Observations of Doppler Boosting in Kepler Lightcurves
  Among the initial results from Kepler were two striking lightcurves, for KOI
74 and KOI 81, in which the relative depths of the primary and secondary
eclipses showed that the more compact, less luminous object was hotter than its
stellar host. That result became particularly intriguing because a substellar
mass had been derived for the secondary in KOI 74, which would make the high
temperature challenging to explain; in KOI 81, the mass range for the companion
was also reported to be consistent with a substellar object. We re-analyze the
Kepler data and demonstrate that both companions are likely to be white dwarfs.
We also find that the photometric data for KOI 74 show a modulation in
brightness as the more luminous star orbits, due to Doppler boosting. The
magnitude of the effect is sufficiently large that we can use it to infer a
radial velocity amplitude accurate to 1 km/s. As far as we are aware, this is
the first time a radial-velocity curve has been measured photometrically.
Combining our velocity amplitude with the inclination and primary mass derived
from the eclipses and primary spectral type, we infer a secondary mass of
0.22+/-0.03 Msun. We use our estimates to consider the likely evolutionary
paths and mass-transfer episodes of these binary systems.
