X-ray emission from T Tauri stars in the Lupus 3 star-forming region
European Space Agency, ESTEC – Postbus 299, 2200 AG Noordwijk, The Netherlands e-mail: email@example.com
Accepted: 15 March 2006
Aims.In this paper, I present analysis results of an observation of the Lupus 3 region that contains a high proportion of young low mass ( 0.3 ) 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 Science Analysis Software. The detected sources were correlated with a list of Herbig-Haro objects and H 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 1028 to 3 1030 erg s-1. Two of these objects with mass estimates lower than 0.075 have an X-ray luminosity of about 4–7 1028 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 3–9 106 K and 1–50 107 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 1052 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.
Key words: stars: activity / stars: atmospheres / stars: coronae / stars: evolution / stars: low-mass, brown dwarfs - stars: late-type
© ESO, 2006