Blesson Mathew 1, Annapurni Subramaniam 1 and
B.Bhavya2
Abstract.
We present the spectroscopic study of 5 Herbig Ae/Be
stars
in young open clusters. These are identified from a survey of
emission-line
stars in young open clusters. The Herbig Ae/Be stars are found to show a
linear correlation in Hα equivalent width versus reddening corrected
(H−Ks )
colour plot, with a clear offset from the distribution of Classical Be
stars. The
candidates are found to show near infrared excess which was revealed
through
de-reddened (J−H) versus (H−Ks ) colour-colour diagram and spectral
energy
distribution. From optical/near-IR photometry and spectroscopy, we
suggest
that Bochum 6-1, IC 1590-1 and NGC 6823-1 are Herbig Be while IC 1590-2
and
NGC 7380-4 are Herbig Ae candidates. Bochum 6-1 is an interesting Herbig
B[e]
star with a high Hα equivalent width of −206 ̊, which is the highest
among the
A
surveyed stars. We combined the optical and near-IR photometry to
estimate
the duration of star formation in the clusters, Bochum 6, IC 1590, NGC
6823
and NGC 7380. We found ongoing star formation in all these clusters,
with
an appreciable number of pre-main sequence stars. The age of these
Herbig
Ae/Be stars, estimated using pre-main sequence isochrones, were found to
range
between 0.25−3 Myr. IC 1590 is found to be an interesting young cluster
(∼
4 Myr) with 3 emission stars, each belonging to Herbig Ae, Herbig Be and
Classical Be respectively. All the four clusters studied here were found
to be
forming stars for the last 10 Myr.
Keywords: stars: formation – stars: emission-line, Be
– stars: pre-main sequence – : open clusters
1Indian Institute of Astrophysics, Bangalore 560 034,
India
2Cochin University of Science and Technology, Cochin, Kerala