The ultraviolet study of B[e] stars: evidence for pulsations, LBV-type variations, and processes in envelope

Abstract

Stars with B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including presence of Balmer lines in emission, forbidden lines, and strong infrared excess due to the dust. The observations of emission lines indicate the illumination by ultraviolet ionizing source, which is a key part to understand the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and its correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including the light absorption by the disk, pulsations, LBV-type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is not present only in the disk but also above its plane. The flux and line variability is consistent with a two-component model of circumstellar environment composed of the dense disk and ionized envelope. The observations of B[e] supergiants show that many of these stars have nearly the same luminosity of about $1.9\times10^{5}\,L_\odot$ and similar effective temperature.Comment: 20 pages, accepted for publication in MNRA