Optical Spectroscopy of Classical Be Stars in Old Open Clusters

Abstract

We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 Myr. Ours is the first spectroscopic study of classical Be stars in open clusters older than 100 Myr. We found that the Hα emission strength of most of the stars is less than 40 Å, in agreement with previous studies. Our analysis further suggests that one of the stars, [KW97] 35–12, might be a weak Hα emitter in nature, showing Hα equivalent width of −0.5 Å. Interestingly, we also found that the newly detected classical Be star LS III +47 37b might be a component of the possible visual binary system LS III +47 37, where the other companion is also a classical Be star. Hence, the present study indicates the possible detection of a binary Be system. Moreover, it is observed that all 16 stars exhibit a lesser number of emission lines compared to classical Be stars younger than 100 Myr. Furthermore, the spectral type distribution analysis of B-type and classical Be stars for the selected clusters points out that the existence of CBe stars can depend on the spectral type distribution of B-type stars present in these clusters