J/ApJ/787/108 Age estimates for massive SFR stellar populations (Getman+, 2014)
Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer. Getman K.V., Feigelson E.D., Kuhn M.A., Broos P.S., Townsley L.K., Naylor T., Povich M.S., Luhman K.L., Garmire G.P. <Astrophys. J., 787, 108 (2014)> =2014ApJ...787..108G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, ages ; Clusters, open ; X-ray sources ; Morphology ; Photometry, infrared Keywords: infrared: stars - open clusters and associations: general - stars: early-type - stars: formation - stars: pre-main sequence - X-rays: stars Abstract: A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, AgeJX. Stellar masses are derived from X-ray luminosities using the LX-M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. AgeJX is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The AgeJX method has been applied to 5525 out of 31784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The AgeJX ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J-H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters. Description: The 31784 MYStIX Probable Complex Members (MPCMs) constitute the initial stellar sample for this study (Broos et al. 2013, J/ApJS/209/32). The MPCM sample is extracted from source catalogs constructed by special analysis of data from the Chandra X-ray Observatory, Spitzer Space Telescope, United Kingdom InfraRed Telescope, and Two Micron All Sky Survey (2MASS) telescopes. The MPCMs are a union of statistically classified X-ray selected stars, photometric infrared excess stars, and published OB stars. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 103 5525 Individual Stellar Age Estimates table2.dat 75 150 Age Estimates for the MYStIX Clusters
See also: J/ApJS/209/27 : MYStIX: the Chandra X-ray sources (Kuhn+, 2013) J/ApJS/209/28 : MYStIX Wide-Field NIR data: crowded fields (King+, 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/787/109 : Age estimates for NGC 2024 and ONC stars (Getman+, 2014) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Region Star formation region 10- 28 A19 --- Name MYStIX IAU source identifier (HHMMSS.ss+DDMMSS.s) 30- 39 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) 41- 50 F10.6 deg DEdeg Declination in decimal degrees (J2000) 52- 56 F5.2 mag Jmag 2MASS J band magnitude (1) 58- 61 F4.2 mag e_Jmag Uncertainty in Jmag 63- 67 F5.2 mag Hmag 2MASS H band magnitude (1) 69- 72 F4.2 mag e_Hmag Uncertainty in Hmag 74- 78 F5.2 mag Ksmag 2MASS Ks band magnitude (1) 80- 83 F4.2 mag e_Ksmag Uncertainty in Ksmag 85- 88 F4.2 10+23W LX Intrinsic 0.5-8 keV band X-ray luminosity; 1030 erg/s (1) 90- 93 F4.2 10+23W e_LX Uncertainty in LX (2) 95- 97 F3.1 mag AJ J band extinction estimate 99-101 F3.1 Myr AgeJX The AgeJX estimate (3) 103 A1 --- Mem Cluster membership code (G1)
Note (1): From Broos et al. (2013, J/ApJS/209/32). Note (2): The statistical and systematic errors on LX are summed in quadrature. Note (3): Individual age estimates of 5 Myr indicate that ages run into our truncation limit of 5 Myr.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Region Star formation region 10 A1 --- Mem Cluster membership code (G1) 12- 21 F10.6 deg RAdeg ? Right Ascension in decimal degrees (J2000) 23- 32 F10.6 deg DEdeg ? Declination in decimal degrees (J2000) 34- 36 F3.1 arcmin R ? Spatial extent of a MYStIX cluster (1) 38- 41 F4.1 pc Rpc ? Spatial extent of a MYStIX cluster (2) 43- 46 I4 --- Ntot Total number of MYStIX stars assigned as cluster member 48- 50 F3.1 mag Ntotm ? MYStIX stars median J-H color (Kuhn et al. 2014, J/ApJ/787/107) 52- 54 I3 --- NAgeJX ? Number of AgeJX stars assigned as cluster member 56- 58 F3.1 mag NAgeJXm ? AgeJX stars median J-H color 60- 62 F3.1 mag e_NAgeJXm ? Uncertainty in NAgeJXm 64- 66 F3.1 Myr AgeJXm ? Cluster median(AgeJX) estimate 68- 70 F3.1 Myr e_AgeJXm ? Uncertainty in AgeJXm 72- 74 F3.1 Myr AgeJH ? Independent age estimate (3) 75 A1 --- u_AgeJH [:] Uncertainty flag on AgeJH
Note (1): This is 4xcluster core radius in arc-minutes. Note (2): This is 4xcluster core radius in parsecs. Note (3): For the heavily reddened MYStIX clusters, with (J-H)tot>1.5 mag, independent age estimates are given based on the calibration curve of Figure 4.
Global notes: Note (G1): From Kuhn et al. (2014, J/ApJ/787/107). Unclustered or ambiguous stars are denoted as 'U'. All AgeJX members of the W 3, W 4, and NGC 3576 regions are denoted as 'U', since these regions were omitted from the analyses of Kuhn et al. The other letters stand for individual subclusters defined in Kuhn et al. (2014, J/ApJ/787/107). Letters "A"-"T" give the subcluster assignments for particular MYStIX Probable Complex Members (MPCMs). Component name are labeled from east to west.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 29-Jun-2017
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