X-ray emission from T Tauri stars in the Lupus 3 star-forming region

Aims. In this paper, I present analysis results of an XMM-Newton observation of the Lupus 3 region that contains a high proportion of young low mass (M < 0.3 M-circle dot) T Tauri stars in the Lupus star-forming complex. Methods: The detection of X-ray sources in 0.5 to 4.5 keV images of the Lupus 3 core was performed using the standard source detection method of the XMM-Newton Science Analysis Software. The detected sources were correlated with a list of Herbig-Haro objects and Ha emission stars that contains mainly classical T Tauri stars, with a catalogue of weak-line T Tauri Stars and with a recent list of new low-mass members of the Lupus 3 dark cloud found in a visible-light spectroscopic survey at the center of the Lupus 3 star-forming core. The light curves and spectra of the brightest X-ray sources with known T Tauri star counterparts were analysed. Results. One hundred and two X-ray sources were detected in the 30' diameter field-of-view of the EPIC cameras, of which 25 have visible or near-IR counterparts that are known as pre-main sequence stars. Their X-ray luminosity ranges from 3 x 1028 to 3 x 10(30) erg s(-1). Two of these objects with mass estimates lower than 0.075 M-circle dot have an X-ray luminosity of about 4-7 x 10(28) erg s(-1), comparable with that of flaring young brown dwarfs. A linear correlation is found between the X-ray luminosity and the mass or volume of the stars that is qualitatively expected from some models of distributed turbulent dynamos. The EPIC spectra of the X-ray brightest sources can be fitted using optically thin plasma emission models with two components at temperatures in the ranges 3-9 x 10(6) K and 1-50 x 10(7) K, respectively. The large emission measure of hot plasma may be caused by disruptions of magnetic fields associated with an intense flaring activity, while the X-ray emission from the "cool" plasma components may result from solar-type active regions. The emission measures of the plasma components are of the order of 10(52) cm(-3), typical of the values expected from coronal plasmas in T Tauri stars, post-T Tauri stars, and active late-type dwarfs in close binary systems. One property of the X-ray brightest stars in Lupus 3 that seems common among pre-main sequence stars is the low abundance of Fe.