  The asymptotic response of donor stars in interacting binary systems to very
rapid mass loss is characterized by adiabatic expansion throughout their
interiors. In this limit, energy generation and heat flow through the stellar
interior can be neglected. We model this response by constructing model
sequences, beginning with a donor star filling its Roche lobe at an arbitrary
point in its evolution, holding its specific entropy and composition profiles
fixed as mass is removed from the surface. The stellar interior remains in
hydrostatic equilibrium. Luminosity profiles in these adiabatic models of
mass-losing stars can be reconstructed from the specific entropy profiles and
their gradients. These approximations are validated by comparison with
time-dependent binary mass transfer calculations. We describe how adiabatic
mass loss sequences can be used to quantify threshold conditions for dynamical
time scale mass transfer, and to establish the range of post-common envelope
binaries that are allowed energetically.
