[mesa-users] relax_initial_composition

Tue Apr 29 11:23:20 EDT 2014

Hi everyone,

I’ve looked over the archives for information on using the relax_initial_composition feature, but I haven’t been able to find anything helpful, so I thought I would send out a general post. 

Basically, I’m trying to get one of my white dwarf models to relax to a given (very simple) chemical profile so that I can compare with the results of Salaris, Althaus, and Garcia-Berro (http://adsabs.harvard.edu/abs/2013A%26A...555A..96S). 

Has anyone had success converging a MESA input model to have a new, externally-specified chemical profile? I have only been able to get the feature to partially work.

From star_job.defaults, we have

! relax composition
     relax_initial_composition = .false.
     num_steps_to_relax_composition = 100 ! use this many steps to do conversion
     relax_composition_filename = '' ! file holding composition profile information
        ! file format for relax composition
        ! 1st line: num_species  num_points
        ! then 1 line for for each point where define desired composition
        ! xq xa(1) ... xa(num_species)
           ! xq = fraction of xmstar exterior to the point
           ! where xmstar = mstar - M_center
           ! xa(i) = mass fraction of i'th species
        ! NOTE: it is up to you to ensure that the current net isotopes match
        ! the species in the composition file.
        ! you can set show_net_species_info = .true. to check the isotopes in the net.

The first line is supposed to be 

num_species  num_points

but I find I have to reverse these, i.e., num_points num_species. I’m basing this on the following write statement I put on line 342 of relax.f:

write(*,*) 'species check: ',species, s% species

which told me that the number of species was in the hundreds. By switching them around I get past this check. 

If I set eps_nuc_factor = 0.0 then I’m able to get it to run and “converge” to a profile. In case anyone else would like to try this, here are the inlist + other files that I used:

So, this does run and produce results. When it finally displays the composition, however, I see that my white dwarf has been transformed into a pure hydrogen star! It’s no wonder that this wouldn’t converge unless nuclear reactions are turned off. 

Naturally I suspect that I’m not using the correct file format for the composition profile. Here’s what I currently have:

 234 8
1.000000000000 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
0.999995394800 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
0.999988487100 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
etc.

So, I have 8 species, and the composition is defined in 234 shells, from the center to the surface. Labeling the columns, I have

  1. - M(r)/Mstar         h1                 he3              he4               c12             n14             o16              ne20           mg24
1.000000000000 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
0.999995394800 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
0.999988487100 0.00000000 0.00000000 0.00000000 0.50000000 0.00000000 0.50000000 0.00000000 0.00000000
etc.

So, Mesa is acting as if the h1 column has 1.000 everywhere and the other columns have zeros everywhere. 

Does anything leap out at anybody about what I might be doing wrong?

Thanks!

Mike

_____________________________________

Michael Houston Montgomery
Department of Astronomy
University of Texas
email:  mikemon at astro.as.utexas.edu
www.as.utexas.edu/~mikemon/
_____________________________________

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