A Gaia DR2 view of the open cluster population in the Milky Way

Abstract

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the sub-milliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compile a list of thousands of known or putative clusters from the literature. We then apply an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

“…The distance to these clusters are found to be 957±152, 982±132, and 2554±387 pc for the clusters NGC 381, NGC 2360, Be 68, respectively. The derived distances are in agreement with the distances of 1024, 970, and 2437 for the clusters NGC 381, NGC 2360, and Be 68 obtained by Cantat-Gaudin et al (2018). The present estimated age of the cluster NGC 381 is 447±52 Myr which is in close agreement with the age ∼500 Myr obtained by Bossini et al (2019) and slightly higher than ∼320 Myr reported by Ann et al (2002) but is significantly less than 1.1 Gyr reported by Phelps & Janes (1994).…”

“…The tidal Table 1. The values of parameters listed in the Cantat-Gaudin et al (2018) and WEBDA for the clusters in the present study. The values of RA, DEC, l, b, Dist.…”

“…Since most of the OCs are likely to be affected by the field star contamination, the knowledge of membership of the cluster stars is absolutely necessary to investigate the cluster properties E-mail: jayanand@aries.res.in (Carraro et al 2008;Kharchenko et al 2013;Cantat-Gaudin et al 2018). There are many methods to determine the membership of cluster stars using photometric, proper motions, radial velocities, polarimetric data and their combinations (Joshi et al 2012;Medhi & Tamura 2013;Gao 2014).…”

“…Cantat-Gaudin et al (2018) searched members for NGC 381 and NGC 2360 in wider regions of ∼869 and ∼4471 arcmin 2 , respectively in comparison to ∼324 arcmin 2 region in our study. Thus the greater number of member stars found in case of NGC 381 and NGC 2360 can be attributed to larger regions chosen for these clusters byCantat-Gaudin et al (2018). Using our defined cluster members, we estimated the mean proper motion values for the member stars as well as field stars which are given inTable 6.…”

CCD UBV(RI)KC photometry of the open clusters Juchert 9 and Berkeley 97

“…A correction of 0.005 mas to the median values of our original Gaia DR2 parallaxes gives a closer distance with a difference 0.10 kpc (Juc 9) and 0.05 kpc (Be 97). Gaia DR2 parallax Cantat-Gaudin et al (2018) participating in the Gaia Multilateral Agreement. The Gaia mission website is http://www.cosmos.esa.int/gaia.…”