Table 1: Target stars. Columns: name - star name; l, b - Galactic coordinates (from SIMBAD); , - trigonometric parallax and its error (Hipparcos); K, - the equivalent width of the Ca II K line and its error; H, - the equivalent width of the Ca II H line and its error; , - Ca II column density and its error; as, as ref: association membership and reference: H stands for Humphreys (1978), GS for Garmany and Stencel (1992), Z for de Zeeuw et al. (1999). - association distance (in parsecs) from Humphreys (1978); - association distance from Garmany & Stencel (1992); - association membership and distance from de Zeeuw et al. (1999); , - distance estimated from formula (3), and its formal error.