[mesa-users] resending - Questions about physical model and numericalimplementation of binary star evolution

[Pablo Marchant]

Right now there is no built-in solution to create mergers in the binary
module, or evolve contact systems, so there is a termination condition when
the accretor overflows its Roche lobe. This can be relaxed using the
accretor_overflow_terminate_option, but you have to ask yourself whether
your results would make any sense then.

Given the amount of assumptions you would need to create a merged object, I
think it's better for the user to define how he would do that. There are
plenty of options in MESA to go in this direction.

On Thu, Dec 11, 2014 at 4:34 PM, Dean Townsley <Dean.M.Townsley at ua.edu>
wrote:

>
> (cc'ing to the list for others' benefit)
>
> I'm glad what I said was useful.  I am unsure what the mesa binary module
> does once both stars touch their Roche lobes.  From your inlist, it appears
> that is a stopping condition, I don't know what might happen after that if
> it doesn't stop.  My understanding is that the MESA binary module is
> intended for mass transfer simulations, not an actual merger that might
> take place if one star engulfs the other or if one star is disrupted, since
> in those cases the assumptions used in the MESA star module to evolve the
> distinct stars aren't really appropriate.  But I'm not an authority on the
> binary module, and I have simply avoided cases when the accretor might fill
> its roche lobe also.
>
> Dean
>
>
> On 12/10/2014 08:14 PM, 이현택 wrote:
>
>  Thank you so much to your opinion.
>
> Now I understand the physical meaning of the simulation.
>
> Yes, your guess is correct. Simulation ends with primary star's depletion
> of helium in the core.
>
> I'm still curious whether MESA can simulate the binary merger case.
>
>
>  I appreciate your advice. It is really helpful :D
>
>
>  -Cheers, HYUN TAEK
>
> ------------ 원본 메일 내용 ------------
> *보낸 사람 :* "Dean Townsley"<Dean.M.Townsley at ua.edu> <Dean.M.Townsley at ua.edu>
> *받는 사람 :* "이현택" <diolet at unist.ac.kr> <diolet at unist.ac.kr>,
> mesa-users at lists.sourceforge.net
> *메일 제목 :* Re: [mesa-users] resending - Questions about physical model and
> numericalimplementation of binary star evolution
> *보낸 날짜 :* 2014/12/10 18:42
>
> Hello,
>
> From the plots in your first email, this looks like the expected behavior
> for a secondary star losing matter via mass transfer to a primary.  When
> the donor loses enough mass to get down from 0.8 to about 0.2 Msun, it
> becomes fully convective, at which point the abundances are constant since
> the star is fully mixed.  Also since the star is steadily becoming less
> massive, its luminosity and temperature are both steadily decreasing.
>
> Are you concerned that it shouldn't be in contact yet?  What is happening
> to the primary?  I would have expected the integration to stop when the
> primary became a giant.
>
> Maybe that helps.  I didn't have the chance to try your inlists.
>
> Dean
>
>  On 12/10/2014 05:28 PM, 이현택 wrote:
>
>  Dear MESA users,
>
>  I have some questions regarding numerical model of binary star
> simulation.
>
>
>  1)
> During the low mass binary simulation,(1.0 solar mass and 0.8 solar mass
> with orbital period of 2 days)
> for the primary star (1 solar mass) it seems that there is no problem. But
> for secondary star, at some point (around 5 Gyrs) all the abundances
> becomes constant.
>
>  2)
> Along with the abundance issue, the HR diagram shows only the decreasing
> tendency of luminosity and surface temperature.
> (i.e. the luminosity and surface temperature only decreases)
>
>
>  Please refer to the attached inlist files and png files which shows the
> issues.
>
>
>  What can possibly be the physical meaning of this situation?
> I wonder whether star can interchange their mass by stellar wind before
> filling Roche lobe.
> And I'd like to know how mesa numerically distinguishes the Roche lobe and
> the star.
>
>  What is the computational implementation of Roche lobe?
>
>
>  Thanks in advance.
>
>  Sincerely yours, HYUN TAEK-
>
>
>
>
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-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD student, Argelander-Institut für Astronomie
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