TOWARD UNDERSTANDING THE B[e] PHENOMENON. I. DEFINITION OF THE GALACTIC FS CMa STARS

Q1 The B[e] phenomenon is defined as the simultaneous presence of low-excitation forbidden line emission and strong infrared excess in the spectra of early-type stars. It was discovered in our Galaxy 30 years ago in the course of the early exploration of the infrared sky and initially identified in 65 Galactic objects, of which nearly half remained unclassified. The phenomenon is associated with objects at different evolutionary stages, ranging from the preYmainsequence to the planetary nebula stage. We review the studies of both the original 65 and subsequently identified Galactic stars with the B[e] phenomenon. A new classification is proposed for stars with the B[e] phenomenon based on the time of dust formation in their environments. Properties of the unclassified Galactic B[e] stars are analyzed. We propose that these objects are binary systems that are currently undergoing or have recently undergone a phase of rapid mass exchange, associated with a strong mass loss and dust formation. A new name, FS CMa stars, and classification criteria are proposed for the unclassified B[e] stars. Subject headinggs: circumstellar matter — stars: early-type — stars: emission-line, Be