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)
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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