J/ApJ/787/109ivo://CDS.VizieR/J/ApJ/787/109doi:10.26093/cds/vizier.17870109CDSGetman K.V.Feigelson E.D.Kuhn M.A.2017-09-04T08:02:11Z2017-07-06T12:34:06ZCDS support team

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

cds-question@unistra.fropen-star-clustersstellar-agesstellar-distancex-ray-sourcesWe analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age_JX_, derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age_JX_ estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.2014ApJ...787..109Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/787/109CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/582/382 : Chandra X-ray sources in Orion Nebula ClusterJ/ApJ/598/375 : Chandra X-ray observations of NGC 2024 (Skinner+, 2003)J/ApJS/160/319 : COUP: observations and source lists (Getman+, 2005)J/ApJS/160/353 : Membership of the Orion nebula population (Getman+, 2005)J/ApJS/160/450 : X-ray emission in Orion Nebula young stars (Flaccomio+, 2005)J/ApJ/646/1215 : Low-mass stars and brown dwarfs in NGC 2024 (Levine+, 2006)J/ApJ/671/605 : NGC 2264 and ONC PMS stars in the infrared (Cieza+, 2007)J/ApJS/209/27 : MYStIX: the Chandra X-ray sources (Kuhn+, 2013)J/ApJS/209/30 : MYStIX project: Bayesian matching (Naylor+, 2013)J/ApJS/209/31 : The MYStIX IR-Excess Source catalog (MIRES) (Povich+, 2013)J/ApJS/209/32 : Probable young stars in the MYStIX project (Broos+, 2013)J/ApJ/787/107 : Spatial structure of young stellar clusters. I. (Kuhn+, 2014)J/ApJ/787/108 : Age estimates for massive SFR stellar populationshttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/787/109https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/787/109http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/787/109https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/787/109https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/787/109http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/787/109GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/787/109/table1 (Age_JX_ Estimates for NGC 2024 and ONC Stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/787/109/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/787/109/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/787/109/table1?GETtext/xml+votable180.050000true85.32498889-1.824786940.0055555555555555566/21438 21439 22805 22855https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/787/109?format=asciiX-raydefaultJ/ApJ/787/109/table1Age_JX_ Estimates for NGC 2024 and ONC StarsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintCIDCluster identifier (NGC 2024, ONC)meta.id.parentcharMPCMMYStIX source IAU designation (HHMMSS.ss+DDMMSS.s)meta.id;meta.maincharRAJ2000Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainRAngular distance from cluster centerpcpos.angDistancefloatlogLXLog intrinsic 0.5-8 keV X-ray luminosity (1)log(1e-07W)phys.luminosity;em.X-rayfloatAgeAge estimate from Getman et al. 2014ApJ...787..108G (2)Myrtime.agefloatDFlagDisk flag (3)meta.codecharAFlagAnnular region stratum (4)phys.angSizechar