Re: [mesa-users] Angular momentum loss due to winds

[Glenn-Michael O. <gle...@ku...>]

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.

Cheers,
Glenn


________________________________
Van: Pablo Marchant <pa...@gm...>
Verzonden: donderdag 27 juli 2017 05:08
Aan: Glenn-Michael Oomen
CC: mes...@li...
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 <gle...@ku...<mailto:gle...@ku...>> 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: mes...@li...<mailto:mes...@li...>
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