[mesa-users] Module binary_mdot.f, eddington accretion bug

[Pablo Marchant]

Hi Mads.

The additional options for mdot_edd have been added to MESA, and should be
available for use on the next release.

Cheers!

On Fri, Feb 6, 2015 at 11:48 AM, Mads Sorensen <Mads.Sorensen at unige.ch>
wrote:

>  Hi Pablo,
>
>  I think it sounds good and it would work for me. The importance is the
> flexibility and keeping the code within the MESA spirit.
>
>  Mads
>
>  On 5 Feb 2015, at 20:44, Pablo Marchant <pamarca at gmail.com> wrote:
>
>  Hi Mads, Pablo here, I do most of the coding in the binary module these
> days.
>
>  As with most of MESA, I think the best here would be to provide several
> options. An easy built one option could be to compute the Eddington rate
> using the Thompson scattering opacity associated to the composition at the
> surface of the star, or the opacity at the outermost cell (user decides).
> For more specific models like the one you say, we can provide hooks so that
> mdot_edd can be anything that you want. This is also significantly more
> flexible than just changing the default.
>
>  Would that work for you?
>
> On Thu, Feb 5, 2015 at 10:15 AM, Mads Sorensen <Mads.Sorensen at unige.ch>
> wrote:
>
>>  Hi,
>>
>>  In MESA-r7184 module binary_mdot.f line 282 states the Eddington
>> accretion using the opacity of the donor star most outer layer which is
>> probably a good solution for mass tranfers between two stars.
>> When conducting mass transfer sequences involving compact objects like
>> black holes, i.e. x-ray binaries, the current solution fails to account for
>> the conditions of the accretion disc. Under these conditions a more likely
>> formulation would be to use the Thompson scattering opacity and radiation
>> efficiency $\eta$ = 0.1 assuming an accretion disc of mostly hydrogen.
>>
>> We have tested a new formulation using eq. 1.4 and 1.9 of Frank, King,
>> and Raine, 2002, Accretion power in astrophysics, against the previous
>> model. In short the new formulation allows a higher accretion rate onto the
>> compact object and will therefore have an effect on the overall mass
>> transfer in the binary system relative to the current formulation.
>>
>> Current line 282 in binary_mdot.f:
>> mdot_edd = 4*pi*b% s1% cgrav(1)*b% m(b% a_i)/(clight*b% s1% opacity(1))
>>
>> New suggestion to line 282 in binary_mdot.f which we have used:
>>
>> mdot_edd = 1.3d0*1.d38 * b% m(b% a_i)/msol  /(clight**2*0.1d0)
>>
>> Enclosed are examples of runs using the current and new formulation of
>> the Eddington accretion rate and a run with no limit to the accretion rate
>> - see the plot title inside.
>> The run is the binary/test_suite donor only implicit mdot simulation with conservative
>> mass transfer of a donor of 8 Msun, accretor of 6 Msun, and initial period
>> of 1 day, inlist files are also attached.
>>
>>
>> With my best regards,
>>
>> Mads Sørensen,
>> Candoc/Doctorant/PhD student
>> Observatoire Astronomique
>> Geneva University
>>
>>
>>
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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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