March 14
Abstract:
In an accreting system, the boundary layer is where matter slows down from
the orbital velocity in the disk to the rotation velocity of the star.
Because of the abruptness of this transition, large shears are generated
that can lead to distinctive instabilities that are sonic in nature. I
will discuss these instabilities and how they differ from shear
instabilities that operate under terrestrial conditions, such as the
Kelvin Helmholtz and Miles instabilities. I will also show movies from 2D
hydrodynamical simulations done with Athena of how these instabilities can
raise waves on the surface of the star and lead to trapped modes that are
stable for many hundreds of orbital periods. Such modes can in principle
lead to periodic variability in a light curve and may play a role in
explaining the variability observed in real astrophysical boundary layers,
such as dwarf nova oscillations.