SCYON Abstract

Received on October 28 2001

A comprehensive study of the rich open star cluster NGC 2099 based on deep BVI CCD observations

AuthorsNilakshi & R. Sagar
State Observatory, Manora Peak, Nainital -- 263 129, India
Accepted byAstronomy & Astrophysics
Links NGC 2099, M37


The CCD observations of the rich open star cluster NGC 2099 and its surrounding field region have been carried out up to a limiting magnitude of V about 22 mag in B, V and I passbands for the first time. A total of about 12000 stars have been observed in the area of about 24 arcmin X 34 arcmin in the cluster region, as well as about 2180 stars in the 12 arcmin X 12 arcmin area of the field region located about 45 arcmin away from the cluster center. The cluster parameters determined by fitting the convective core overshoot isochrones in the V, (B-V) and V, (V-I) diagrams are E(B-V) = 0.30 ± 0.04 mag, distance = 1360 ± 100 pc, age = 400 Myr and metallicity Z = 0.008. A well-defined cluster main sequence spread over about 8 mag in range is observed for the first time. Its intrinsic spread amounting to about 0.06 mag in colour is almost the same over the entire brightness and can be understood in terms of the presence of physical/optical binaries. The core and cluster radii determined from the radial stellar density profiles are 185 arcsec and 1000 arcsec respectively. Only about 22 percent of cluster members are present in the core region. The effects of mass segregation, most probably due to dynamical evolution, have been observed in the cluster. The mass function slope of the entire cluster is -0.67 ± 0.12. It becomes closer to the Salpeter value of -1.35, if flattening in the cluster mass function due to presence of both binaries and a much more extended corona is considered.