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

Abstract

Relative proper motions (PMs) and cluster membership probabilities (P_μ) 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 ∼4 mas 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 P_μ > 70 per cent. A mass function slope of x = 1.60 ± 0.10 was derived for the cluster, and the cluster was found to be dynamically relaxed. Finally, we provide positions, calibrated B and V magnitudes, relative PMs and membership probabilities for the stars in the field of NGC 3766. We have produced a catalogue that is electronically available to the astronomical community.