Study of classical be stars in open clusters in the galaxy

Abstract

Classical Be stars (CBe) in open clusters older than 100 Myr are identifed. The objective is to study their characteristics relating to age, spectral type and evolutionary state. This study compliments with that of Mathew et al. (2008), where they identifed and characterized emission-line stars in open clusters younger than 100 Myr. For this research, we surveyed a sample of newline71 open clusters older than 100 Myr using the slitless spectroscopy technique, with the Himalayan Chandra Telescope (HCT). From the survey we identifed 15 CBe stars from the 11 open clusters older than 100 Myr. Out of 15 CBe stars, 13 CBe stars show Hand#945; in emission. Among these CBe stars, TYC 2679-432-1 is a new detection, belonging to Berkeley 50 open newlinecluster. Two more CBe stars, out of 15 CBe stars, are found to exhibit Hand#945; in absorption for the frst time. This suggests that they might be passing through a disc-loss episode (or transient phase). Apart from our survey of 71 old open clusters, we found additional 16 Be stars from 6 open clusters older than 100 Myr in the literature (which was not observed in the slitless survey due to observation limitations). In addition to HFOSC instrument mounted on HCT, we used Opto Mechanics Research (OMR) spectrograph newlinemounted on 2.3-m Vainu Bappu Telescope (VBT) for taking the slit spectra of CBe stars. We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 Myr. Among these 16 stars, 15 newlinewere identifed from our previous slitless spectroscopic study. The remaining one, LS III +47 37b is a new detection, which is confrmed through the present study. Our analysis also suggests that one out of these 16 stars, [KW97] 35-12 might be a weak Hand#945; emitter in nature showing Hand#945; EW of -0.5 Å. Moreover, it is found that the Hand#945; EW for 15 stars is lt -40 Å, in agreement with previous works. Interestingly, we did not observe any FeII emission line or even the OI 8446 Å emission feature in any of our sample stars.