take another look at how to do it.   you say.
>>> -Bill
> -- 
> Dr. Manos Chatzopoulos
> Enrico Fermi Postdoctoral Fellow
> Department of Astronomy & Astrophysics
> FLASH Center for Computational Science
> University of Chicago

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