Recent Progress in Finding Binary Systems with the B[e] Phenomenon

This paper describes recent studies of the FS CMa-type objects, a group of stars showing the B[e] phenomenon defined in 2007. The objects exhibit strong emission-line spectra with both permitted and forbidden lines suggesting the presence of a B-type star as well as strong IR excesses due to radiation of circumstellar dust. These properties are hard to explain in the framework of the evolution of single stars with luminosities between similar to 300 and similar to 30,000 L-circle dot typical of most B-type stars. We explore the hypothesis that the gaseous-and-dusty envelopes of FS CMa objects are due to either earlier or ongoing mass transfer between the binary system components. It is hard to detect the secondary components in these systems because of veiling and distortions by the circumstellar matter because of the relative faintness of the companions. Nevertheless, we detected regular radial velocity variations of the spectral lines in MWC 728, 3 Pup, and AS 386 and we found absorption lines typical of cool stars in the spectra of MWC 645, AS 174, and several other objects. The diversity of the secondary components in FS CMa objects is discussed in the context of non-conservative binary evolution.

Automated summary

This paper describes recent studies of the FS CMa-type objects, a group of stars with B[e] phenomenon defined in 2007. These objects exhibit strong emission-line spectra and IR excesses, which are difficult to explain in the framework of single star evolution. The hypothesis of mass transfer between binary system components is explored to explain the gaseous-and-dusty envelopes of FS CMa objects. Regular radial velocity variations and absorption lines of cool stars have been detected in some objects.