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Issue A&A
Volume 429, Number 3, January III 2005
Page(s) 963 - 975
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20040480



A&A 429, 963-975 (2005)
DOI: 10.1051/0004-6361:20040480

The X-ray emission from Young Stellar Objects in the $\rho$ Ophiuchi cloud core as seen by XMM-Newton

H. Ozawa, N. Grosso and T. Montmerle

Laboratoire d'Astrophysique de Grenoble, Université Joseph-Fourier, 38041 Grenoble Cedex 9, France

(Received 19 March 2004 / Accepted 29 June 2004)

Abstract
We observed the main core F of the $\rho$ Ophiuchi cloud, an active star-forming region located at $d \sim 140$ pc, using XMM-Newton with an exposure of 33 ks. We detect 87 X-ray sources within the 30 $\arcmin$ diameter field-of-view of the EPIC imaging detector array. We cross-correlate the positions of XMM-Newton X-ray sources with previous X-ray, infrared (IR), and optical catalogs: 25 previously unknown X-ray sources are found from our observation; 43 X-ray sources are detected by both XMM-Newton and Chandra; 68 XMM-Newton X-ray sources have 2MASS near-IR counterparts. We show that XMM-Newton and Chandra have comparable sensitivity for point source detection when the exposure time is set to ~30 ks for both. We detect X-ray emission from 7 Class I sources, 26 Class II sources, and 17 Class III sources. The X-ray detection rate of Class I sources is very high (64%), which is consistent with previous Chandra observations in this area. We propose that 15 X-ray sources are new class III candidates, which doubles the number of known Class III sources, and helps to complete the census of YSOs in this area. We also detect X-ray emission from two young bona fide brown dwarfs, GY310 and GY141, out of three known in the field of view. GY141 appears brighter by nearly two orders of magnitude than in the Chandra observation. We extract X-ray light curves and spectra from these YSOs, and find some of them showed weak X-ray flares. We observed an X-ray flare from the bona fide brown dwarf GY310. We find as in the previous Chandra observation of this region that Class I sources tend to have higher temperatures and heavier X-ray absorptions than Class II and III sources.


Key words: Galaxy: open clusters and associations: individual: $\rho$ Ophiuchi cloud -- stars: pre-main sequence -- stars: low-mass, brown dwarfs -- X-rays: stars -- infrared: stars

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© ESO 2005


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