  The observed Galactic rate of stellar mergers or the initiation of common
envelope phases brighter than M_V=-3 (M_I=-4) is of order 0.5 (0.3)/year with
90% confidence statistical uncertainties of 0.24-1.1 (0.14-0.65) and factor of
2 systematic uncertainties. The (peak) luminosity function is roughly dN/dL
L^(-1.4+/-0.3), so the rates for events more luminous than V1309 Sco (M_V=-7
mag) or V838Mon (M_V=-10 mag) are lower at r~0.1/year and 0.03/year,
respectively. The peak luminosity is a steep function of progenitor mass, L
M^(2-3). This very roughly parallels the scaling of luminosity with mass on the
main sequence, but the transients are ~2000-4000 times more luminous at peak.
Combining these, the mass function of the progenitors, dN/dM M^(-2.0+/-0.8), is
consistent with the initial mass function, albeit with broad uncertainties.
These observational results are also broadly consistent with the estimates of
binary population synthesis models. While extragalactic variability surveys can
better define the rates and properties of the high luminosity events,
systematic, moderate depth (I>16 mag) surveys of the Galactic plane are needed
to characterize the low luminosity events. The existing Galactic samples are
only ~20% complete and Galactic surveys are (at best) reaching a typical
magnitude limit of <13 mag.
