Spectroscopy of Be stars in young open clusters

Blesson Mathew1,2* and Annapurni Subramaniam1
1Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
2Department of Physics, Calicut University, Calicut, Kerala, India

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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 Hβ. Classical Be stars with higher Balmer decrement (76%) were found to have more number of emission lines, higher Hα 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 Hα 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.

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Keywords : stars: formation - stars: emission-line, Be - stars: open clusters.