Constraints on the Cessation of Eclipses in SS Lacertae and Their Implications for System Evolution

Abstract

SS Lac, a probable member of the open cluster NGC 7209, and a target system of several apsidal motion programs and of our binaries-in-clusters program for the past decade, is no longer eclipsing. The sudden disappearance of eclipses is now well documented. Zakirov and Azimov (IBVS 3487, 1990) and Schiller et al. (BAAS 23, 879, 1991) announced the current nonexistence of eclipses based on extensive photometry. Photographic and visual observations indicate cessation in the 1950–1951 season. Here we describe recent radial velocity work, modeling of published light curves, plans for further investigation and discuss implications of the cessation for system evolution.