Commission 42: Close Binary Stars: ( Etoiles Doubles Serrees )

This is the last triennial report of Commission 42 for this millennium. A great deal has been accomplished in the study of Close Binary Stars(CBS) since the discovery of the first close ( eclipsing) binary, Algol, in 1783 by John Goodricke. Now, over 10,000 CBS (most eclipsingvariables) are known. More than 5000 of these CBS were discovered over the last several years alone! And many more are expected to be detected over the next few years. Most of these starswere found as spin-offs of microlensing surveys. Interestingly, nearly half of these starsare found outside our Galaxy, primarily in the Magellanic Clouds and M31. Every type of staris represented as a member of a close binary. These include main sequence(as well as pre-main sequence) stars, giants, and supergiants, with the entire possible range of of spectral types and masses represented. Moreover, “dying” starsand “dead” stars, such as white dwarfs, neutron stars, black holes, and, more recently, even brown dwarfsand giant planets(e.g., 51 Peg) have been found as members of close binary systems.