UOCS – III. UVIT catalogue of open clusters with machine learning-based membership using Gaia EDR3 astrometry

Abstract

We present a study of six open clusters (Berkeley 67, King 2, NGC 2420, NGC 2477, NGC 2682, and NGC 6940), using the Ultra Violet Imaging Telescope (UVIT) aboard ASTROSAT and Gaia EDR3. We used combinations of astrometric, photometric, and systematic parameters to train and supervise a machine-learning algorithm along with a Gaussian mixture model for the determination of cluster membership. This technique is robust, reproducible, and versatile in various cluster environments. In this study, the Gaia EDR3 membership catalogues are provided along with classification of the stars as members, candidates, and field in the six clusters. We could detect 200–2500 additional members using our method with respect to previous studies, which helped estimate mean space velocities, distances, number of members and core radii. UVIT photometric catalogues, which include blue stragglers, main-sequence, and red giants are also provided. From UV–Optical colour–magnitude diagrams, we found that majority of the sources in NGC 2682 and a few in NGC 2420, NGC 2477, and NGC 6940 showed excess UV flux. NGC 2682 images have 10 white dwarf detection in far-UV. The far-UV and near-UV images of the massive cluster NGC 2477 have 92 and 576 members, respectively, which will be useful to study the UV properties of stars in the extended turn-off and in various evolutionary stages from main sequence to red clump. Future studies will carry out panchromatic and spectroscopic analysis of noteworthy members detected in this study.