2MASS photometry of hot subdwarf stars

This sample size greatly exceeds that of previous studies of hot subdwarfs. Examining 2MASS photometry alone or in combination with visual photometry (Johnson BV or Stroemgren uvby) available in the literature, we show that it is possible to identify hot subdwarf stars that exhibit atypically red IR colors, which can be attributed to the presence of an unresolved late-type companion.

Utilizing this large sample, we attempt for the first time to define an approximately volume-limited sample of hot subdwarfs. We discuss the considerations, biases, and difficulties in defining such a sample. We find that, of the hot subdwarfs in Kilkenny et al. (1988SAAOC..12....1K), about 40% in a magnitude-limited sample have colors that are consistent with the presence of an unresolved late-type companion.