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A kinematic study of the Taurus-Auriga T association
Aims.This is the first paper in a series dedicated to investigating thekinematic properties of nearby associations of young stellar objects.Here we study the Taurus-Auriga association, with the primary objectiveof deriving kinematic parallaxes for individual members of this low-massstar-forming region. Methods: .We took advantage of a recentlypublished catalog of proper motions for pre-main sequence stars, whichwe supplemented with radial velocities from various sources found in theCDS databases. We searched for stars of the Taurus-Auriga region thatshare the same space velocity, using a modified convergent point methodthat we tested with extensive Monte Carlo simulations. Results:.Among the sample of 217 Taurus-Auriga stars with known proper motions,we identify 94 pre-main sequence stars that are probable members of thesame moving group and several additional candidates whose pre-mainsequence evolutionary status needs to be confirmed. We derive individualparallaxes for the 67 moving group members with known radial velocitiesand give tentative parallaxes for other members based on the averagespatial velocity of the group. The Hertzsprung-Russell diagram for themoving group members and a discussion of their masses and ages arepresented in a companion paper.
| 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.
| Lick Northern Proper Motion Program. III. Lick NPM2 Catalog
The Lick Northern Proper Motion (NPM) program, a two-epoch (1947-1988)photographic survey of the northern two-thirds of the sky(δ>~-23deg), has measured absolute proper motions,on an inertial system defined by distant galaxies, for 378,360 stars inthe magnitude range 8<~B<~18. The 1993 NPM1 Catalog contains148,940 stars in 899 fields outside the Milky Way's zone of avoidance.The 2003 NPM2 Catalog contains 232,062 stars in the remaining 347 NPMfields near the plane of the Milky Way. This paper describes the NPM2star selection, plate measurements, astrometric and photometric datareductions, and catalog compilation. The NPM2 Catalog contains 122,806faint (B>=14) anonymous stars for astrometry and Galactic studies,91,648 bright (B<14) positional reference stars, and 34,868 ``specialstars'' chosen for astrophysical interest. The NPM2 proper motions areon the ICRS system, via Tycho-2 stars, to an accuracy of 0.6 masyr-1 in each field. The rms proper-motion precision is 6 masyr-1. Positional errors average 80 mas at the mean plateepoch 1968, and 200 mas at the NPM2 catalog epoch 2000. NPM2photographic photometry errors average 0.18 mag in B and 0.20 mag inB-V. The NPM2 Catalog and the updated (to J2000.0) NPM1 Catalog areavailable at the CDS Strasbourg data center and on the NPM Web site. TheNPM2 Catalog completes the Lick Northern Proper Motion program after ahalf-century of work by three generations of Lick Observatoryastronomers. The NPM Catalogs will serve as a database for research inGalactic structure, stellar kinematics, and astrometry.
| The 76th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1406 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Dusty Debris around Solar-Type Stars: Temporal Disk Evolution
Using ISO-ISOPHOT, we carried out a survey of almost 150 stars to searchfor evidence of emission from dust orbiting young main-sequence stars,both in clusters and isolated systems. Over half of the detections arenew examples of dusty stellar systems and demonstrate that such dust canbe detected around numerous stars older than a few times 106yr. Fluxes at 60 and either 90 or 100 μm for the new excess sourcestogether with improved fluxes for a number of IRAS-identified sourcesare presented. Analysis of the excess luminosity relative to the stellarphotosphere shows a systematic decline of this excess with stellar ageconsistent with a power-law index of -2.
| Photometric observations of weak-line T Tauri stars . II. WTTS in Taurus-Auriga, Orion and Scorpius OB2-2
We present uvby-$beta a photometry of 116 X-ray flux-selected activestars in the directions of the Orion (40), Taurus-Auriga (58) andScorpius OB2-2 (18) star forming regions. Additionally, we give near IRJHK photometry of 20 active stars in the Taurus-Auriga direction. Theprogram stars were selected from the R_\odotsat All Sky Survey andEINSTEIN X-ray surveys and are spectroscopically confirmed weak-line TTauri stars and weak-line T Tauri star candidates. The photometryconfirms the young nature of the program stars and also indicates that asignificant fraction of the sample could be foreground objects. The datagiven here probably represent the largest homogeneous uvby-beta a$photometric sample of new WTTS and WTTS candidates. Many objects in thesample are observed photometrically for the first time. Based onobservations collected at the Observatorio Astronómico Nacionalin Sierra San Pedro Mártir, Baja California, México.Tables 1-4 are also 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
| Multiplicity of T Tauri stars in Taurus after ROSAT
We surveyed a sample of 75 T Tauri stars in the Taurus star formingregion for companions. These stars were discovered with the help ofROSAT. The separation range covered is 0.13'' to 13'', where the lowerlimit is given by the diffraction limit of the telescope and the upperlimit by confusion with background stars. Combined with the results ofthe preceding survey by Leinert et al. (\cite{Leinert93}), we now havesurveyed a sample of 178 young stars in Taurus, 63 classical, 106weak-line, and 9 unclassified T Tauri stars. Within this sample, we find68 binaries, 9 triples, and 3 quadruples. After corrections to accountfor confusion with background stars and for a bias induced through X-rayselection, we count 74 binaries or multiples with a total of 85companions in 174 systems. This corresponds to a degree of multiplicity(number of binaries or multiples divided by number of systems) of(42.5+/- 4.9)%, or to a duplicity, measured by the number of companionsper system, of (48.9+/- 5.3)%, which is higher by a factor of (1.93+/-0.26) compared to solar-type main-sequence stars. We find no differencein duplicity between classical and weak-line T Tauri stars. There is adifference between close and wide pairs in the sense that close pairshave a flat distribution of flux ratios, while the flux ratios of widepairs are peaked towards small values.
| Radio Emission from ROSAT-discovered Young Stars in and around Taurus-Auriga
An 8.4 GHz VLA survey of 91 recently discovered lithium-rich late-typestars from the ROSAT All-Sky Survey and pointed observations ispresented. These objects lie in the vicinity of the Taurus-Aurigastar-forming region (d ~= 140 pc); however, some are dispersed nearly 30deg from known active star-forming cloud cores. This sample represents aspatially complete, flux-limited population of X-ray-bright young starsboth within and away from the primary Tau-Aur stellar nurseries. Of the91 sources, 29 are detected in this radio survey with a sensitivitylimit of ~0.15 mJy. If they are at the distance of the star-formingclouds, we find that 32% of widely distributed young stars with LX >=5 x 1028 ergs s-1 have radio luminosity densities in excess of 3.5 x1015 ergs s-1 Hz-1. This detection rate, the ranges of radio and X-rayluminosities, and the LR/LX ratios are consistent with known youngweak-lined T Tauri stars (ages ~106 yr) that reside within the Taurusmolecular clouds, but they are considerably higher than a zero-agemain-sequence population such as the Pleiades (age ~=7 x 107 yr). Theradio properties thus support the pre-main-sequence classification ofthe stars. They fitted well among other active young stars on theempirical LR versus LX diagram, implying that solar-type gyrosynchrotronactivity is the radio emission mechanism.
| 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.
| COYOTES IV: the rotational periods of low-mass Post-T Tauri stars in Taurus.
We monitored the light variations of 58 weak-line T Tauri stars inTaurus, recently discovered in the X-ray wavelength range during theROSAT All-Sky Survey. We derive photometric periods for 18 stars, allbut one being ascribed to rotational modulation by stellar spots. Theexception is a 37.6d period assigned to the orbital motion of a newpre-main sequence spectroscopic binary. Two thirds of the stars in oursample have an age larger than 10Myr and up to 40Myr, thus filling theobservational gap that previously existed between T Tauri stars onconvective tracks and ZAMS dwarfs for the determination of therotational evolution of young low-mass stars. The rotational periods arefound to range from 0.5 to 7.5-days, most periods being shorter than5-days. This result provides direct evidence for the spin up of solartype stars as they contract on pre-main sequence radiative tracks, aspredicted by recent models of angular momentum evolution. The paucity oflong periods (P>=5d, i.e., V_eq_<=10km/s) in the sample of post-TTauri stars leaves, however, the origin of the numerous slow rotatorsobserved in young clusters an open issue.
| New weak-line T Tauri stars in Taurus-Auriga.
On the basis of the ROSAT All-Sky-Survey, a study of the Taurus-Aurigastar forming region has been performed in order to search for hithertoundiscovered TTauri stars. Our study covers an area of about 280 squaredegrees, located between 4^h^ and 5^h^ in right ascension and between15deg and 34deg in declination. Identification of ROSAT All-Sky Surveysources in this area by means of optical spectroscopy revealed 2 newclassical T Tauri stars (CTTS) and 66 new weak-line-T Tauri stars (WTTS)with Wlambda_(Hα)<=10A. Additional pointed ROSATobservations led to the identification of 6 more WTTS and 2 CTTS, givinga total of 76 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. We find the WTTS ofour survey to be distributed over the whole region investigated. Thereis a noticeable decline of the surface density from south to northwithin our study area, but the spatial distribution extends mostprobably beyond our study region. No clustering towards the populationof TTauri stars known prior to ROSAT in Taurus-Auriga could be observed.We suggest that the WTTS found in our study might in part be somewhatolder than the previously known TTauri stars in Taurus-Auriga, and thattheir broad spatial distribution is due to the typical velocitydispersion of a few km/s measured for Taurus TTauri stars, in which casefor some of our WTTS an age on the order of 10^7^years would be requiredfor reaching the observed distances from the Taurus dark clouds. Weestimate a WTTS/CTTS ratio of about 6 within our study area, butconclude that because of the different spatial distribution of WTTS andCTTS this ratio will be most probably significantly larger for a moreextended area.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h31m16.86s |
| Deklináció: | +21°50'25.3" |
| Vizuális fényesség: | 10.812 |
| RA sajátmozgás: | 2.1 |
| Dec sajátmozgás: | -13.5 |
| B-T magnitude: | 11.783 |
| V-T magnitude: | 10.893 |
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