EDP Sciences
Free access
Volume 440, Number 2, September III 2005
Page(s) 511 - 522
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20052683

A&A 440, 511-522 (2005)
DOI: 10.1051/0004-6361:20052683

NGC 146: a young open cluster with a Herbig Be star and intermediate mass pre-main sequence stars

A. Subramaniam1, D. K. Sahu2, R. Sagar3 and P. Vijitha4

1  Indian Institute of Astrophysics, II Block Koramangala, Bangalore 560034, India
    e-mail: purni@iiap.res.in
2  CREST Campus, Indian Institute of Astrophysics, Hosakote, Bangalore, India
    e-mail: dks@crest.ernet.in
3  Aryabhatta Research Institute of Observational Studies (ARIES), Manora peak, Nainital 263129, India
    e-mail: sagar@upso.ernet.in
4  VSRTP Student, Mother Theresa University, Kodaikanal, India

(Received 12 January 2005 / Accepted 11 May 2005)

We present UBV CCD photometry and low-resolution spectra of stars in the field of the young open cluster NGC 146. UBV photometry of 434 stars were used to estimate the E(B-V) reddening of 0.55 $\pm$ 0.04 mag and BV photometry of 976 stars were used to estimate a distance modulus of (m-M)0 = 12.7 $\pm$ 0.2 mag, corresponding to a distance of 3470 +335-305 pc. We estimated 10-16 Myr as the turn-off age for the upper main sequence of the cluster using isochrones and synthetic colour magnitude diagrams. We identified two B type stars with H$_\alpha$ in emission and located on the MS using slit-less spectra. A higher resolution spectrum of the brighter Be star indicated the presence of a number of emission lines, with some lines showing the signature of gas infall. This star was found to be located in the region of Herbig Ae/Be stars in the (J-H) vs. (H-K) colour-colour diagram. Thus, we identify this star as a Herbig Be star. On the other hand, 54 stars were found to show near infrared excess, of which 17 were found to be located in the region of Herbig Ae/Be stars and 18 stars were found to be located in the region of Be stars in the NIR colour-colour diagram. Thus NGC 146 is a young cluster with a large number of intermediate mass pre-main sequence stars. The turn-on age of the cluster is found to be ~3 Myr. Though NGC 146 shows an older turn off, the bulk of stars in this cluster seems to belong to the younger population of 3 Myr.

Key words: Galaxy: open cluster and associations: individual: NGC 146 -- stars: emission-line, Be -- stars: Hertzsprung-Russell (HR) and C-M diagrams -- stars: pre-main sequence

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