X-Ray Emission from Orion Nebula Cluster Stars with Circumstellar Disks and Jets

Joel H. Kastner, Rochester Institute of Technology
Geoffrey Franz, Rochester Institute of Technology
Nicolas Grosso, Universite Joseph-Fourier
John Bally, University of Colorado
Mark J. McCaughrean, Astrophysikalisches Institut Postdam
Konstantin Getman, The Pennsylvania State University
Eric D. Feigelson, The Pennsylvania State University
Norbert S. Schulz, Massachusetts Institute of Technology

© 2005 The American Astronomical Society

COUP is supported by Chandra Guest Observer grant SAO GO3-4009A (E. D. Feigelson, PI) as well as by the Chandra ACIS Team contract NAS8-38252. Additional support for the work described in this paper was provided by Chandra Guest Observer grant GO4-5012X to RIT.

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We investigate the X-ray and near-infrared emission properties of a sample of pre-main sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for circumstellar disks (“proplyds”) and optical jets in Hubble Space Telescope (HST) imaging. Our study uses X-ray data acquired during Chandra Orion Ultradeep Program (COUP) observations, as well as complementary optical and near-infrared data recently acquired with HST and the Very Large Telescope (VLT), respectively. Approximately 70% of ~140 proplyds were detected as X-ray sources in the 838 ks COUP observation of the ONC, including ~25% of proplyds that do not display central stars in HST imaging. In nearinfrared imaging, the detection rate of proplyd central stars is > 90%. Many proplyds display near-infrared excesses, suggesting disk accretion is ongoing onto the central, PMS stars. About 50% of circumstellar disks that are detected in absorption in HST imaging contain X-ray sources. For these sources, we find that X-ray absorbing column and apparent disk inclination are well correlated, providing insight into the disk scale heights and metal abundances of UV- and X-ray-irradiated protoplanetary disks. Approximately 2/3 of the ~30 proplyds and PMS stars exhibiting jets in Hubble images have COUP X-ray counterparts. These jet sources display some of the largest near-infrared excesses among the proplyds, suggesting that the origin of the jets is closely related to ongoing, PMS stellar accretion. One morphologically complex jet source, d181–825, displays a double-peaked X-ray spectral energy distribution with a prominent soft component that is indicative of strong shocks in the jet collimation region. A handful of similar objects also display X-ray spectra that are suggestive of shocks near the jet source. These results support models in which circumstellar disks collimate and/or launch jets from young stellar objects and, furthermore, demonstrate that star-disk-jet interactions may contribute to PMS X-ray emission (Refer to PDF file for exact formulas).