  Most of the X-ray emitting gas in early-type galaxies probably originates
from red giant mass loss and here we model the interaction between this stellar
mass loss and the hot ambient medium. Using two-dimensional hydrodynamic
simulations, we adopt a temperature for the ambient medium of 3E6 K along with
a range of ambient densities and stellar velocities. When the stellar velocity
is supersonic relative to the ambient medium, a bow shock occurs, along with a
shock driven into the stellar ejecta, which heats only a fraction of the gas.
Behind the bow shock, a cool wake develops but the fast flow of the hot medium
causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and
heated (without radiative cooling). Along with the mixing of this wake material
with the hot medium, most of the stellar ejecta is heated to approximately the
temperature of the hot ambient medium within 2 pc of the star. With the
addition of radiative cooling, some wake material remains cool (< 1E5 K),
accounting for up to 25% of the stellar mass loss. Less cooled gas survives
when the ambient density is lower or when the stellar velocity is higher than
in our reference case. These results suggest that some cooled gas should be
present in the inner part of early-type galaxies that have a hot ambient
medium. These calculations may explain the observed distributed optical
emission line gas as well as the presence of dust in early-type galaxies.
