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

Abstract

We present UBV CCD photometry and low-resolution spectra of stars in the field of the young open cluster NGC 146.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 Hα 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.