A RAVE investigation on Galactic open clusters
II. Open cluster pairs, groups and complexes⋆
1 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
2 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12−14, 69120 Heidelberg, Germany
3 Main Astronomical Observatory, 27 Academica Zabolotnogo Str., 03680 Kiev, Ukraine
4 Russian Academy of Science, Institute of Astronomy, 48 Pyatnitskaya, 109017 Moscow, Russia
5 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
6 Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
7 Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia
8 Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, Hull, HU6 7RX, UK
9 Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK
10 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2, Canada
11 Department of Physics, Laboratory for Space Research, University of Hong Kong, Cyberport 4, 100 Cyberport Rd, Telegraph Bay, Hong Kong, PR China
12 Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
13 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
14 Dipartimento di Fisica e Astronomia Galileo Galilei, Universita’ di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
15 Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
16 Johns Hopkins University, Dept of Physics and Astronomy, Baltimore, MD 21218, USA
Received: 4 November 2016
Accepted: 15 December 2016
Context. It is generally agreed upon that stars form in open clusters (OCs) and stellar associations, but little is known about structures in the Galactic OC population; whether OCs and stellar associations are born isolated or if they prefer to form in groups, for example. Answering this question provides new insight into star and cluster formation, along with a better understanding of Galactic structures.
Aims. In the past decade, studies of OC groupings have either been based solely on spatial criteria or have also included tangential velocities for identifications. In contrast to previous approaches, we assumed that real OC groupings occupy a well defined area in the sky and show similar velocity vectors. For the first time, we have used 6D phase-space information, including radial velocities from the RAdial Velocity Experiment (RAVE) and other catalogues, for the detection of OC groupings. We also checked the age spread of potential candidates to distinguish between genuine groupings and chance alignments.
Methods. We explored the Catalogue of Open Cluster Data (COCD) and determined 6D phase-space information for 432 out of 650 listed OCs and compact associations. The group identification was performed using an adapted version of the Friends-of-Friends algorithm, as used in cosmology, with linking lengths of 100 pc and 10–20 km s-1. For the verification of the identified structures, we applied Monte Carlo simulations with randomised samples.
Results. For the linking lengths 100 pc and 10 km s-1 , we detected 19 groupings, including 14 pairs, 4 groups with 3−5 members, and 1 complex with 15 members. The Monte Carlo simulations revealed that, in particular, the complex is most likely genuine, whereas pairs are more likely chance alignments. A closer look at the age spread of the complex and the comparison between spatial distributions of young and old cluster populations suggested that OC groupings likely originated from a common molecular cloud.
Key words: open clusters and associations: general / stars: kinematics and dynamics / Galaxy: kinematics and dynamics / stars: abundances / solar neighborhood
Tables A.1, A.2, and B.1 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A106
© ESO, 2017