Proper motions of faint ROSAT WTT stars in the Chamaeleon region

We present proper motions of 59 stars of the ROSAT All-Sky Survey (RASS) lo cated in direction of the Chamaeleon star forming region (SFR) in the magni tude range B=5.1 - 17 mag. Proper motions of the fainter stars were newly d erived utilizing survey Schmidt plates from the GSC II plate archive and fr om a set of special plates taken with the ESO Schmidt telescope. The vector point diagram (VPD) indicates that the certified WTT stars cluster away fr om the region occupied by the brighter pre-main-sequence stars (PMS) in Cha I. The distance to this new association is estimated at similar to 100 pc, sensibly smaller than the 150 pc generally assumed for the SFR. This yield s an upper limit of 2 km s(-1) for the velocity dispersion of this new kine matic group. The de-reddened CM diagram of the group members suggest the WTT stars are s till PMS objects, but older (3-30 Myr) and less massive than previous deter minations. These revised age estimates, the newly derived group peculiar ve locity, and current distance estimates to the Cha I/II/III complex would fa vour in-situ formation against that predicted by high velocity cloud models . Finally, based on a redetermination of the peculiar motions of stars and gas, we speculate that the whole SFR originated from the local Orion spur a s a result of more classical mechanisms like interactions with the spiral a rms.