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The Lupus Association of Pre-Main-Sequence Stars: Clues to Star Formation Scattered in Space and Time
Kinematical analysis of spectroscopically identified pre-main-sequencestars associated with the Lupus dark cloud reveals a streamlike motionof low internal velocity dispersion (<=1.3 km s-1). Astatistically significant mismatch between the convergent point radialvelocity and the spectroscopic radial velocity from the literatureindicates a moderate degree of expansion. The rate of expansion is toolow to account for the present extent of the association if one assumesthat the spatially dispersed population was formed in the densemolecular cores observed today. Therefore, it is unlikely that theoutlying weak-lined T Tauri members were born in the same star-formingcores as the more compactly located classical T Tauri stars, despite thekinematic integrity of the association. Distances inferred from theclassical moving-cluster method show a large depth of the association(~80 pc) along the line of sight. A color-magnitude diagram of theassociation in the near-IR colors corrected for the distribution ofdistances shows a clear gap separating the older (5-27 Myr) and theyounger (~1 Myr) generations of stars. Half of the identified 1 Myr oldstars lie in the tight group of mostly classical T Tauri starsassociated with the Lupus 3 dark filament. This nest of very young starsappears to be 25 pc farther from the Sun than the center of the greaterLupus association.
| 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.
| Proper motions of pre-main sequence stars { } in southern star-forming regions
We present proper motion measurements of pre-main sequence (PMS) starsassociated with major star-forming regions of the southern hemisphere(Chamaeleon, Lupus, Upper Scorpius - Ophiuchus, Corona Australis),situated in the galactic longitude range l = 290degr to l = 360degr . Alist of PMS stars as complete as possible was established based on theHerbig and Bell catalogue and many new catalogues like the PDS survey,the catalogue of Herbig Ae/Be stars by Thé et al. (\cite{the}),X-rays surveys, etc. The measurements made use of public material(mainly AC2000 and USNO-A2.0 catalogues) as well as scans of SERC-JSchmidt plates with the MAMA measuring machine (Paris) and Valinhos CCDmeridian circle observations (Brazil). We derived proper motions for 213stars, with an accuracy of 5 to 10 mas/yr depending mainly on thedifference of epochs between the position sources. The maincharacteristics of the sample are discussed. We show that systematicmotions of groups of stars exist, which are not explained by the reflexsolar motion. Based on observations made at Valinhos CCD MeridianCircle. Based on measurements made with MAMA automatic measuringmachine. Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| High-resolution spectroscopy of ROSAT-discovered weak-line T Tauri stars near Lupus
We present high-resolution optical echelle spectroscopy for a largefraction of the Li-rich late-type stars recently discovered in thevicinity of the Lupus dark clouds. Our results confirm the highLiilambda6708 equivalent widths previously estimated frommedium-resolution spectra, thus adding strength to the conclusion thatthe large majority of these stars are still in the pre-main-sequencephase of their evolution, contrary to claims from other authors thatmany of them might be zero-age main-sequence stars. We present astatistical approach to derive a mean distance for the sample, and findthat it is consistent with, or slightly lower than, the Hipparcosdistance of the Lupus star-forming region. The radial velocitiesmeasured for part of these stars are consistent with those observed forthe Lupus star-forming region, while stars outside the dark clouds showa mean difference of the order of 3kms^-1. The projected rotationalvelocities show a lack of slow rotators, which is interpreted as aconsequence of the X-ray selection of the sample. The Li-rich stars inLupus studied in this work yield a fairly `clean' sample of very youngstars, while in other star-forming regions a larger fraction of olderzero-age main-sequence stars has been found among ROSAT-discoveredLi-rich stars. We argue that this fact reflects the relation of thesestars with the Gould Belt.
| 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.
| New "weak-line"--T Tauri stars in Lupus
We present first results obtained by a survey of the Lupus star formingregion in search of new T Tauri stars. This study has been performed onthe basis of deep pointed ROSAT observations in the Lupus dark clouds aswell as data from the ROSAT All-Sky-Survey in the surrounding, lessobscured regions. Our survey covers an area of about 230 square degrees,located between 15^h,6^m and 16^h,24^m$ in right ascension and between-47^\circ and -32^\circ in declination. Identification of ROSATAll-Sky-Survey sources in this area by means of optical spectroscopyrevealed 89 T Tauri stars, 86 of them "weak-line" T Tauri stars (WTTS)not known from previous studies of this region. Our pointed ROSATobservations led to the identification of 47 more T Tauri stars, givinga total of 136 new T Tauri stars. The large area of our study, ascompared with previous works, allows us to study the spatialdistribution of WTTS in this star forming region on a large scale. Wefind the new WTTS to be distributed over the whole area of our survey,indicating that their spatial distribution might extend well beyond ourstudy area. Contrary to the Lupus T Tauri stars known prior to thisstudy, the WTTS discovered by the ROSAT All-Sky-Survey are not clusteredin the regions of highest extinction, i.e. the dark clouds. Based onobservations collected at European Southern Observatory, La Silla, Chile(observing proposals ESO Nos. 49.7-0010, 50.7-0109, 51.7-0106,51.7-0029). Tables 5--12 are only available in electronic form at theCDS via anonymous ftp 130.79.128.5 or on www athttp://cdsweb.u-strasbg.fr/abstract.html.
| The T Tauri star population in the Lupus star forming region.
In a recent study, some 130 new weak-line T Tauri stars (WTTS) have beendiscovered in the Lupus star forming region (SFR). Some of these starsare seen projected onto regions of high obscuration, while others arelocated far from the Lupus dark clouds. In this paper we presentphotometric observations of a large sample of these WTTS. We estimateeffective temperatures and luminosities for the stars observed, andderive masses and ages by comparison with theoretical evolutionarytracks. The mean age of WTTS seen in projection against the dark cloudsis found to be lower than the mean age of WTTS discovered far fromregions of high obscuration, and yet higher than the mean age of theclassical T Tauri stars (CTTS) in Lupus. Moreover, while the CTTS inLupus show an unusual predominance of very low-mass stars, the WTTSpopulation in Lupus contains many stars with comparatively highermasses. Correlations between the X-ray emission and other stellarparameters, like bolometric luminosity, radius, mass, and age, arestudied, and the results are discussed.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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| קבוצת-כוכבים: | זאב |
| התרוממות ימנית: | 16h04m57.07s |
| סירוב: | -38°57'15.7" |
| גודל גלוי: | 9.169 |
| תנועה נכונה: | -27.8 |
| תנועה נכונה: | -46.8 |
| B-T magnitude: | 9.812 |
| V-T magnitude: | 9.223 |
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