[mesa-users] Angular momentum loss due to winds

[Pablo Marchant]

On Jul 28, 2017 5:01 AM, "Glenn-Michael Oomen" <
glennmichael.oomen at kuleuven.be> wrote:

Hi Pablo,

The issue with the mdot_system_wind is indeed fixed in this way. I have
been working with it a couple days now together with the
other_binary_wind_transfer hook.

The absence of the Eddington limit is also a good catch, I hadn't thought
about that yet. Getting a proper framework for wind mass transfer in Mesa
is a good idea, since it is starting to become important in the evolution
of binaries with an evolved component.


Also, if you have simple examples that can be used to validate the
implementation of these processes, we could include them in the test_suite
such that they are automatically tested with each release.


To be honest, I am not really sure how the test_suite actually works. To
check whether the implementation works, I simply print stuff out. For the
example of the mdot_system_wind, I can give a specific mass loss rate of
the donor star and a specific wind accretion fraction, such that I exactly
know what the wind mass lost from the system should be...

Finally, I noticed you revamped the edot section in the newest version,
which is a great improvement. The previous fix in edot_tidal seems to be
reversed there, though. Another small issue is in
edot_enhancement_Isotropic, where edot_theta should be calculated with the
mass lost from the system instead of the total mass loss from the donor.
But I have the impression that this is still under construction, so it does
not matter that much.


Yes, I'm going through most of this code in detail now, and will be
building tests for it. Keep the bugfixes coming though! The reversal of
edot_tidal is a consequence of me having a thousand different copies of
MESA at the same time...

The idea for the test_suite is that if you know the result you should get
for a given system, one can check for that in run_star_extras. Analytical
results are the best for this, but a well established theoretical result
that can be loosely checked works as well.


Cheers,
Glenn


------------------------------
*Van:* Pablo Marchant <pamarca at gmail.com>
*Verzonden:* donderdag 27 juli 2017 05:08
*Aan:* Glenn-Michael Oomen
*CC:* mesa-users at lists.sourceforge.net
*Onderwerp:* Re: [mesa-users] Angular momentum loss due to winds

Hi Glenn-Michael, thanks for reporting this.

Version 9921 contains the fix you suggest, could you please verify it works
as you expect. Note that while changing this I noticed an additional error,
wind mass transfer is ignoring the Eddington limit. Depending on what
you're doing that could be an issue for you as well. Will try to fix it as
soon as I can.

Also, if you have simple examples that can be used to validate the
implementation of these processes, we could include them in the test_suite
such that they are automatically tested with each release.

Cheers

On Wed, Jul 12, 2017 at 4:41 AM, Glenn-Michael Oomen <
glennmichael.oomen at kuleuven.be> wrote:

> Note:
>
> Subtracting b% mdot_wind_transfer(b% d_i)​ should also do the trick.
> ------------------------------
> *Van:* Glenn-Michael Oomen
> *Verzonden:* woensdag 12 juli 2017 11:09
> *Aan:* mesa-users at lists.sourceforge.net
> *Onderwerp:* Angular momentum loss due to winds
>
>
> Hi Mesa,
>
>
> There might be a small problem with how the loss of angular momentum due
> to stellar winds is computed. It appears to me that b% mdot_system_wind is
> not actually the mass lost due to stellar winds from the system, but the total
> wind mass loss.
>
>
> So suppose I would for some reason impose a conservative wind mass
> transfer such that all the wind is transferred to the companion, then I
> would expect b% mdot_system_wind(b% d_i) to be zero, which is not the
> case. The bottom line is that this gives an overestimate for b% jdot_ml.
>
>
> The issue is in line 290 (and 293) in binary_evolve.f90, where b%
> mdot_system_wind appears to be defined simply as the wind mass loss of
> the star. I think that the whole equation should be multiplied by (1 - b%
> wind_xfer_fraction(s_i)) as to account for wind mass transfer to the
> companion and vice versa.
>
>
> Cheers,
>
> Glenn-Michael Oomen
>
>
>
>
>
>
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-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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