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Pre-main sequence star Proper Motion Catalogue
We measured the proper motions of 1250 pre-main sequence (PMS) stars andof 104 PMS candidates spread over all-sky major star-forming regions.This work is the continuation of a previous effort where we obtainedproper motions for 213 PMS stars located in the major southernstar-forming regions. These stars are now included in this present workwith refined astrometry. The major upgrade presented here is theextension of proper motion measurements to other northern and southernstar-forming regions including the well-studied Orion and Taurus-Aurigaregions for objects as faint as V≤16.5. We improve the precision ofthe proper motions which benefited from the inclusion of newobservational material. In the PMS proper motion catalogue presentedhere, we provide for each star the mean position and proper motion aswell as important photometric information when available. We providealso the most common identifier. The rms of proper motions vary from 2to 5 mas/yr depending on the available sources of ancient positions anddepending also on the embedding and binarity of the source. With thiswork, we present the first all-sky catalogue of proper motions of PMSstars.
| Revisiting Hipparcos data for pre-main sequence stars
We cross-correlate the Herbig & Bell and Hipparcos Catalogues inorder to extract the results for young stellar objects (YSOs). Wecompare the distances of individual young stars and the distance oftheir presumably associated molecular clouds, taking into accountpost-Hipparcos distances to the relevant associations and usingHipparcos intermediate astrometric data to derive new parallaxes of thepre-main sequence stars based on their grouping. We confirm that YSOsare located in their associated clouds, as anticipated by a large bodyof work, and discuss reasons which make the individual parallaxes ofsome YSOs doubtful. We find in particular that the distance of TaurusYSOs as a group is entirely consistent with the molecular clouddistance, although Hipparcos distances of some faint Taurus-Auriga starsmust be viewed with caution. We then improve some of the solutions forthe binary and multiple pre-main sequence stars. In particular, weconfirm three new astrometric young binaries discovered by Hipparcos:RY Tau, UX Ori, and IXOph. Based on observations made with the ESA Hipparcosastrometry satellite
| Radio emission from RASS sources south of Taurus-Auriga
We present a 8.4 GHz VLA survey of 50 optical counterparts to 46 ROSATAll-Sky survey (RASS) X-ray sources south of the Taurus-Aurigastar-forming region. This survey detected 3 sources with a sensitivitylimit of ~ 0.12 mJy. Merging our sample with other radio observations ofsources in and around Taurus-Auriga, we find scarce radio emission amongRASS sources south of the Taurus-Auriga molecular clouds. Our datasupport the evidence that these sources are older than weak-lined TTauri stars, most of them probably being close to the ZAMS.
| HIPPARCOS results for ROSAT-discovered young stars
Out of ~ 500 Lithium-rich ROSAT counterparts, which were presumed to below-mass pre-main sequence stars, 21 stars have been observed byHIPPARCOS. We study their parallaxes, proper motions, and photometricdata. For 7 out of 10 Taurus and Lupus stars in our sample, propermotions and parallaxes are not inconsistent with membership to theseassociations, while most of the stars in Chamaeleon and Scorpius appearto be young foreground stars. Combined with ground based photometry andspectroscopy, HIPPARCOS parallaxes allow us to place 15 stars on an H-Rdiagram. All these 15 stars lie above the Zero-Age-Main-Sequence andthus are indeed pre-main sequence stars with ages from 1 to 15 Myr. Onlytwo of the stars are located on the Hayashi-tracks, whereas the other 13are post-TTauri stars located on radiative tracks. Although the sampleis admittedly small, containing only 3% of the total sample ofLithium-rich ROSAT counterparts, it does not confirm recent predictionsby other authors: We find no stars in the age range from 20 to 100 Myr.The foreground pre-main sequence stars may have been ejected toward us,or they belong to the Gould Belt system, a plane filled with youngstars.
| Binary Search Among X-ray Active Stars South of the Taurus Molecular Cloud.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1555S&db_key=AST
| Search for young low-mass stars in a ROSAT selected sample south of the Taurus-Auriga molecular clouds
We present results of intermediate resolution spectroscopy of 131optical counterparts to 115 ROSAT All-Sky Survey X-ray sources south ofthe Taurus-Auriga dark cloud complex. These objects have been selectedas candidate young stars from a total of 1084 ROSAT sources in a ~300square degree area. We identify 30 objects as low-mass PMS stars on thebasis of the Li i, lambda 6708 Angstroms doublet in their spectrum, asignature of their young age. All these stars have a spectral type laterthan F7 and show spectral characteristics typical of weak-line andpost-T Tauri stars. The presence of young objects several parsecs awayfrom the regions of ongoing star formation is discussed in the light ofthe current models of T Tauri dispersal. Based on observations made withthe Isaac Newton Telescope operated on the island of La Palma by theRoyal Greenwich Observatory in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias and with the ESO1.52m telescope on La Silla, Chile, operated by the European SouthernObservatory. Tables 1,2,3,4 are also available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Optical high-resolution spectroscopy of ROSAT detected late-type stars south of the Taurus molecular clouds.
We study 111 late-type stars found with optical follow-up observationsof ROSAT All-Sky Survey sources south of the Taurus molecular clouds.Some 30 of them have been claimed to be weak-line T Tauri stars,low-mass pre-main sequence (PMS) stars, based mainly on the presence ofstrong lithium 6708Å absorption in intermediate-resolution(~1Å) spectra. We obtained single-order echelle spectra at bluewavelengths for 106 of these stars, in order to measure their radial androtational velocities, and investigate their angular momentum evolutionand kinematic membership to the Taurus clouds. In addition, we obtainedechelle spectra with high (~0.25Å) resolution for seven stars tomeasure precisely the lithium equivalent width Wlambda_(Li).We find that ~1Å resolution is sufficient in order not tooverestimate Wlambda_(Li), e.g. due to blending. Of our 111stars, 19 are located on the λ Ori cloud, nine of which areK-type stars with lithium in excess of the zero-age-main-sequence (ZAMS)level, i.e. are PMS stars. At least 40 of the remaining 92 off-cloudstars display detectable lithium, 24 of which are lithium-excess stars,i.e. show lithium at least as strong as IC 2602 stars with the samespectral types. Of those 24 stars, nine (25% of the off-cloud stars withdetectable lithium) are PMS stars isolated from cloud material; all havespectral type K, and three of them are spectroscopic binaries. 15off-cloud stars have spectral type G and lithium comparable to IC 2602stars, i.e. may have already arrived on the ZAMS just like G-type IC2602 stars. However, all these 24 off-cloud lithium-excess stars areprobably not older than IC 2602 (~3x10^7^yrs). We discuss possible sitesand modes of origin of the isolated PMS stars south of Taurus.
| New proper motions of pre-main sequence stars in Taurus-Auriga
We present proper motions of 72 T Tauri stars located in the centralregion of Taurus-Auriga (Tau-Aur). These proper motions are taken from anew proper motion catalogue called STARNET. Our sample comprises 17classical T Tauri stars (CTTS) and 55 weak-line T Tauri stars (WTTS),most of the latter discovered by ROSAT. 53 stars had no proper motionmeasurement before. Kinematically, 62 of these stars are members of theassociation. A velocity dispersion of less than 2-3km/s is found whichis dominated by the errors of the proper motions. This velocitydispersion correlates with a spread in distances. Furthermore we presentproper motions of 58 stars located in a region just south of the Taurusmolecular clouds and compare the kinematics of the youngest stars inthis sample (younger than 3.5x10^7^yrs) with the kinematics of thepre-main sequence stars (PMS) in the Taurus-Auriga association. From acomparison of the space velocities we find that the stars in the centralregion of Tau-Aur are kinematically different from the stars in thesouthern part. Among the stars with large proper motions far off theTaurus mean motion we find 2 Pleiades candidates and 7 possible Pleiadesrunaway stars.
| New optical positions and proper motions of late type stars associated with SiO masers
The 33 cm astrograph of the Bordeaux Observatory has been used to derivewith respect to AGK3 reference stars, accurate positions of late typevariable stars variable stars associated with strong SiO maser emission.It is suggested that selected maser stars can be used to link theHIPPARCOS system and the VLBI extragalactic reference frame. The propermotions of the program (SiO) and reference stars are derived and, forthe program stars, are compared to the McCormick catalog of propermotions.
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