Ultraviolet observations of the hydrogen-deficient variable star MV Sagittarii

Abstract

IUE observations of the hydrogen-deficient irregular variable star MV Sgr obtained in June-October 1980 and November 1979 are discussed. The observations reveal a prominent 2200 A absorption feature. A value of E(B - V) = 0.55 is deduced from the strength of the 2200 A band on the assumption that this absorption is caused by an interstellar medium. It is noted that the dereddened continuum obtained at different times can be fitted to a theoretical energy distribution of a helium star mode with an effective temperature of 18000 K and log g = 2.5, similar to that of BD + 10 deg 2179. After applying interstellar extinction, this theoretical energy distribution gives V = 12.7 mag, agreeing with the observed visual magnitude of about 13 in November 1979 and June-October 1980. Despite the absence of change in the continuum flux, the ultraviolet line-spectrum shows variations.