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J/ApJ/787/109       Age estimates for NGC 2024 and ONC stars     (Getman+, 2014)

Core-halo age gradients and star formation in the Orion nebula and NGC 2024 young stellar clusters. Getman K.V., Feigelson E.D., Kuhn M.A. <Astrophys. J., 787, 109 (2014)> =2014ApJ...787..109G (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, ages ; Stars, distances ; X-ray sources Keywords: stars: early-type - stars: formation - stars: pre-main sequence Abstract: We 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, AgeJX, 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 AgeJX 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. Description: The MYStIX project has produced rich stellar samples of 31784 probable members of 20 OB-dominated young star-forming regions at distances 0.4-3.6 kpc using sensitive X-ray, NIR, and mid-infrared photometric catalogs (Feigelson et al. 2013, J/ApJS/209/26). Based on the MYStIX data, G14 developed a new PMS stellar age estimator, AgeJX. This estimator is based on J-band stellar photospheric emission and on X-ray emission from coronal magnetic flaring, and relies on an assumption of a nearly universal LX-M relationship for ~<5 Myr old PMS stars (Section 3.1 in G14). Objects: ---------------------------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------------------------- 05 35 17.3 -05 23 28 Orion Nebula cluster = M 42 05 41 43 -01 50.5 NGC 2024 = [BDB2003] G206.47-16.32 ---------------------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 76 512 AgeJX Estimates for NGC 2024 and ONC Stars
See also: J/ApJ/582/382 : Chandra X-ray sources in Orion Nebula Cluster (Flaccomio+, 2003) J/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 populations (Getman+, 2014) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 8 A8 --- CID Cluster identifier (NGC 2024, ONC) 10- 27 A18 --- MPCM MYStIX source IAU designation (HHMMSS.ss+DDMMSS.s) 29- 37 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000) 39- 47 F9.6 deg DEdeg Declination in decimal degrees (J2000) 49- 52 F4.2 pc R Angular distance from cluster center 54- 58 F5.2 [10-7W] logLX Log intrinsic 0.5-8 keV X-ray luminosity (1) 60- 62 F3.1 Myr Age Age estimate from Getman et al. 2014ApJ...787..108G (2) 64- 67 A4 --- DFlag Disk flag (3) 69- 76 A8 --- AFlag Annular region stratum (4)
Note (1): In units of erg/s and from Broos et al. (2013, J/ApJS/209/32). Note (2): Individual age estimates of 5 Myr indicate that ages run into the truncation limit of 5 Myr (Getman et al. 2014ApJ...787..108G). Note (3): For NGC 2024: 'DSK' and 'NOD' - disk-bearing and disk-free young stellar objects; the classification is adopted from the MIRES catalog of Povich et al. (2013, J/ApJS/209/31) based on NIR and Spitzer IRAC photometry. For ONC: 'Ks' and 'noKs' - PMS stars with and without Ks-excess (Section 3.4); the classification is adopted from Getman et al. (2005, J/ApJS/160/319) based on NIR photometry. Note (4): In units of core radii from Figure 1.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 29-Jun-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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