  We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda
galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare
hydrogen-deficient, carbon-rich supergiant variables, most likely the merger
products of two white dwarfs. These new RCBs, including two confirmed ones and
two candidates, are the first to be found beyond the Milky Way and the
Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over
timescales of weeks to months. Due to the limiting magnitude of our data
(R~21-22 mag), these RCB stars have R~19.5 to 20.5 mag at maximum light,
corresponding to M_R= -4 to -5, making them some of the most luminous RCBs
known. Spectra of two objects show that they are warm RCBs, similar to the
Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a
pilot study of M31 variables, as an important proof-of-concept for the study of
rare bright variables in nearby galaxies with the PTF or other synoptic
surveys.
