2001PASP..113..957J

We present revised orbital elements for the massive interacting binary HD 163181, and we offer the first evidence of apsidal motion in the orbit (apsidal period U=510±100 yr). We searched for but found no obvious evidence of the secondary's spectral lines in our optical spectra. We do observe, however, systematic profile variations with orbital phase that probably result from a gas stream from the Roche lobe-filling supergiant to the faint secondary. The relatively small projected rotational velocity of the primary (Vsini=88±3 km.s^–1), the faintness of the secondary, the reported lack of orbital motion in the Hα emission, and the presence of an IR excess all suggest that the system is surrounded by an extensive circumbinary disk (as is found in a similar binary, RY Scuti).