The Supergiant Binary BM CAS

Abstract

Attracted by an earlier claim (Thiessen 1956) that BM Cas is an eclipsing binary with one component a classical Cepheid, we have obtained new photometry and IUE ultraviolet spectra of the system. While we verify that there is variability in addition to the eclipses, we conclude that there is no classical Cepheid present. The variability is irregular, and, since it is present in the uv spectra as well as in the V photometry, we believe it is associated with the hotter component. We find the latter to be a high-luminosity star of spectral type of A6, in close agreement with the MK assignment of A7 Iab (Bidelman 1982), and the secondary component most likely to be a late-K or early-M giant. The latter appears to fill or nearly fill it Roch lobe, while the primary star is not far from doing so as well, implying a complex evolutionary history for the syste. (SECTION: Stars)