Friday, February 19, 2010

Evolved Binaries

NASA’s Kepler space telescope was launched on 6 March 2009 with the primary objective of detecting Earth-like planets orbiting other stars. Amongst Kepler’s first major discoveries are two small objects which are hotter than the stars they orbit and both objects are likely to be very low mass white dwarfs. KOI-81b is estimated to be 40 percent as luminous as the Sun with a surface temperature of 13000 degrees Kelvin while KOI-74b is estimated to be 3 percent as luminous as the Sun with a surface temperature of 12000 degrees Kelvin. These objects are definitely not planets as they have surface temperatures an order of magnitude higher than would be consistent with stellar heating alone.

A paper by Rosanne Di Stefano (2010) entitled “Transits and Lensing by Compact Objects in the Kepler Field: Disrupted Stars Orbiting Blue Stragglers” describes the prospects of Kepler in discovering a large number of such objects as described above. These hot compact objects are most likely the cores of stars that have evolved to their present state through a process of stable mass transfer with their current stellar companions. Kepler offers a unique opportunity to study a large sample of such white dwarfs and the role of mass transfer in the evolution of binary star systems.