Results from DROXO

III. Observation, source list, and X-ray properties of sources detected in the “Deep Rho Ophiuchi XMM-Newton Observation”

¹ DSFA, Università degli Studi di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: pilli@astropa.unipa.it
² INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
³ SAO-Harvard Center for Astrophysics, Cambridge MA, USA
⁴ ESO – Karl-Scharzschild-Strasse 2, 85748 Garching bei München, Germany
⁵ Laboratoire d'Astrophysique de Grenoble Université Joseph-Fourier, Grenoble, France
⁶ Université de Strasbourg, Observatoire Astronomique de Strasbourg, 11 rue de l'université, 67000 Strasbourg, France
⁷ CNRS, UMR 7550, 11 rue de l'université, 67000 Strasbourg, France
⁸ ESA – Planning and Community Coordination Office, Science Programme, Paris, France
⁹ Astrophysics Division - RSSD ESA, ESTEC, Noordwijk, The Netherlands

Received: 18 February 2009
Accepted: 26 April 2010

Abstract

Context. X-rays from very young stars are powerful probes to investigate the mechanisms at work in the very first stages of the star formation and the origin of X-ray emission in very young stars.

Aims. We present results from a 500 ks long observation of the Rho Ophiuchi cloud with a XMM-Newton large program named DROXO, aiming at studying the X-ray emission of deeply embedded young stellar objects (YSOs).

Methods. The data acquired during the DROXO program were reduced with SAS software, and filtered in time and energy to improve the signal to noise of detected sources; light curves and spectra were obtained.

Results. We detected 111 sources, 61 of them associated with ρ Ophiuchi YSOs as identified from infrared observations with ISOCAM. Specifically, we detected 9 out of 11 Class I objects, 31 out of 48 Class II and 15 out 16 Class III objects. Six objects out of 21 classified Class III candidates are also detected. At the same time we suggest that 15 Class III candidates that remain undetected at logL_x [erg/s] < 28.3 are not related to the cloud population. The global detection rate is ~64%. We have achieved a flux sensitivity of ~5 × 10^-15 erg s^-1 cm^-2. The to ratio shows saturation at a value of ~-3.5 for stars with ≤ 5000 K or 0.7  as observed in the Orion Nebula. The plasma temperatures and the spectrum absorption show a decline with YSO class, with Class I YSOs being hotter and more absorbed than Class II and III YSOs. In one star (GY 266) with infrared counterpart in 2MASS and Spitzer catalogs we have detected a soft excess in the X-ray spectrum, which is best fitted by a cold thermal component less absorbed than the main thermal component of the plasma. This soft component hints at plasma heated by shocks due to jets outside the dense circumstellar material.