Abstract
ABSTRACT. A group of non-variable yellow supergiants were observed with the International Ultraviolet Explorer satellite, with the aim of discovering hot companions. Four newly discovered systems are announced: HD 26630 (G0Ib+B9-9.5), HD 74395 (G2I+B9.5), HD 193469 (F5Ib+B4-5), and the Cepheid HD 129708 (F2II+B4-5). The Cepheid HD 9250 was observed but no hot companion was found. Some stars known to have a hot companion were also included to study the properties of the companion and to compare with previous work. Kurucz's (1979) atmospheric ::odels were used to fit the overall energy distribution of the binary system and allowed to estimate Te, log g and the spectral type of the hot companion. The magnitude differences in the V band between the yellow supergiants and their companions were calculated. This provides a way of estimating Mv for yellow supergiants and the distance to the systems. Comparison with evolutionary tracks, suggest that the masses of the primaries are contained between 5 and 9 M⊙ and that, on average, they are about twice as massive. Details will be published elsewhere.
