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A RAVE investigation on Galactic open clusters: II. Open cluster pairs, groups and complexes

Conrad, C.; Scholz, R.-D.; Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.; De Jong, R. S.; Schnurr, O.; Steinmetz, M.; Grebel, E. K.; Zwitter, T.; Bienaymé, O.; Bland-Hawthorn, J.; Gibson, B. K.; Gilmore, G.; Kordopatis, G.; Kunder, A.; Navarro, J. F.; Parker, Q.; Reid, W.; Seabroke, G.; Siviero, A.; Watson, F.; Wyse, R.


C. Conrad

R.-D. Scholz

N. V. Kharchenko

A. E. Piskunov

S. Röser

E. Schilbach

R. S. De Jong

O. Schnurr

M. Steinmetz

E. K. Grebel

T. Zwitter

O. Bienaymé

J. Bland-Hawthorn

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Professor Brad Gibson
Head of Dept, Physics & Maths; Director, E.A. Milne Centre for Astrophysics

G. Gilmore

G. Kordopatis

A. Kunder

J. F. Navarro

Q. Parker

W. Reid

G. Seabroke

A. Siviero

F. Watson

R. Wyse


© ESO, 2017. 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.


Conrad, C., Scholz, R., Kharchenko, N. V., Piskunov, A. E., Röser, S., Schilbach, E., …Wyse, R. (2017). A RAVE investigation on Galactic open clusters: II. Open cluster pairs, groups and complexes. Astronomy and Astrophysics, 600, A106.

Journal Article Type Article
Acceptance Date Dec 15, 2016
Online Publication Date Apr 7, 2017
Publication Date Apr 1, 2017
Deposit Date Jul 9, 2018
Publicly Available Date Jul 12, 2018
Journal Astronomy and Astrophysics
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 600
Pages A106
Keywords Open clusters and associations: general; Stars: kinematics and dynamics; Galaxy: kinematics and dynamics; Stars: abundances; Solar neighbourhood
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