THE SUPERGIANT BINARY BM CAS

Attracted by an earlier claim (Thiessen 1956, ZfAp, 39, 65) that BM Ca s is an eclipsing binary with one component a classical Cepheid, we ha ve 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 variabili ty 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 comp onent. We find the latter to be a high-luminosity star of spectral typ e of A6, in close agreement with the MK assignment of A7 Iab (Bidelman 1982, IBVS, No. 2112), and the secondary component to most likely be a late-K or early-M giant. The latter appears; to fill or nearly fill its Roche lobe, while the primary star is not far from doing so as wel l, implying a complex evolutionary history for the system.