R 81 : P CYG of the LMC.

Abstract

Photometric UBV observations and spectroscopic high dispersion coude observations of the very luminous B2.5 eq supergiant R 81 of the LMC carried out between 1970 and 1980 at ESO, La Silla, are discussed. It is noted that the most prominent features of the visual spectrum are P Cygni profiles of the Balmer lines, which are thought to indicate a shell with an expansion velocity of about 140 km/sec. The ultraviolet spectrum of R 81 is shown to be dominated by blue-shifted absorption resonance lines and Fe III absorption lines originating from metastable lower levels. From the UV resonance lines a very high mass loss rate is estimated. The early Balmer lines reveal very broad shallow emission wings, attributed to electron scattering. It is noted that the mass loss is highly variable and that it presumably occurs in the form of sudden ejections of discrete shells. Irregular brightness variations of a few tenths of a magnitude in V on timescales of weeks are found.