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Published September 2000 | Submitted + Published
Journal Article Open

Chandra X-Ray Observatory Study of the Orion Nebula Cluster and BN/KL Region


About 1000 X-ray emitting young pre–main-sequence (PMS) stars distributed in mass from ~0.05 M☉ brown dwarfs to a ~50 M☉ O star are detected in an image of the Orion Nebula obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is the richest field of sources ever obtained in X-ray astronomy. Individual X-ray luminosities in the Orion Nebula cluster range from the sensitivity limit of 2 × 10^(28) ergs s^(-1) to ~10^(32) ergs s^(-1). ACIS sources include 85%–90% of V < 20 stars, plus a lower but substantial fraction of deeply embedded stars with extinctions as high as A_V ≃ 60. The relationships between X-ray and other PMS stellar properties suggest that X-ray luminosity of lower-mass PMS stars depends more on mass, and possibly stellar rotation, than on bolometric luminosity, as widely reported. In a subsample of 17 unabsorbed stars with mass ≃ 1 M☉, X-ray luminosities are constant at a high level around L_x ≃ 2 × 10^(30) ergs s^(-1) for the first ≃ 2 Myr while descending the convective Hayashi track, but diverge during the 2–10 Myr phase with X-ray emission plummeting in some stars but remaining high in others. This behavior is consistent with the distribution of X-ray luminosities on the zero-age main sequence and with current theories of their rotational history and magnetic dynamos. The sources in the Becklin-Neugebauer/Kleinman-Low region of massive star formation are discussed in detail. They include both unabsorbed and embedded low-mass members of the Orion Nebula cluster, the luminous infrared Source n, and a class of sources without optical or infrared counterparts that may be new magnetically active embedded PMS stars. Several X-ray sources are also variable radio emitters, an association often seen in magnetically active PMS stars. Faint X-ray emission is seen close to, but apparently not coincident with, the Becklin-Neugebauer object. Its nature is not clear.

Additional Information

© 2000 The American Astronomical Society. Received 2000 March 27; accepted 2000 May 30. We express our appreciation of the many scientists and engineers who brought Chandra to fruition, in particular those at MIT, Penn State, and Lockheed-Martin who contributed to the ACIS instrument. Ann Hornschemeier (Penn State), Karl Menten (MPI-Radioastronomie), and John Bally (Colorado) kindly provided results prior to publication, and the referee Ralph Neuhäuser gave many useful comments. This research was funded by NASA contract NAS 8-38252 at Penn State. The contributions of S. H. P. were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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Published - Garmire_2000_AJ_120_1426.pdf

Submitted - 0006087.pdf


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August 19, 2023
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