  The Kepler Mission has acquired 33.5d of continuous one-minute photometry of
KPD 1946+4340, a short-period binary system that consists of an sdB and a white
dwarf. In the light curve, eclipses are clearly seen, with the deepest
occurring when the compact white dwarf crosses the disc of the sdB (0.4%) and
the more shallow ones (0.1%) when the sdB eclipses the white dwarf. As
expected, the sdB is deformed by the gravitational field of the white dwarf,
which produces an ellipsoidal modulation of the light curve. Spectacularly, a
very strong Doppler beaming (aka Doppler boosting) effect is also clearly
evident at the 0.1% level. This originates from the sdB's orbital velocity,
which we measure to be 164.0\pm1.9 km/s from supporting spectroscopy. We
present light curve models that account for all these effects, as well as
gravitational lensing. We derive system parameters and uncertainties from the
light curve using Markov Chain Monte Carlo simulations. Adopting a theoretical
white dwarf mass-radius relation, the mass of the subdwarf is found to be
0.47\pm0.03 Msun and the mass of the white dwarf 0.59\pm0.02 Msun. The
effective temperature of the white dwarf is 15 900\pm300K. With a spectroscopic
effective temperature of Teff = 34 730\pm250K and a surface gravity of log g =
5.43\pm0.04, the sdB is in a shell He burning stage. The detection of Doppler
beaming in Kepler light curves potentially allows one to measure radial
velocities without the need of spectroscopic data. For the first time, a
photometrically observed Doppler beaming amplitude is compared to a
spectroscopically established value. The sdB's radial velocity amplitude
derived from the photometry 168\pm4 km/s is in perfect agreement with the
spectroscopic value. After subtracting our best model for the orbital effects,
we searched the residuals for stellar oscillations but did not find any
significant pulsation frequencies.
