J/A+A/341/L79 J/A+A/341/L79 Proper motions of faint ROSAT WTT stars L Terranegra F Morale A Spagna G Massone M G Lattanzi Astron. Astrophys. 341, L79 ??? ??? 1999 1999A+A...341L..79T I/239 : The Hipparcos and Tycho Catalogues (ESA 1997) I/246 : The ACT Reference Catalog (Urban+ 1997) I/146 : Positions and Proper Motions - North (Roeser+, 1988) I/193 : Positions and Proper Motions - South (Bastian+ 1993) J/A+AS/114/109 : Cha X-ray sources + optical identifications (Alcala+ 1995) Proper motions Radio sources Stars, late-type astrometry stars: fundamental parameters stars: kinematics stars: late-type stars: pre-main sequence We present proper motions of 59 stars of the ROSAT All-Sky Survey (RASS) located in direction of the Chamaeleon star forming region (SFR) in the magnitude range B=5.1-17mag. Proper motions of the fainter stars were newly derived utilizing survey Schmidt plates from the GSC~II plate archive and from a set of special plates taken with the ESO Schmidt telescope. The vector point diagram (VPD) indicates that the certified weak emission-line T Tauri (WTT) stars cluster away from the region occupied by the brighter pre-main-sequence stars (PMS) in Cha I. The distance to this new association is estimated at ~100pc, sensibly smaller than the 150pc generally assumed for the SFR. This yields an upper limit of 2km/s for the velocity dispersion of this new kinematic group. The de-reddened CM diagram of the group members suggest the WTT stars are still PMS objects, but older (3-30Myr) and less massive than previous determinations. These revised age estimates, the newly derived group peculiar velocity, and current distance estimates to the Cha~I/II/III complex would favour 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 as a result of more classical mechanisms like interactions with the spiral arms.

ROSAT

Name ROSAT all-sky survey source designation Alcala' et al. (1995, Cat. <J/A+AS/114/109>) or catalogue designation --- n_Name Note on Name number=1 *: The proper motion value for CED 110 is from Grasdalen G. (1977IAUC...42...25G), while the values for SAO 256557 and RXJ1225.3-7857 are from the original catalogue and they are in the FK5 system. However the deviation from the Hipparcos system can be considered negligible in this work. KG: Stars belong to the kinematical group (see text). --- CatNo Astrometric catalog designation --- Cat Catalogue name number=2 A = ACT Catalog (Cat. <I/246>) P = PPM Catalog (Cat. <I/146>, <I/193>) H = Hipparcos Catalog (Cat. <I/239>) S = GSC S039 plate --- pmRA Proper motion in right ascension ({mu}RA*cosDE}) mas/yr e_pmRA rms uncertainty on pmRA mas/yr pmDE Proper motion in declination mas/yr e_pmDE rms uncertainty on pmDE mas/yr plx Parallax from Hipparcos catalogue (<I/239>) mas e_plx rms uncertainty on plx mas SpType Spectral Type --- Vmag Stellar V magnitude mag Type Stellar type number=3 PMS: Pre-Main Sequence stars from the high resolution spectroscopy by Covino et al. (1997A&A...328..187C) W: WTTS from low resolution spectroscopy by Alcala' et al. (1995, Cat. <J/A+AS/114/109>) UBS: uncorrelated bright stars by Alcala' et al. (1995, Cat. <J/A+AS/114/109>) CTTS: Classical T Tauri stars Ae/Be: Herbig Ae/Be stars --- Names Other names --- table1.psPostScript version of table1 table1.texLaTeX version of table1 Patricia Bauer CDS 1999Jan08Luciano Terranegra <TERRANEGRA@astrna.na.astro.it> J_A+A_341_L79.xml