Contact binaries . III. Early-type systems.

Abstract

About 1000 (u,v,b,y, ß) observations of some 60 early-type contact systems are discussed. The photometric indices for most of the stars show little variation and are given in summary form, while graphical presentation is used for a few typical systems or systems of special interest. Two or three objects may not be eclipsing systems, including VV Scl, which may be the first "magnetic" variable discovered photograpically. Loci in the ([u-b ], M v) plane for 0.75-, 1.5-, and 3.0-day contact binaries are constructed from evolutionary models of 4-, 6-, 8-, 12-, 15-, and 2O-M 0 stars. Most of the field variables are reasonably well reproduced by these models and estimates of their age are therefore available. Three contact binaries in the very young clusters IC 2994 and NGC 6383 and a detached system in NGC 6871 are also discussed, together with the other cluster members. Certainly contact systems, and perhaps detached systems, occur in the pre-main-sequence contraction phase of stellar evolution but there is an enigma in that the "degree of contact" for such systems may be much greater than for post-main-sequence binaries. Several systems of special interest are discussed including SU Psc, 6 kpc from the galactic plane and only about 3xl0 7 years old; V505 Mon, a supergiant with a period believed to be less than 1 day; RZ Pyx and VW CMa, which may be examples of pre-main-sequence systems; XX Ant, which may comprise highly evolved, F-type giants; V701 Cen, which was discovered to be a close visual binary; V327 Aql, which is found to be composed of supergiants and not dwarfs as indicated by spectroscopic studies; and LW Cen, a contact binary in the very young cluster IC 2994, which has a period near 1 day and may be undergoing some structural change.