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Issue A&A
Volume 370, Number 1, April IV 2001
Page(s) L22 - L25
Section Letters
DOI 10.1051/0004-6361:20010325



A&A 370, L22-L25 (2001)
DOI: 10.1051/0004-6361:20010325

ROSAT-HRI detection of the Class I protostar YLW16A in the $\mathsf{\rho}$ Ophiuchi dark cloud

N. Grosso

Max-Planck-Institut für extraterrestrische Physik, PO Box 1312, 85741 Garching bei München, Germany

(Received 17 January 2001 / Accepted 2 March 2001)

Abstract
I analyze unpublished or partially published archival ROSAT data of the $\rho$ Ophiuchi dark cloud. This set of seven overlapping ROSAT HRI pointings, composed of eight ~one-hour exposures, detects mainly the X-ray brightest T Tauri stars of this star-forming region. Only two HRI sources are new X-ray sources, and their optical counterparts are proposed as new Weak T Tauri star candidates. Meanwhile the ROSAT HRI caught during just one exposure a weak X-ray source ( ${\cal L}=10$; $SNR=4.1 \sigma$ for Gaussian statistics) among a group of three embedded young stellar objects including two Class I protostars. Previous ROSAT PSPC, ASCA GIS observations, and as I argue here one Einstein IPC observation, have already detected an X-ray source in this area, but this higher angular resolution data show clearly that X-rays are emitted by the Class I protostar YLW16A. This is the second Class I protostar detected by the ROSAT HRI in this dark cloud. The determination of the intrinsic X-ray luminosity of this event, $L_{\rm X}{\rm [0.1{-}2.4 keV]}=(9.4$ erg s-1, critically depends on the source absorption estimate. Improvements will be obtained only by the direct determination of this parameter from fitting of Chandra and XMM-Newton spectra.


Key words: open clusters and association: $\rho$ Oph -- stars: pre-main sequence -- X-rays: stars -- infrared: stars

Offprint request: N. Grosso, ngrosso@xray.mpe.mpg.de

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