• DOI:10.1086/340936
• Corpus ID: 17623931

X-Ray-emitting Young Stars in the Orion Nebula

@article{Feigelson2002XRayemittingYS,
  title={X-Ray-emitting Young Stars in the Orion Nebula},
  author={Eric D. Feigelson and Patrick S. Broos and James A. Gaffney III and Gordon P. Garmire and L. A. Hillenbrand and Steven H. Pravdo and Leisa K. Townsley and Yohko Tsuboi},
  journal={The Astrophysical Journal},
  year={2002},
  volume={574},
  pages={258 - 292}
}

• E. Feigelson, P. Broos, +5 authors Y. Tsuboi
• Published 19 March 2002
• Physics
• The Astrophysical Journal

The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a pre-main-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M☉ O star. Source luminosities span 5 orders of magnitude from log LX ≃ 28.0 to 33.3 ergs s-1 in the 0.5-8 keV band, plasma energies range from 0.2 to >10 keV, and absorption ranges from log NH < 20.0 to ~23.5 cm-2. Comprehensive tables providing X-ray and stellar characteristics are provided electronically. We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: (a) the discovery of rapid variability in the O9.5 31 M☉ star θ2A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the "saturation" level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T ≥ 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.