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We have found a system listed in the Kepler Binary Catalog (3.273 day period;Prsa et al. 2010) that we have determined is comprised of a low-mass,thermally-bloated, hot white dwarf orbiting an A star of about 2.3 solarmasses. In this work we designate the object, KIC 10657664, simply as KHWD3. Weuse the transit depth of ~0.66%, the eclipse depth of ~1.9%, and regular smoothperiodic variations at the orbital frequency and twice the orbital frequency toanalyze the system parameters. The smooth periodic variations are identifiedwith the classical ellipsoidal light variation and illumination effects, andthe newly utilized Doppler boosting effect. Given the measured values of R/aand inclination angle of the binary, both the ELV and DB effects are mostlysensitive to the mass ratio, q = M_2/M_1, of the binary. The two effects yieldvalues of q which are somewhat inconsistent - presumably due to unidentifiedsystematic effects - but which nonetheless provide a quite useful set ofpossibilities for the mass of the white dwarf (either 0.18 +/- 0.03 M_Sun or0.37 +/- 0.08 M_Sun). All of the other system parameters are determined fairlyrobustly. In particular, we show that the white dwarf has a radius of 0.15 +/-0.01 R_Sun which is extremely bloated over the radius it would have as a fullydegenerate object, and an effective temperature T_eff = 14,100 +/- 350 K.Binary evolution scenarios and models for this system are discussed. We suggestthat the progenitor binary was comprised of a primary of mass ~2.2 M_Sun (theprogenitor of the current hot white dwarf) and a secondary of mass ~1.4 M_Sun(the progenitor of the current A star in the system). We compare this newsystem with three other white dwarfs in binaries that likely were formed viastable Roche-lobe overflow (KOI-74, KOI-81, and Regulus).

A Third Hot White Dwarf Companion Detected by Kepler