Optical Spectroscopy of Classical Be Stars in Old Open Clusters

Abstract

This is the first spectroscopic study of CBe stars in open clusters older than 100 Myr. We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 Myr. Among these 16 stars, we identified 15 stars from our previous slitless spectroscopy study. The remaining one, LS III +47 37b, is a new detection, which is confirmed through the present study. We found that the Hα emission strength of most of the stars is less than 40 ̊A, in agreement with the previous studies. Our analysis also suggests that one out of these 16 stars, [KW97] 35-12, might be a weak Hα emitter in nature showing Hα EW of -0.5 ̊A. Interestingly, we also found that these 16 stars exhibit lesser number of emission lines compared to classical Be stars younger than 100 Myr. Moreover, the spectral type distribution analysis of B-type and classical Be stars for selected clusters points out that there might be a probability that the existence of classical Be stars can depend on the incidence of B-type stars present in the respective clusters.