A deep XMM-Newton X-ray observation of the Chamaeleon I dark cloud

Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: jrobrade@hs.uni-hamburg.de

Received: 15 August 2006
Accepted: 20 September 2006

Abstract

Context.Low-mass stars are known to exhibit strong X-ray emission during the early stages of evolution. Nearby star forming regions are ideal targets to study the X-ray properties of pre-main sequence stars.

Aims.A deep XMM-Newton exposure is used to investigate X-ray properties of the pre-main sequence population of the Chamaeleon I star forming region.

Methods.The northern-eastern fringe of the Chameleon I dark cloud was observed with XMM-Newton, revisiting a region observed with ROSAT 15 years ago. Centered on the extended X-ray source CHXR 49 we are able to resolve it into three major contributing components and to analyse their spectral properties. Furthermore, the deep exposure allows not only the detection of numerous, previously unknown X-ray sources, but also the investigation of variability and the study of the X-ray properties for the brighter targets in the field. We use EPIC spectra, to determine X-ray brightness, coronal temperatures and emission measures for these sources, compare the properties of classical and weak-line T Tauri stars and make a comparison with results from the ROSAT observation.

Results.X-ray properties of T Tauri stars in Cha I are presented. The XMM-Newton images resolve some previously blended X-ray sources, confirm several possible ones and detect many new X-ray targets, resulting in the most comprehensive list with 71 X-ray sources in the northern Cha I dark cloud. The analysis of medium resolution spectra shows an overlapping distribution of spectral properties for classical and weak-line T Tauri stars, with the X-ray brighter stars having hotter coronae and a higher ratio. X-ray luminosity correlates with bolometric luminosity, whereas the ratio is slightly lower for the classical T Tauri stars. Large flares as well as a low iron and a high neon abundance are found in both types of T Tauri stars. Abundance pattern, plasma temperatures and emission measure distributions during quiescent phases are attributed to a high level of magnetic activity as the dominant source of their X-ray emission.