A STUDY OF THE CHAMELEON STAR-FORMING REGION FROM THE ROSAT ALL-SKY SURVEY .3. HIGH-RESOLUTION SPECTROSCOPIC STUDY

We present the results of a high-resolution spectroscopic study on som e 70 stars, discovered recently on the basis of the ROSAT all-sky surv ey spread over a wide area in the Chamaeleon star forming region and c lassified as new weak-line T Tauri stars. We refine the previous spect ral type classification, based on low-resolution spectra, and characte rize each star in the sample according to the Her line profile. We use the strength of Li I 6708, compared to Pleiades stars of the same spe ctral type, as a youth discriminator in order to recognize bona-fide p re-main sequence stars. According to the adopted ''lithium criterion'' , more than 50% of the stars in our sample are confirmed to be truly y oung, PMS stars (most having age less than 5 x 10(6) yr), while the re maining part seems mostly composed by active, young, foreground main-s equence stars (possibly Pleiades-like), which contaminate the original sample. We confirm the existence of some very young stars far from th e main Chamaeleon clouds, while we do not find clear evidence for the presence of post-T Tauri stars in our sample. We find that 5 stars in the sample are spectroscopic binaries and 1 is a spectroscopic triple system. We derive radial and rotational velocities for all the stars i n sample and analyse their distributions for different spectral type i ntervals. The radial velocity distribution shows a clear peak at about 15 km s(-1), which coincides with the radial velocity of stars and ga s in the Cha I cloud. However, the velocity dispersion of the weak-lin e T Tauri stars appears much broader and, possibly, a second peak is p resent around 16-18 km s(-1). A clear segregation in radial velocity i s observed between the strong-lithium and the weak-lithium stars, with the former showing radial velocities which, in most cases, fall in th e interval 12<RV [km/s] < 18, consistent with the radial velocity peak observed for the Cha I dark cloud, and the latter having somewhat dif ferent and more widely spread radial velocities. Some strong-lithium s tars having radial velocities outside the aforementioned interval migh t be unrecognized spectroscopic binaries, but they may also be conside red good candidates to be run-away T Tauri stars. The nu sini distribu tion of the confirmed WTTS is found to resemble very closely that of o ther pre-ROSAT PMS stars. We conclude that the whole star forming regi on has a common origin, possibly related to the impact of a high-veloc ity cloud with the galactic plane.