[mesa-users] Problem evolving a donor star

[Pablo Marchant]

Odette, effectively the problem is the timestep. The loaded model starts
with a huge timestep (about a third of a Gyr), and using that timestep in a
close system with magnetic braking results in a negative total angular
momentum. To make your system run, force a smaller initial timestep by
adding this to your star_job section of inlist1:

      set_initial_dt = .true.
      years_for_initial_dt = 1

Also, maybe you want to create your initial models with a better time
resolution. Might not be neccesary (maybe the model has achieved proper
convergence already), but I'd recommend you to use a smaller
varcontrol_target there.

Cheers!

On Wed, Dec 10, 2014 at 6:40 PM, Odette Toloza <odette.toloza at gmail.com>
wrote:

> Hola Pablo,
>
> Thanks for helping me.
>
> I've installed the latest version, 7184. Maybe having a look into the time
> step could handle it, I mean constraining the maximun value. I do not know.
>
> Find attached the files.
>
>
> Cheers,
> Odette.
>
>
> 2014-12-10 17:11 GMT+00:00 Pablo Marchant <pamarca at gmail.com>:
>
>> Hola Odette!
>>
>> Usually that error message appears when angular momentum comes out
>> negative. That can happen since we compute delta J = jdot*dt (just the
>> Euler method). However it usually means something else is wrong. Could you
>> provide me with your full set of inlists and saved models (together with
>> your MESA version) to check wether this is a bug?
>>
>> Cheers!
>>
>> On Wed, Dec 10, 2014 at 5:47 PM, Odette Toloza <odette.toloza at gmail.com>
>> wrote:
>>
>>> Hi Mesa-users
>>>
>>> I am relatively new with MESA, and I am having troubles with evolving a
>>> binary system containing a evolved donor. Based on the
>>> binary_donor_only_implicit_mdot suite test we have tried to evolve white
>>> dwarf of 0.8 solar masses together with a donor star of 1 solar mass. But
>>> first at all we created a model for the donor starting from the ZAMS and
>>> stopping the evolution controlling the core composition.
>>>
>>>
>>> xa_central_lower_limit_species(1) = 'h1'
>>> xa_central_lower_limit(1) = 0.5  ! or less evolved 0.8
>>>
>>>
>>> When we include this model on the binary_donor_only_implicit_mdot suite
>>> test and we make sure that with an orbital period of 0.6d the system is out
>>> of contact. It starts running but as soon as the mass transfer starts MESA
>>> stops. The first amount of mass transferred is too high and MESA collapses
>>> returning negatives values for angular momentum (STOP bad
>>> angular_momentum_j).
>>>
>>> the orbit shrinks quite fast since the jump of (r-rl)/rl is too abrupt
>>> before the last step is 6.421261633E-01 and in the last step is
>>> -1.409570580E-02, as well as lg_mdot, from -2.062847169E+01 to
>>> -9.900000000E+01
>>>
>>> We have considered all the mechanisms of jdot,
>>>
>>>    do_jdot_gr = .true.
>>>    do_jdot_ml = .true.
>>>    do_jdot_ls = .true.
>>>    do_jdot_missing_wind = .true.
>>>    do_jdot_mb = .true.
>>>
>>>
>>>
>>> For some reason MESA complains with the inclusion of an evolved donor.
>>> To make sure that we are not making any mistake during the inclusion of the
>>> model, we created another evolved model this time with 80% of hydrogen in
>>> the core. When we include it, MESA runs without problems.
>>>
>>>
>>> Does anyone have any idea why this could be happen?
>>>
>>> Cheers,
>>> Odette Toloza
>>>
>>>
>>>
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>>
>>
>> --
>> Pablo Marchant Campos
>> M.Sc on Astrophysics, Universidad Católica de Chile
>> PhD student, Argelander-Institut für Astronomie
>>
>
>


-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD student, Argelander-Institut für Astronomie
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