Long-term investigation of an open cluster Berkeley 65

TL;DR

This decade-long study of the open cluster Berkeley 65 provides detailed measurements of its physical properties, identifies variable stars, and discusses ongoing disruption effects, contributing valuable data to stellar cluster evolution research.

Contribution

The paper offers the first comprehensive long-term optical investigation of Berkeley 65, including its physical parameters, variable star classification, and evidence of cluster disruption.

Findings

Cluster radius estimated at 1.6 arcminutes

Age determined to be approximately 160 million years

Identification of 64 periodic and 16 non-periodic variable stars

Abstract

We present a decade-long investigation of a poorly studied cluster, Berkeley 65 (Be 65), using deep optical data from the telescopes of ARIES, Nainital Observatory. We estimate its radius ($R_{cluster}$ = 1.6$^{'}$, aspect ratio of $\sim$1.1), distance (2.0 $\pm$ 0.1 kpc) and age ($\sim$160 Myrs). A clear turn-off point at $\sim$1.7 M$_\odot$ in the mass function suggests the escape of low-mass stars, and the lower photometric mass compared to the dynamical mass indicates ongoing disruption due to external forces. Our long-baseline optical photometric data also identifies 64 periodic and 16 non-periodic stars in this region. We have presented the light curves and the classification of those variables. The periodic stars have periods ranging from $\sim$0.05 days to $\sim$3.00 days and amplitude ranges from $\sim$8 mmag to $\sim$700 mmag. The nonperiodic stars show variation from $\sim$30 mmag to $\sim$500 mmag. The periodic stars include main-sequence pulsating variables such as Slow Pulsating B-type, $\delta$ Scuti, RR Lyrae, and $\gamma$ Doradus. We report a detached binary system and rotating variables similar to BY Draconis-type stars exhibiting variable brightness caused by starspots, chromospheric activity, and magnetic field-related phenomena.