High‐resolution spectroscopy of ROSAT ‐discovered weak‐line T Tauri stars near Lupus

We present high‐resolution optical echelle spectroscopy for a large fraction of the Li‐rich late‐type stars recently discovered in the vicinity of the Lupus dark clouds. Our results confirm the high Li  i   λ 6708 equivalent widths previously estimated from medium‐resolution spectra, thus adding strength to the conclusion that the large majority of these stars are still in the pre‐main‐sequence phase of their evolution, contrary to claims from other authors that many of them might be zero‐age main‐sequence stars. We present a statistical approach to derive a mean distance for the sample, and find that it is consistent with, or slightly lower than, the Hipparcos distance of the Lupus star‐forming region. The radial velocities measured for part of these stars are consistent with those observed for the Lupus star‐forming region, while stars outside the dark clouds show a mean difference of the order of 3 km s −1 . The projected rotational velocities show a lack of slow rotators, which is interpreted as a consequence of the X‐ray selection of the sample. The Li‐rich stars in Lupus studied in this work yield a fairly ‘clean’ sample of very young stars, while in other star‐forming regions a larger fraction of older zero‐age main‐sequence stars has been found among ROSAT ‐discovered Li‐rich stars. We argue that this fact reflects the relation of these stars with the Gould Belt.