  In the limit of extremely rapid mass transfer, the response of a donor star
in an interacting binary becomes asymptotically one of adiabatic expansion. We
survey here adiabatic mass loss from Population I stars of mass 0.10 Msun to
100 Msun from the zero age main sequence to the base of the giant branch, or to
central hydrogen exhaustion for lower main sequence stars. For intermediate-
and high-mass stars, dynamical mass transfer is preceded by an extended phase
of thermal time scale mass transfer as the star is stripped of most of its
envelope mass. The critical mass ratio qad above which this delayed dynamical
instability occurs increases with advancing evolutionary age of the donor star,
by ever-increasing factors for more massive donors. Most intermediate- or
high-mass binaries with nondegenerate accretors probably evolve into contact
before manifesting this instability. As they approach the base of the giant
branch, however, and begin developing a convective envelope, qad plummets
dramatically among intermediate-mass stars, to values of order unity, and a
prompt dynamical instability occurs. Among low-mass stars, the prompt
instability prevails throughout main sequence evolution, with q_ad declining
with decreasing mass. Our calculated qad agree well with the behavior of
timedependent models by Chen & Han (2003) of intermediate-mass stars initiating
mass transfer in the Hertzsprung gap. Application of our results to cataclysmic
variables, as systems which must be stable against rapid mass transfer, nicely
circumscribes the range in qad as a function of orbital period in which they
are found. These results are intended to advance the verisimilitude of
population synthesis models of close binary evolution.
