1 Introduction

It has long been known that in the solar vicinity there are several kinematic groups of stars that share the space motions of well-known open clusters. Eggen (1994) defined a "supercluster'' (SC) as a group of stars, gravitationally unbound, that share the same kinematics and may occupy extended regions in the Galaxy, and a "moving group'' (MG) as the part of the supercluster that enters the solar neighbourhood and can be observed all over the sky. The origin of these stellar kinematic groups (SKG) could be the evaporation of an open cluster, the remnants of a star formation region or a juxtaposition of several little star formation bursts at different epochs in adjacent cells of the velocity field. The youngest and best-documented SKG are: the Hyades supercluster (600 Myr) the Ursa Major group (Sirius supercluster) (300 Myr), the Local Association or Pleiades moving group (20 to 150 Myr), the IC 2391 supercluster (35-55 Myr), and the Castor moving group (200 Myr) (see Montes et al. 2001b, hereafter Paper I, and references therein).

Well-known members of these SKG are mainly early-type stars and few studies have been centered on late-type stars. However, the identification of a significant number of late-type population in these young SKG is extremely important for the study of the chromospheric activity and could lead to a better understanding of star formation history in the solar neighbourhood. In our previous work (Montes et al. 2000a, 2001a; Paper I) a sample of late-type stars of previously established members and possible new candidates to these five young SKG have been identified. In order to better establish the membership of these candidate stars in the different young SKG, we have started a program of high resolution echelle spectroscopic observations. The spectroscopic analysis of these stars allows us to obtain a better determination of their radial velocity, lithium ($\lambda$6707.8 line) equivalent width, rotational velocity and the level of chromospheric activity. We will use all these new data to study in detail the kinematics (Galactic space motions (U, V, W)) of these stars, apply age-dating methods for late-type stars, and in this way analyse in more detail the membership of these stars in the different SKG.

We present here the results of our first spectroscopy studies of a sample of 14 single late-type stars selected by us in Paper I as young disk stars or possible members of some of the above mentioned young SKG. The high resolution echelle spectra analysed here were taken during three observing runs (from 1999 to 2000) and include all the optical chromospheric activity indicators from the Ca  II H & K to Ca  II IRT lines as well as the Li  I $\lambda$6707.8 line.

In Sect. 2 we give the details of our observations and data reduction. The radial velocity and Galactic space-velocity components (U, V, W) determination is described in Sect. 3. The Li  I $\lambda$6707.8 line is analysed in Sect. 4. The different chromospheric activity indicators are analysed in Sect. 5. Individual results for each star are reported in Sect. 6. Finally, in Sect. 7 the discussion and conclusions are given.

Figure 1: (U, V) and (W, V) planes (Boettlinger Diagram) for our star sample. We plot with different symbols the stars belonging to the different stellar kinematic groups. Filled symbols are stars that satisfied both of Eggen's criteria (peculiar velocity, PV, and radial velocity, $\rho _{\rm c}$), open symbols are other possible members. Big crosses are plotted in the central position of each group. The dashed line represents the boundaries that determine the young disk population as defined by Eggen (1984a, 1989).