[mesa-users] restarting mesa binary and donor/accretor switching

[Pablo Marchant]

Hi Sterl. MESAbinary effectively assumes the photos are synchronized, and
actually overrides the photostep control of the stars so they have the same
value. I have seen this behaviour when starting with saved models that dont
have matching model numbers. This can be sorted out by fixing the initial
model numbers at the beginning of the run. I guess something of this sort
has to be your issue, as the model numbers are different at the end of your
run.

Right now I'm only with my smartphone so its a bit complicated to actually
check your files. in ~2 weeks I could give them a good look. In the
meantime you could just rename the photos to have the same number, and
restart using that number.

I think the donor switching was only setted up to work with the roche_lobe
scheme for mass transfer (you can check it on the subroutine set_donor_star
in binary_evolve, just ignore the stuff about "contact" which is something
experimental I have in there). I did not experiment to much with these
options, so right now I cant remember the reason for that limitation. But
we can certainly adjust it for your needs.

Cheers!
Am 17.09.2015 6:50 nachm. schrieb "Sterl Phinney" <esp at tapir.caltech.edu>:

> Dear Pablo, Bill et al,
>         Following on from my MESA summer school lectures, I have
> been experimenting with further with MESA binary and evolve_both_stars =
> .true.
>         I am using mesa-7624 (current release). The inlists and input
> saved models in the attached Algol.zip file sort-of succesfully make Algol
> (the final exercise of my Lecture 2).  But I decided to run the evolution
> further, and have encountered two mysteries.
>
> 1. The model numbers in photos1/ and photos2/ are not synchronized,
> while restarts seem to assume that they are, and thus don't work properly.
> Details of mystery 1:
>  During a run, log output and timestamps confirm that
> photos1/x750
> photos2/x700
> are a pair associated with a single evolutionary time,
> and the run terminates also writing unequal photo numbers for star
> 1 and star 2:
> ---
> save LOGS1/profile20.data for model 1790
> save photos1/x790 for model 1790
> save LOGS2/profile23.data for model 1743
> save photos2/x743 for model 1743
> termination code: Terminate because accretor (r-rl)/rl >
> accretor_overflow_terminate
> ---
>
> But when I restart, there are weird jumps in the star mass suggesting
> that non-matched photos are being used to restart star 1 and star 2.
> Looking into run_binary_support.f90
> I see lines
>        doing_restart = (ierr == 0)
>        if (doing_restart) then
>            read(iounit,'(a)', iostat=ierr) photo_filename ! same for both
> stars
>
> which suggests to me that MESA is in fact assuming the right thing to do
> is to use the same photo for both stars, and I don't see a way to input
> the correct, non-matching photonumbers for the two stars.  What am I
> missing here?
>
> 2. When MESA terminates the evolution of Algol (see final log output in
> mystery 1 above: "Terminate because accretor (r-rl)/rl >
> accretor_overflow_terminate"), star 1 (the first donor, and initially more
> massive star) has become a hot white dwarf, accretion has long ago ceased,
> and star 2 has just filled its Roche lobe for the first time and ought to
> become the new donor to star 1.
>
> In my inlist, I set
> keep_donor_fixed = .false.
> which I'd thought would allow the former accretor (star 2) to be
> relabelled as the donor, and permit evolution to continue with
> accretion from star 2 onto star 1.
> But since the termination code is stopping with
> "Terminate because accretor (r-rl)/rl > accretor_overflow_terminate"
> clearly that relabelling isn't happening.
>
> I see that I could also set "accretor_overflow_terminate" = [something >0]
> which might allow evolution to continue, but this isn't a case
> of both stars filling their Roche lobes, but of a desired switch of
> accretor to a donor. How do I make that happen?
> (I'd experiment more myself if I didn't have to run for an hour
> to get to this stage: see mystery 1!).
>
> Thanks, Sterl
>
> --
> E. Sterl Phinney
> Professor of Theoretical Astrophysics &
> Executive Officer for Astronomy and Astrophysics
> California Institute of Technology, 350-17
> Pasadena CA 91125 USA
>
> [on sabbatical until 18 March 2016 as
>  Radboud Excellence Initiative Professor
>  Department of Astrophysics
>  Radboud University
>  P.O. Box 9010,
>  6500 GL Nijmegen, The Netherlands]
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