The early-type component in v1 Sagittarii

Abstract

Four low-resolution UV spectra of v1 Sgr (cK2) were obtained with the IUE satellite to investigate the nature of the hot component in this object, which was detected in the Astronomical Netherlands Satellite UV photometric data. The IUE results show that the spectral energy distribution of v1 Sgr in the FUV is comparable to that of a B9 star. FUV flux level, when compared with that of the mid-ultraviolet flux level, indicates that the luminosity of the hot component is roughly equivalent to that of a main-sequence star, assuming that the mid-ultraviolet flux is dominated almost entirely by a K2 I object. No discernible spectral features are present in the FUV, contrary to what may be expected in a star of B9 spectral type. Two possible interpretations are suggested: the hot component is a rapidly rotating star, or an accretion disk surrounding a central object which could be a collapsed star is being observed.