Eric D. Feigelson, Konstantin Getman, Leisa Townsley,
Gordon Garmire, Thomas Preibisch, Nicolas Grosso, Thierry Montmerle,
Augustus Muench, Mark McCaughrean
Global X-ray properties of the Orion Nebula
region
Astrophysical Journal Supplements, COUP Special
Issue, 160, 379-389 (2005)
Abstract.
Based on the Chandra Orion Ultradeep Project (COUP) observation, we
establish the global X-ray properties of the stellar population
associated with the Orion Nebula. Three components contribute roughly
equally to the integrated COUP luminosity in the hard (2-8 keV) X-ray
band: several OB stars, 822 lightly obscured cool stars in the Orion
Nebula Cluster (ONC), and 559 heavily obscured stars. ONC stars 0.5-2
pc from the center show a spatial asymmetry consistent with violent
relaxation in the stellar dynamics. The obscured COUP sources
concentrate around both OMC-1 molecular cores; these small-scale
structures indicate ages t < 0.1 Myr. The X-ray luminosity function
(XLF) of the lightly obscured sample is roughly lognormal in shape. The
obscured population is deficient in lower-luminosity stars, perhaps due
to localized circumstellar material. Mass-stratified XLFs show that
one-third of the Orion Nebula region hard-band emission is produced by
the bright O6 star theta-1 Ori C and half is produced by lower mass
pre-main sequence stars with masses 0.3 < M < 3 Mo. Very low mass
stars contribute little to the cluster X-ray emission.
Using the hard band emission, we show that young stellar clusters like
the ONC can be readily detected and resolved with Chandra across the
Galactic disk, even in the presence of heavy obscuration. The Orion
Nebula sample is a valuable template for studies of distant clusters.
For example, the peak of the XLF shape can serve as a standard candle
for a new distance measure to distant young stellar clusters, and the
presence of a neon emission line complex around 1 keV can serve as a
diagnostic for young stars.
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