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Astron. Astrophys. 338, 442-451 (1998)

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5. Summary and conclusions

We have analysed proper motions from the Hipparcos, ACT and STARNET catalogues for altogether 45 stars, 22 of which are bona-fide pre-main sequence stars and 23 are of dubious PMS nature or ZAMS stars. On the basis of the distribution of the proper motions the presence of several subgroups in our data is suggested, which roughly coincide with similar groups on the sky. Given the kinematic distances which are independently confirmed by the Hipparcos parallaxes, the two subgroups might belong to distinct structures of the Chamaeleon clouds.

There is no indication in these data for a slow dispersal of stars out of the active cloud cores, and so the model proposed by Sterzik & Durisen (1995) cannot account for the large distribution of WTTS observed far from any known cloud material. However, the observed motions are more or less consistent with the high velocity cloud impact model of Lépine & Duvert (1994) if the stars are currently at their turning point. Similarly, the data could be interpreted in terms of the cloudlet model (Feigelson 1996) where star formation takes place far off the active cloud cores and which produces small groups of TTS with low internal velocity dispersions, but high relative velocities between groups.

Larger proper motion catalogues produced hopefully by future space missions like DIVA or GAIA will help to settle the question of the formation scenario of this large population of weak-line T Tauri stars in the Chamaeleon region.

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© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998