The orbit and spectral line variations of the massive binary HD 163181 (V453 scorpii)

We present revised orbital elements for the massive interacting binary HD 1 63181, and we offer the first evidence of apsidal motion in the orbit (apsi dal period U = 510 +/- 100 yr). We searched for but found no obvious eviden ce of the secondary's spectral lines in our optical spectra. We do observe, however, systematic profile variations with orbital phase that probably re sult from a gas stream from the Roche lobe-filling supergiant to the faint secondary. The relatively small projected rotational velocity of the primar y (V sin i = 88 +/-3 km s(-1)), the faintness of the secondary, the reporte d lack of orbital motion in the H alpha emission, and the presence of an IR excess all suggest that the system is surrounded by an extensive circumbin ary disk (as is found in a similar binary, RY Scuti).