Testing Binary Population Synthesis Models with Hot Subdwarfs

Models of binary star interactions have been successful in explaining the origin of field hot subdwarf (sdB) stars in short period systems, but longer–period systems that formed via Roche– lobe overflow (RLOF) mass transfer from the present sdB to its companion have received less attention. We map sets of initial binaries into present–day binaries that include sdBs and main– sequence stars, distinguishing “observable” sdBs from “hidden” ones. We aim to find out whether (1) the existing catalogues of sdBs are sufficiently fair samples of all the kinds of sdB binaries that theory predicts; or instead whether (2) large predicted hidden populations mandate the construction of new catalogues, perhaps using wide–field imaging surveys such as 2MASS, SDSS, and Galex. We also report on a pilot study to identify hidden subdwarfs, using 2MASS and GALEX data.