Rotation rates from Algol-type light curves - SW Cygni, AQ Pegasi, and AW Pegasi

Abstract

Exploitation of a recently developed means of deriving binary-component rotation rates from light curves is continued for three rapidly rotating Algol-type systems, which were selected for their known or suspected fast rotation, as part of a long-term program to improve the rotation statistics of Algols. The primary components of SW Cygni and AQ Pegasi appear to fill their limiting rotational lobes (i.e., the systems are double-contact binaries). The third binary, AW Pegasi is found to be close to double contact. An uncertainty common to all of these systems is that of whether the primary star's spectral lines are photospheric or due to orbiting gas. Comments are made concerning the expected effects of circumprimary gas on light-curve and line-profile estimates of rotation rates.