Kepler as a Binary Star Mission

Abstract

The Kepler observatory was designed to discover transits by Earth‐like planets orbiting Sun‐like stars. Its first major discoveries, however, are hot objects in close orbits around main‐sequence stars. These are likely to be white‐dwarf remnants of stars that have transferred mass to the present‐day main sequence stars. These particular main‐sequence stars are among the Kepler targets because they are bright. The question is: how many of the other Kepler target stars are also orbited by white dwarfs? We have shown that several hundred white dwarfs are likely to transit the Kepler target stars during the mission. In some cases, the signature will be dominated by gravitational lensing, producing distinctive “antitransits”. Neutron stars and black holes may also be discovered this way. The lensing signature provides a measurement of the gravitational mass of the compact object. Through the discovery of both transits and antitransits caused by white dwarfs, Kepler will discover and study binaries that have already experienced a phase of mass transfer or a common envelope phase. Thus, Kepler will become a premier tool for the study of interacting binaries. During the next phase of interaction, some of the Kepler binaries may become nuclear‐burning white dwarfs, and may be candidates for Type Ia supernovae or accretion‐induced collapse.