[mesa-users] Binary capabilities on MESA

Bill Paxton paxton at kitp.ucsb.edu
Thu Oct 4 12:47:46 EDT 2012

Hi Pablo,

Good to hear from you.  As a start, if you haven't already done it, run the 4 test_suite cases for binary evolution and make plots of the evolution of binary period etc.  The tests are for the combinations of {model internal evolution of one star of binary (other is point mass), model internal evolution of both stars} and
{pick mdot explicity at start of time step based on roche lobe overflow, select mdot implicitly by repeated guesses until get radius at end of step to equal the roche lobe at the end of the step}.  Those 4 combinations are in the test rlo, rlo_implicit, binary_rlo, binary_rlo_implicit.

Look at the src/run_star_extras routine called "data_for_extra_history_columns" -- it adds a bunch of things to the history log concerning the binary.
At the end of the run, you can make plots for the evolution of things like the following (from the rlo test case).
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While your run_star_extras has the data_for_extra_history_columns routine, you'll find that the routines that are doing the actual binary modelling are elsewhere.  They are in the file star/binary_systems/rlo_routines.inc that is included as part of your run_star_extras for compilation.  Take a look.

You might recall that Tassos Fragos was also very interested in improving the binary routines in mesa, and he's an excellent FORTRAN programmer so you might want to collaborate with him on this.  Selma de Mink (sedemink at gmail.com) has also expressed interest in this, so you might check with her as well.  I think this is a project whose time has come!  Lots of good people are interested in making it happen.

Please keep me in the loop -- I'm very interested in this myself.


On Oct 4, 2012, at 5:03 AM, Pablo Marchant wrote:

> Hi! Last August at the MESA summer school we had a small session where we discussed the binary evolution capabilities of MESA. As far as I can remember, Bill Paxton said that the current implementation for binaries is more a "proof of concept" than a robust implementation (not his precise words but something on that line). In that sense, the current code has restrictions, as for instance only one star can be an accretor while the other one is set as the donor in a fixed way at the beggining of the simulation. Also, tidal torques are not implemented.
> Even though I'm not very experienced in FORTRAN, I've been skimming through the source code trying to understand where these things are done, but not to much avail. I've also been playing with the binary examples on the test suite (binary_rlo and binary_rlo_implicit, which have equal initial conditions but different implementations for mass transfer), but I have no idea if there's a simple way to output info on the binary system itself.
> So, going to the point ... I'm really interested on getting a robust implementation for binaries on MESA, so mostly I'd like to know more precisely what are the limitations of the current implementation and if it's part of the development roadmap to enhance this capability. In any case, I would not have problems on getting involved on actual development for this functionality.
> Cheers to all!
> -- 
> Pablo Marchant Campos
> M.Sc on Astrophysics, Universidad Cat?lica de Chile
> PhD student, Argelander-Institut f?r Astronomie
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