Proper motions and membership probabilities of stars in the region of open cluster NGC 3766

Abstract

Relative proper motions (PMs) and cluster membership probabilities (Pμ) were derived for ~2500 stars in the field of the open star cluster NGC 3766. The cluster was observed in the B and V broad-band filters at two epochs separated by ~6 yr using a wide-field imager mounted on the WFI@ESO 2.2-m telescope. All CCD frames were reduced using the astrometric techniques described by Anderson et al. The PM rms error for stars brighter than V~15 mag is 2.0 mas yr⁻¹, but it gradually increases up to ~4mas yr⁻¹ at V ~ 20 mag. Using PM data, membership probabilities were derived for the stars in the region of the cluster. They indicate that one Ap and three Be stars are members of the cluster. A reddening of E(B − V) = 0.22±0.05 mag, a distance of 2.5 ± 0.5 kpc and an age of ~20 Myr were derived using stars with Pμ >70 per cent.Amass function slope of x=1.60±0.10was derived for the cluster, and the clusterwas found to be dynamically relaxed. Finally,we provide positions, calibrated B and V magnitudes, relative PMsand membership probabilities for the stars in the field ofNGC3766. We have produced a catalogue that is electronically available to the astronomical community.