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2008ApJ...675..464W - Astrophys. J., 675, 464-490 (2008/March-1)

A Chandra study of the Rosette star-forming complex. I. The stellar population and structure of the young open cluster NGC 2244.


Abstract (from CDS):

We present the first high spatial resolution X-ray study of NGC 2244, the 2 Myr old stellar cluster in the Rosette Nebula, using Chandra. Over 900 X-ray sources are detected; 77% have optical or FLAMINGOS NIR stellar counterparts and are mostly previously uncataloged young cluster members. The X-ray-selected population is estimated to be nearly complete between 0.5 and 3 M. A number of further results emerge from our analysis: (1) The X-ray LF and the associated K-band LF indicate a normal Salpeter IMF for NGC 2244. This is inconsistent with the top-heavy IMF reported from earlier optical studies that lacked a good census of <4 Mstars. By comparing the NGC 2244 and Orion Nebula Cluster XLFs, we estimate a total population of ∼2000 stars in NGC 2244. (2) The spatial distribution of X-ray stars is strongly concentrated around the central O5 star, HD 46150. The other early O star, HD 46223, has few companions. The cluster's stellar radial density profile shows two distinctive structures: a power-law cusp around HD 46150 that extends to ∼0.7 pc, surrounded by an isothermal sphere extending out to 4 pc with core radius 1.2 pc. This double structure, combined with the absence of mass segregation, indicates that this 2 Myr old cluster is not in dynamical equilibrium. (3) The fraction of X-ray-selected cluster members with K-band excesses caused by inner protoplanetary disks is 6%, slightly lower than the 10% disk fraction estimated from the FLAMINGOS study based on the NIR-selected sample. (4) X-ray luminosities for 24 stars earlier than B4 confirm the long-standing log(LX/Lbol)~-7 relation. The Rosette OB X-ray spectra are soft and consistent with the standard model of small-scale shocks in the inner wind of a single massive star.

Abstract Copyright:

Journal keyword(s): ISM: Individual: Name: Rosette Nebula - Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 2244 - Stars: Formation - Stars: Luminosity Function, Mass Function - Stars: Pre-Main-Sequence - X-Rays: Stars

VizieR on-line data: <Available at CDS (J/ApJ/675/464): table2.dat table3.dat table4.dat table5.dat table6.dat>

Nomenclature: Table 2: [WTF2008] Main NNN N=805 among (Nos 1-919). Table 3: [WTF2008] Secondary NNN N=114 among (Nos 1-907). Table 6, col(14): [WTF2008] FLAMINGOS JHHMMSS+DDMMSS N=662.

Simbad objects: 978

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