ABSOLUTE DIMENSIONS AND MASSES OF ECLIPSING BINARY STARS - THE ANOMALOUS TRIPLE STAR V909 CYGNI

V909 Cygni is found to be a triple star (A0+A2+A1) with some anomalous properties. The A0+A2 eclipsing binary has a very small primary for i ts mass, although, within the observational errors, it; is not inconsi stent with a zero-age star according to some models. The secondary sta r of the eclipsing binary, however, is less massive but considerably l arger than the primary. Since the binary is well detached, mass exchan ge looks unlikely as an explanation. It may be that the secondary is a pre-main-sequence object. The observed rotational velocities are sign ificantly faster than synchronous, which would be expected if the seco ndary star were as young as a pre-main-sequence object. This system de serves further study. (C) 1997 American Astronomical Society.