Study of emission line stars in young open clusters

Blesson Mathew11* and Annapurni Subramaniam1
1Indian Institute of Astrophysics, Bangalore 560034, India

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Emission-line stars in young open clusters are identified to study their properties, as a function of age, spectral type and evolutionary state. 207 open star clusters were observed using the slitless spectroscopy method and 157 emission stars were identified in 42 clusters. We have found 54 new emission-line stars in 24 open clusters, out of which 19 clusters are found to house emission stars for the first time. The Classical Be (CBe) stars are located all along the main sequence (MS) in the optical colour magnitude diagram (CMD) of clusters of all ages, which indicates that the Be phenomenon is unlikely only due to core contraction near the turn-off. A spectroscopic study of 152 CBe stars in 42 young open clusters was performed using medium resolution spectra in 3700 - 9000 Å range, to understand the Be phenomenon. Stars in the B0 - B2 spectral bin are found be spun up towards the end of their MS life time, suggesting that early type stars evolve to become Be stars. Similar variation in properties were not found for stars in the later spectral types (B4 - A0), suggesting that the Be phenomenon differs in early type and late type stars. Spectroscopic studies were done for the identified Herbig Ae/Be (HAeBe) stars. The starformation history of the hosting cluster was estimated by identifying pre- MS stars. The ages of HAeBe stars were estimated. The duration of star formation in the hosting cluster were found to be about 10 Myr.

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Keywords : stars: formation – stars: emission-line, Be – stars: pre-main sequence – : (Galaxy:) open clusters and associations: general – surveys