J/ApJ/899/121ivo://CDS.VizieR/J/ApJ/899/121doi:10.26093/cds/vizier.18990121CDSLim B.Hong J.Yun H.-S.Hwang N.Kim J.S.Lee J.-E.Park B.-G.,Park S.2022-03-15T03:47:36Z2021-11-03T12:22:04ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fropen-star-clustersearly-type-starspre-main-sequence-starsstar-forming-regionsvisible-astronomyspectroscopyradial-velocityproper-motionsStellar kinematics provides the key to understanding the formation process and dynamical evolution of stellar systems. Here, we present a kinematic study of the massive star-forming region (SFR) W4 in the Cassiopeia OB6 association using the Gaia Data Release 2 and high-resolution optical spectra. This SFR is composed of a core cluster (IC1805) and a stellar population distributed over 20pc, which is a typical structural feature found in many OB associations. According to a classical model, this structural feature can be understood in the context of the dynamical evolution of a star cluster. The core-extended structure exhibits internally different kinematic properties. Stars in the core have an almost isotropic motion, and they appear to reach virial equilibrium given their velocity dispersion (0.9{+/-}0.3km/s) comparable to that in a virial state (~0.8km/s). On the other hand, the distributed population shows a clear pattern of radial expansion. From the N-body simulation for the dynamical evolution of a model cluster in subvirial state, we reproduce the observed structure and kinematics of stars. This model cluster experiences collapse for the first 2Myr. Some members begin to radially escape from the cluster after the initial collapse, eventually forming a distributed population. The internal structure and kinematics of the model cluster appear similar to those of W4. Our results support the idea that the stellar population distributed over 20pc in W4 originate from the dynamical evolution of IC1805.2020ApJ...899..121Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/899/121CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)J/AJ/105/499 : OB Associations and Spiral Structure in M33 (Regan+ 1993)J/ApJ/454/151 : OB Associations of the Northern Milky Way (Massey+ 1995)J/AJ/120/333 : UBVRI and H{alpha} in NGC 6530 (Sung+, 2000)J/A+A/371/497 : OB associations in spiral galaxy NGC 300 (Pietrzynski+, 2001)J/AJ/128/805 : Low-mass stars in Cepheus OB2 region (Sicilia-Aguilar+, 2004)J/AJ/134/1368 : Proper motions in NGC 2244 and NGC 6530 (Chen+, 2007)J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)J/A+A/502/1015 : OB associations in IC 1613 (Garcia+, 2009)J/ApJ/726/19 : Intermediate-mass stars in IC 1805 (Wolff+, 2011)J/ApJ/746/15 : Runaway massive stars from R136 (Banerjee+, 2012)J/A+A/537/A146 : Stellar models rotation. 0.8<M<120, Z=0.014 (Ekstrom+, 2012)J/AJ/145/37 : UBVI and H{alpha} CCD photometry of NGC 6231 (Sung+, 2013)J/MNRAS/443/454 : UBVIH{alpha} photometry in NGC 1893 (Lim+, 2014)J/A+A/594/A82 : XMM sources in IC 1805 (Rauw+, 2016)J/ApJS/230/3 : Optical & Spitzer photometry in IC 1805 (Sung+, 2017)J/A+A/618/A93 : Gaia DR2 open clusters in the Milky Way (Cantat-Gaudin+, 2018)J/MNRAS/477/1993 : NGC 1893 stars LSR velocities (Lim+, 2018)J/AJ/157/109 : Stellar proper motions in the Orion Nebula Cluster (Kim+, 2019)J/ApJ/870/32 : Kinematics in young star clusters & associations (Kuhn+, 2019)J/ApJ/884/6 : Known members of Orion A with Gaia DR2 data (McBride+, 2019)J/AJ/157/112 : IR photometry of YSOs in the W4 cloud complex (Panwar+, 2019)J/ApJ/873/66 : Massive stars SDSS/APOGEE-2. II. W3-W4-W5 (Roman-Lopes+, 2019)J/AJ/159/272 : Orion Nebula Cluster PMs HST Treasury Program (Platais+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/899/121https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/899/121http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/899/121https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/899/121https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/899/121http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/899/121GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/899/121/table1 (Catalogue of kinematic members)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/899/121/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/899/121/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/899/121/table1?GETtext/xml+votable180.050000true37.44137561.57836110.0055555555555555566/3307 33101.9867573869263685e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/899/121?format=asciiOpticaldefaultJ/ApJ/899/121/table1Catalogue of kinematic membersSeq[1/127] Sequential numbermeta.id;meta.mainintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDisplay data from gaia DR2 (I/345) within 1"meta.ref.urlintnullableRAJ2000[2] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[61] Degree of Declination (J2000)pos.eq.dec;meta.mainPlx[0.31/0.64] Absolute parallax from Gaia DR2maspos.parallaxfloate_Plx[0.01/0.2] Uncertainty in Plxmasstat.error;pos.parallaxfloatpmRA[-1.1/-0.32] Gaia DR2 Proper motion, in right-ascensionmas/yrpos.pm;pos.eq.rafloate_pmRA[0.02/0.2] Uncertainty in pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatpmDE[-1.4/-0.22] Gaia DR2 proper motion, in declinationmas/yrpos.pm;pos.eq.decfloate_pmDE[0.03/0.229] Uncertainty in pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatGmag[8.28/17.95] Gaia DR2 G band magnitudemagphot.mag;em.optfloate_Gmag[0.0002/0.02] Uncertainty in Gmagmagstat.error;phot.magfloatBPmag[8.55/19.01] Gaia DR2 BP band magnitudemagphot.mag;em.opt.Bfloate_BPmag[0.0007/0.1017] Uncertainty in BBmagmagstat.error;phot.magfloatRPmag[7.88/16.86] Gaia DR2 RB band magnitudemagphot.mag;em.opt.Rfloate_RPmag[0.0005/0.09] Uncertainty in RPmagmagstat.error;phot.magfloatRVel[-117.1/-10.09]? Radial Velocitykm/sphys.veloc;pos.heliocentricdoublenullablee_RVel[0.4/15]? Uncertainty in RVelkm/sstat.error;spect.dopplerVelocfloatnullableBinBinarity flag; SB2 = double-lined spectroscopic binary candidate (2 occurrences)meta.code.multipchar