Astron. Astrophys. 361, 1143-1151 (2000)

1. Introduction

Analysis of the motion of pre-main sequence (PMS) stars and of related groups of young stars provide essential tests of star formation models. Different space velocities and velocity gradients of the stellar associations can be derived from the major star formation scenarios, like sequential star formation, star formation by high-velocity clouds, Gould's Belt models, etc. Proper motion measurements of the members of these associations provide one way to discriminate among these predictions. The PMS stars are supposed to be sufficiently young to be very close to their birthplaces and to have velocities still very similar to the initial ones, so that one can get clear constraints on the birth mechanism.

In this work, we investigated the PMS stars of an extended region of aligned molecular clouds and OB associations that includes the Chamaeleon, Lupus, Upper Scorpius - Ophiuchus and Corona Australis regions. This selected area is specially interesting because the associations are close enough to the Sun (100-150 pc), so that a refined kinematical study can be made.

The HIPPARCOS mission (ESA 1997) provided accurate measurements of positions, parallaxes and proper motions, for OB stars brighter than V=10 mag, allowing to study the kinematics of the same regions (de Zeeuw et al. 1999). Proper motions of PMS stars associated with these star-forming complexes, based on HIPPARCOS data, were recently obtained (Frink et al. 1998, Neuhäuser & Brandner 1998, Wichmann et al. 1998, Bertout et al. 1999), providing a first comparison of space velocities of different groups of stars. However, since most PMS stars are fainter than the limiting magnitude of HIPPARCOS, the total number of measured PMS stars is still small.

In this work, we present proper motion determination for 213 PMS stars as faint as V16 mag lying in the galactic longitude range to .

In the following sections, we present the method used to derive proper motions based on different combinations of first and second epoch measurements, we discuss the quality of our results and present a first analysis of this large sample of proper motions obtained for the PMS stars.

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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