Optical and near-infrared photometric study of the open cluster NGC 637 and 957

Abstract

We present UBVRI CCD photometry in the region of the open clusters NGC 637 and 957. The radii are found to be 4.2 and 4.3 arcmin. Their reddenings E(B − V) are 0.64 ± 0.05 and 0.71 ± 0.05 mag and their distances, from main-sequence fitting are 2.5 ± 0.2 and 2.2 ± 0.2 kpc. Comparison with Z = 0.02 isochrones leads to an age of 10 ± 5 Myr for both clusters. Combining our photometry with Two Micron All Sky Survey (2MASS) JHK shows the reddening law in these directions to be normal. Mass function slopes of x = 1.65 ± 0.20 and 1.31 ± 0.50 are derived for the clusters, both of which are found to be dynamically relaxed. Spectral and photometric characteristics of three Be stars, two in NGC 957 and one (newly discovered) in NGC 637, indicate them to be of Classical Be type.