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

TL;DR

This study provides detailed optical and near-infrared photometry of open clusters NGC 637 and NGC 957, determining their physical parameters, stellar content, and dynamical states, including the discovery of a new Be star.

Contribution

It offers new photometric data and analysis of these clusters, including their ages, distances, reddening laws, and the identification of Be stars, enhancing understanding of their properties.

Findings

Both clusters are approximately 10 million years old.

They are located around 2.2-2.5 kpc from Earth.

Both clusters are dynamically relaxed.

Abstract

We present UBVRI CCD photometry in the region of the open clusters NGC 637 and NGC 957. The radii are found to be 4.2 arcmin and 4.3 arcmin. Their reddenings E(B-V) are 0.64+/-0.05 mag and 0.71+/-0.05 mag and their distances, from main sequence fitting are 2.5+/-0.2 kpc 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 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.