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

[Jim Fuller]

Here is an inlist from a binary model I made that evolved stably through
the period minimum. I'm not sure which combination of different parameters
allowed MESA to get through it, but maybe it will help you out.
-Jim

On Wed, Sep 2, 2020 at 4:47 PM Kareem El-Badry <kelbadry at berkeley.edu>
wrote:

> 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
>>>
>>> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
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