[Mesa-users] runaway mass transfer in WD-WD binary

[Kareem El-Badry]

Hi Jim,

Thanks for the suggestion. You're right that the papers from which I got my
assumption that mass transfer should be stable assumed it was conservative.
My reasoning for using fully non-conservative mass transfer was that novae
should periodically blow the accreted material off the surface of the WD.
I'm not sure whether this occurs smoothly enough in practice for
non-conservative mass transfer to be a good approximation.

In any case, I did try running with mass_transfer_beta = 0, but I get
basically the same behavior, so I don't think this is the root of this
particular issue (at least, not the only one).


Best,
Kareem

On Wed, Sep 2, 2020 at 9:28 AM Jim Fuller <jfuller at caltech.edu> wrote:

> Hi Kareem,
>
> It sounds like the mass transfer is becoming unstable. It should be stable
> for conservative mass transfer, but you're using non-conservative mass
> transfer, and I think that usually is unstable for white dwarfs. Have you
> tried with conservative mass transfer, i.e., mass transfer beta = 0 ?
>
> -Jim
>
> On Wed, Sep 2, 2020 at 7:00 AM Kareem El-Badry <kelbadry at berkeley.edu>
> wrote:
>
>> Hello MESA users,
>>
>> I'm trying to simulate mass transfer from a low-mass He WD (0.13 Msun)
>> onto a point mass that represents a massive WD (1.1 Msun). Mass transfer
>> should be stable and the period should increase once mass transfer begins
>> [I think] because (a) the orbit expands when the He WD loses mass, and (b)
>> the radius of the He WD increases when it loses mass, reestablishing
>> contact with the Roche lobe at a longer period.
>>
>> However, in the MESA calculations, Mdot gets very large as soon as the He
>> WD overflows its Roche lobe, and the calculation grinds to a halt. I've
>> attached inlists and a model.
>>
>> I am using version 12778.
>>
>> Some things I have tried:
>> - decreasing varcontrol_target and mesh_delta_coeff
>> - decreasing fm and fr
>> - setting set_to_this_tau_factor = 30
>> - turning off diffusion
>>
>>
>> But none of these had an appreciable effect. Does anyone have relevant
>> experience or an idea what the problem might be?
>>
>> Thanks,
>> Kareem
>>
>> _______________________________________________
>> mesa-users at lists.mesastar.org
>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>
>>
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