Abstract

A spectroscopic study of 152 Classical Be stars in 42 young open clusters was performed using medium resolution spectra in 3700-9000 Å range, to understand the Be phenomenon. The Balmer decrement is found to have a bimodal distribution which is correlated with the nature of H_β. Classical Be stars with higher Balmer decrement (76%) were found to have more number of emission lines, higher H_α equivalent width and (H-K)₀ values, suggesting an optically and geometrically thick disk. Massive Be stars of spectral type B0-B4 are found to have enhanced H_α emission at the end of their main sequence lifetime, as inferred from the enhancements observed at 12.5 and 25 Myr. These results support our earlier prediction that early B-type stars (B0-B4) spin up to Be phase while others (B4-A0) are born as Be stars.