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Astron. Astrophys. 320, 185-195 (1997)

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7. Spatial distribution and age

In Fig. 4 we plot the spatial distribution of TTS in Lupus, with stars in three different (arbitrary chosen) age bins [FORMULA] coded by different symbols. Evidently, although many of the stars found at large distances from the clouds are comparatively old, there seems to be a significant fraction of stars which are younger than [FORMULA] yrs, yet located at distances of up to [FORMULA] from the Lupus dark clouds (which are marked by the optically selected TTS). If these stars have been formed in the vicinity of the dark clouds, a velocity of at least [FORMULA] is required for them to reach their present location, thus implying a velocity dispersion of [FORMULA] km/s. This value is in excess of typical velocity dispersions of [FORMULA], as found in SFRs like Taurus-Auriga (Jones & Herbig   1979 ) and Chamaeleon (Dubath et al.  1995). A possible explanation might be dynamical interactions in multiple TTS systems, producing run-away stars with high velocities (Sterzik et al.  1995 , Sterzik & Durisen  1995 ). Also in-situ formation in small cloudlets, which have dispersed by now, has been suggested (Feigelson  1996 ). Young stars at quite large distances from dark clouds have also been found south of the Taurus-Auriga SFR (Neuhäuser et al.  1995b ).

[FIGURE] Fig. 4. Plot of the spatial distribution of TTS in Lupus. Right panel: optically selected TTS known prior to ROSAT, left panel: X-ray selected TTS discovered by ROSAT. Stars younger than [FORMULA] are denoted by filled squares, stars in the range [FORMULA] by open squares, and stars older than [FORMULA] by starred symbols. Also plotted are the two lowest contours of the CO map of Murphy et al. (1986). Note that the CO map covers only part of the area where TTS have been found.
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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998