[mesa-users] Help: About mass eject duo to crit_V

[Pablo Marchant]

Wang, before I had directed you to the related example shown in the last
mesa paper. In that case it works as Josiah says, the required mass loss
rate is taken merely as the minimum required such that the star remains
just below critical. This is however very sensitive on what specific
angular momentum is lost in this way.

In MESA, mass loss in this case is just taking the angular momentum of the
outer shells of the star, which should be a safe lower limit. As Jiri
points out, losing material from a decrettion disk allows removal of more
angular momentum per unit mass, so a single star would in reality have
lower mass loss rates than those obtained by mesa in the way described
before.

The situation with a binary is more complicated though, if it is true that
all material transferred to a critically rotating accretor is lost from the
system (thats not a small if!), then losing material from a large disk will
enhance angular momentum loss from the system, causing mass transfer rates
to rise and thus increasing the required amount of mass loss from the
system.

So, you have two kinds of angular momentum loss you care about, spin and
orbital. Spin angular momentum is taken as the specific value of the outer
shells (which is less than that at the equator). Orbital angular momentum
is taken away with the specific orbital angular momentum of the accretor.
So there is no modelling of mass loss from a disk, if you want that you'll
need to do some work.

In MESA it is easy to adjust the amount of angular momentum lost to fit
your needs, as long as you know precisely how much angular momentum should
be lost. Just saying mass loss from a disc from a star at critical rotation
is very far from being a precise description. If you want more help on
making that work you will need to clearly state what you mean.
Am 25.09.2015 6:14 nachm. schrieb "Jiri Krticka" <
krticka at monoceros.physics.muni.cz>:

> Hello,
>
> On Fri, 25 Sep 2015, Josiah Schwab wrote:
>
> > For critical rotation mass loss, I believe Pablo has implemented
> > controls that removes just enough mass to bring model to below critical,
> > but it may still be experimental.  There is some note to this effect in
> > the docs
> >
> >  http://mesa.sourceforge.net/controls_defaults.html#premix_omega
> >
>
> Please note the outflowing disk forms at the critical rotation,
> consequently the star loses the angular momentum via the disk. The disk
> angular momentum scales with radius as R_disk^{1/2}, consequently the
> stellar mass-loss is scaled by a factor of (R_eq/R_disk)^{1/2} compared
> to the assumption that the mass-loss occurs at the stellar equator.
>
> http://adsabs.harvard.edu/abs/2011A%26A...527A..84K
>
> With best wishes,
>
> Jiri
>
>
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