Cygnus OB2 DANCe: A high-precision proper motion study of the Cygnus OB2 association

被引:70
作者
Wright, Nicholas J. [1 ,2 ]
Bouy, Herve [3 ]
Drew, Janet E. [2 ]
Manuel Sarro, Luis [4 ]
Bertin, Emmanuel [5 ,6 ]
Cuillandre, Jean-Charles [7 ]
Barrado, David [3 ]
机构
[1] Keele Univ, Astrophys Grp, Keele ST5 5BG, Staffs, England
[2] Univ Hertfordshire, Ctr Astrophys Res, Hatfield AL10 9AB, Herts, England
[3] INTA CSIC, Ctr Astrobiol, Dept Astrofis, POB 78,28691,ESAC Campus, E-208691 Madrid, Spain
[4] UNED, Dept Inteligencia Artificial, Juan del Rosal 16, E-28040 Madrid, Spain
[5] CNRS, UMR 7095, Inst Astrophys Paris, 98bis Bd Arago, F-75014 Paris, France
[6] UPMC, 98bis Bd Arago, F-75014 Paris, France
[7] PSL Res Univ, Observ Paris, Univ Paris Diderot, CEA,IRFU,SAp,Lab AIM Paris Saclay,CNRS,INSU, F-91191 Gif Sur Yvette, France
关键词
stars: early-type; stars: kinematics and dynamics; stars: pre-main-sequence; open clusters and associations: individual: Cygnus OB2; EARLY DYNAMICAL EVOLUTION; STAR-FORMING REGIONS; ORION NEBULA CLUSTER; X-RAY; MASSIVE STARS; KINEMATIC STRUCTURE; INITIAL CONDITIONS; GAS EXPULSION; SKY SURVEY; CYG-OB2;
D O I
10.1093/mnras/stw1148
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present a high-precision proper motion study of 873 X-ray and spectroscopically selected stars in the massive OB association Cygnus OB2 as part of the DANCe project. These were calculated from images spanning a 15 yr baseline and have typical precisions < 1 mas yr(-1). We calculate the velocity dispersion in the two axes to be (c) = 13.0(-0.7)(+0.8) sigma delta(c) = 9.1(-0.5)(+0.5) km s(-1), using a two-component, two-dimensional model that takes into account the uncertainties on the measurements. This gives a three-dimensional velocity dispersion of sigma(3D) = 17.8 +/- 0.6 km s(-1) implying a virial mass significantly larger than the observed stellar mass, confirming that the association is gravitationally unbound. The association appears to be dynamically unevolved, as evidenced by considerable kinematic substructure, non-isotropic velocity dispersions and a lack of energy equipartition. The proper motions show no evidence for a global expansion pattern, with approximately the same amount of kinetic energy in expansion as there is in contraction, which argues against the association being an expanded star cluster disrupted by process such as residual gas expulsion or tidal heating. The kinematic substructures, which appear to be close to virial equilibrium and have typical masses of 40-400 M-aS (TM), also do not appear to have been affected by the expulsion of the residual gas. We conclude that Cyg OB2 was most likely born highly substructured and globally unbound, with the individual subgroups born in (or close to) virial equilibrium, and that the OB association has not experienced significant dynamical evolution since then.
引用
收藏
页码:2593 / 2610
页数:18
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