Identification of the companion stars of type Ia supernovae

The nature of the binary systems giving rise to Type Ia supernovae (SNe Ia) remains an unsolved problem. In this Letter, we calculate, from the statistics of initial conditions (masses and binary separations), the mass, luminosity, and velocity distributions of the possible binary companions (main-sequence star, subgiant, and red giant) following the explosion of the white dwarf that gives rise to the SNe Ia. Those companions could be detected from either their proper or their radial motions by means of high-precision astrometric and radial velocity measurements in young, nearby supernova remnants. Peculiar velocities typically ranging from 100 to 450 km s(-1) should be expected; these velocities place proper-motion measurements within reach of the Hubble Space Telescope instruments. Detections would solve the long-standing problem of which kinds of binaries produce SNe Ia and would clear the way for an accurate physical modeling of the explosions.