J/MNRAS/460/2593 Cygnus OB2 DANCe: Proper motion study (Wright+, 2016) ================================================================================ Cygnus OB2 Dance: A high precision proper motion study of the Cygnus OB2 association. Wright N.J., Bouy H., Drew J.E., Sarro L.M., Bertin E., Cuillandre J.-C., Barrado D. =2016MNRAS.460.2593W (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Associations, stellar ; Proper motions Keywords: proper motions - open clusters and associations: individual: Cygnus OB2 Abstract: 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-year baseline and have typical precisions <1mas/yr. We calculate the velocity dispersion in the two axes to be 13.0^+0.8^_-0.7_ and 9.1^+0.5^_-0.5_km/s, using a 2-component, 2-dimensional model that takes into account the uncertainties on the measurements. This gives a 3-dimensional velocity dispersion of 17.8+/-0.6km/s 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 40-400M_{sun}_, 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. Description: Positions, proper motions and source IDs for 873 members of the Cygnus OB2 association. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 83 873 Source positions, proper motions and source IDS -------------------------------------------------------------------------------- See also: J/ApJ/643/238 : Chandra/2MASS sources in Cygnus OB2 (Butt+, 2006) J/A+A/474/495 : X-ray flares from Cygnus OB2 young stars (Albacete Colombo+, 2008) J/A+A/464/211 : Chandra and near-IR obs. of Cyg OB2 (Albacete Colombo+, 2007) J/A+A/472/557 : Cygnus OB2 region 610MHz sources (Marti+, 2007) J/A+A/486/453 : NIR photometry of early-type stars in Cyg OB2 (Comeron+ 2008) J/ApJS/184/84 : X-ray sources in Cyg OB2 region (Wright+, 2009) J/A+A/543/A101 : OB stars in Cygnus OB2 association (Comeron+, 2012) J/ApJ/713/871 : Sources in star-forming region Cyg-OB2 from X-ray (Wright+, 2012) J/MNRAS/449/741 : The massive star population of Cygnus OB2 (Wright+, 2015) J/A+A/575/A120 : DANCe study of M35 (NGC 2168) (Bouy+, 2015) J/A+A/577/A148 : The Seven Sisters DANCe. I. Pleiades (Bouy+, 2015) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 19 A19 --- DANCe DANCe Survey ID (JHHMMSS.ss+DDMMSS.s) 21- 22 I2 h RAh Right ascension (J2000.0) 24- 25 I2 min RAm Right ascension (J2000.0) 27- 31 F5.2 s RAs Right ascension (J2000.0) 33 A1 --- DE- Declination sign (J2000) 34- 35 I2 deg DEd Declination (J2000.0) 37- 38 I2 arcmin DEm Declination (J2000.0) 40- 43 F4.1 arcsec DEs Declination (J2000.0) 45- 51 F7.2 mas/yr pmRA Proper motion along RA, pmRA*cos(DE) 53- 57 F5.2 mas/yr e_pmRA rms uncertainty on pmRA 59- 65 F7.2 mas/yr pmDE Proper motion along DE 67- 71 F5.2 mas/yr e_pmDE rms uncertainty on pmDE 73- 76 A4 --- IDX X-ray source ID from Wright et al., 2009, Cat. J/ApJS/184/84 ([WD2009] NNNN in Simbad) 78- 80 A3 --- IDMT91 OB star source ID from Massey & Thompson, 1991, Cat. J/AJ/101/1408 ([MT91] NNN in Simbad) 82- 83 A2 --- IDS58 OB star source ID on the Schulte system (1) -------------------------------------------------------------------------------- Note (1): See Johnson & Morgan (1954ApJ...119..344J), Schulte NNA in Simbad. -------------------------------------------------------------------------------- Acknowledgements: Nicholas J. Wright, nick.nwright(at)gmail.com ================================================================================ (End) Nicholas Wright [Keele, UK], Patricia Vannier [CDS] 06-Sep-2016