Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A Catalog of Temperatures and Red Cousins Photometry for the Hyades
Using Hyades photometry published by Mendoza and other authors,Pinsonneault et al. have recently concluded that Cousins V-I photometrypublished by Taylor & Joner is not on the Cousins system. Extensivetests of the Taylor-Joner photometry and other pertinent results aretherefore performed in this paper. It is found that in part, thePinsonneault et al. conclusion rests on (1) a systematic error inMendoza's (R-I)J photometry and (2) a small error in anapproximate Johnson-to-Cousins transformation published by Bessell. Forthe Taylor-Joner values of (V-R)C, it is found that there arepossible (though not definite) differences of several mmag with otherresults. However, the Taylor-Joner values of (R-I)C data aresupported at the 1 mmag level. Using the (R-I)C data andother published results, an (R-I)C catalog is assembled for146 Hyades stars with spectral types earlier than about K5. For singlestars with multiple contributing data, the rms errors of the catalogentries are less than 4.4 mmag. Temperatures on the Di Benedettoangular-diameter scale are also given in the catalog and are used tohelp update published analyses of high-dispersion values of [Fe/H] forthe Hyades. The best current mean Hyades value of [Fe/H] is found to be+0.103+/-0.008 dex and is essentially unchanged from its previous value.In addition to these numerical results, recommendations are made aboutimproving attitudes and practices that are pertinent to issues likethose raised by Pinsonneault et al.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| A New Procedure for the Photometric Parallax Estimation
We present a new procedure for photometric parallax estimation. The datafor 1236 stars provide calibrations between the absolute magnitudeoffset from the Hyades main-sequence and the ultraviolet-excess foreight different (B-V)0 colour-index intervals, (0.3 0.4),(0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8 0.9), (0.9 1.0) and(1.0 1.1). The mean difference between the original and estimatedabsolute magnitudes and the corresponding standard deviation are rathersmall, +0.0002 and +/-0.0613 mag. The procedure has been adapted to theSloan photometry by means of colour equations and applied to a set ofartificial stars with different metallicities. The comparison of theabsolute magnitudes estimated by the new procedure and the canonical oneindicates that a single colour-magnitude diagram does not supplyreliable absolute magnitudes for stars with large range of metallicity.
| A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
Hipparcos parallaxes fix distances to individual stars in the Hyadescluster with an accuracy of ~ 6 percent. We use the Hipparcos propermotions, which have a larger relative precision than the trigonometricparallaxes, to derive ~ 3 times more precise distance estimates, byassuming that all members share the same space motion. An investigationof the available kinematic data confirms that the Hyades velocity fielddoes not contain significant structure in the form of rotation and/orshear, but is fully consistent with a common space motion plus a(one-dimensional) internal velocity dispersion of ~ 0.30 kms-1. The improved parallaxes as a set are statisticallyconsistent with the Hipparcos parallaxes. The maximum expectedsystematic error in the proper motion-based parallaxes for stars in theouter regions of the cluster (i.e., beyond ~ 2 tidal radii ~ 20 pc) isla 0.30 mas. The new parallaxes confirm that the Hipparcos measurementsare correlated on small angular scales, consistent with the limitsspecified in the Hipparcos Catalogue, though with significantly smaller``amplitudes'' than claimed by Narayanan & Gould. We use the Tycho-2long time-baseline astrometric catalogue to derive a set of independentproper motion-based parallaxes for the Hipparcos members. The newparallaxes provide a uniquely sharp view of the three-dimensionalstructure of the Hyades. The colour-absolute magnitude diagram of thecluster based on the new parallaxes shows a well-defined main sequencewith two ``gaps''/``turn-offs''. These features provide the first directobservational support of Böhm-Vitense's prediction that (the onsetof) surface convection in stars significantly affects their (B-V)colours. We present and discuss the theoretical Hertzsprung-Russelldiagram (log L versus log T_eff) for an objectively defined set of 88high-fidelity members of the cluster as well as the delta Scuti startheta 2 Tau, the giants delta 1, theta1, epsilon , and gamma Tau, and the white dwarfs V471 Tau andHD 27483 (all of which are also members). The precision with which thenew parallaxes place individual Hyades in the Hertzsprung-Russelldiagram is limited by (systematic) uncertainties related to thetransformations from observed colours and absolute magnitudes toeffective temperatures and luminosities. The new parallaxes providestringent constraints on the calibration of such transformations whencombined with detailed theoretical stellar evolutionary modelling,tailored to the chemical composition and age of the Hyades, over thelarge stellar mass range of the cluster probed by Hipparcos.
| Internal velocity dispersion in the Hyades as a test for Tycho-2 proper motions
The Hyades stars have highly coherent motions in space which reflect inthe convergence of their astrometric proper motions in or about a commonconvergent point. The internal dispersion of the Hyades velocities is aslow as about 0.3 km s-1. This is comparable with the expecteduncertainty of the Tycho-2 proper motion at the distance of the Hyades.The classical approach of using the proper motion components normal tothe convergent point direction is employed for some 200 bona fidecluster members located in an area of some 2 000 deg2 andranging in V magnitude 3.4 to 12.1. It is demonstrated that with themost precise Tycho-2 proper motions for some 50 stars, the intrinsicdispersion is measurable at the level of 0.32 km s-1, inagreement with previous estimations obtained from the Hipparcos data andradial velocities. When only 30 stars out of the 50 are considered,which are not known to be spectroscopic binaries, the observed scattersuggests a dispersion of only 0.22 km s-1. The approach inuse is model independent, and sets an upper limit on the intrinsicdispersion of velocities. It is shown for some 180 stars in common, thatthe Tycho-2 proper motions have a very similar precision to that ofHipparcos, but reveal fewer extreme deviants from the common convergentpoint direction. Tycho-2 proper motions are based on long series ofobservations, up to a 100 years, and are therefore less subject to theorbital motion effects in binaries. The ratio of the external error tothe formal error of the Tycho-2 proper motions may be up to 1.3 forstars fainter than V_T=8.5 mag. An alternative explanation for the extrascatter in low-precision subsets is discussed, that less massive starsmay indeed have larger observed velocity dispersion due to the binarityeffect. Based on observations made with the ESA Hipparcos satellite.
| A Precision Test of HIPPARCOS Systematics toward the Hyades
We propose a test that can in principle detect any systematic errors inthe Hipparcos parallaxes toward the Hyades cluster at the level of 0.3mas. We show that the statistical parallax algorithm subsumes theclassical moving cluster methods and provides more precise estimates ofthe distance and the first two moments of the velocity distribution ofthe Hyades cluster, namely, its bulk space velocity and the velocitydispersion tensor. To test the Hipparcos parallaxes, we first rescalethe bulk velocity determined from statistical parallax to forceagreement with the distance scale determined from Hipparcos parallaxes.We then predict the parallaxes of Hyades cluster members using thiscommon cluster space velocity and their Hipparcos proper motions. Weshow that the parallaxes determined in this manner (pi_pm) areconsistent at the 1 sigma level with the parallaxes (pi_orb) of threeHyades spectroscopic binary systems with orbital solutions. We find that=0.52+/-0.47 mas, where the error is dominated bythe errors in the orbital parallaxes. A reduction in these errors wouldallow a test of the systematic errors in the Hipparcos parallaxes at the0.3 mas level. If the Hyades distance scale is fixed by Hipparcosparallaxes, then its bulk velocity in equatorial coordinates is(V_x,V_y,V_z)=(-5.70+/-0.20, 45.62+/-0.11, 5.65+/-0.08) kms^-1, itsvelocity dispersion is 320+/-39 m s^-1, and the distance modulus to thecentroid of our sample of 43 cluster members is 3.34+/-0.02 mag.
| Color indices of the Sun and Hyades stars in the WBVR system
Using an original setup at high altitudes, we measured the color indicesof the Sun in the WBVR photometric system relative to standard stars: (W- B)_solar = -0.05, (B - V)_solar = +0.67, and (V - R)_solar = +0.53. Wepresent the WBVR photometry for the Hyades members selected by vanBueren by their space velocities. The solar position is shown intwo-color diagrams relative to Hyades stars and bright G2 V stars. Acomparison of our results with Kurucz's models reveals a discrepancybetween the metallicities of the models and the Hyades members.
| The Hyades: distance, structure, dynamics, and age
{We use absolute trigonometric parallaxes from the Hipparcos Catalogueto determine individual distances to members of the Hyades cluster, fromwhich the 3-dimensional structure of the cluster can be derived.Inertially-referenced proper motions are used to rediscuss distancedeterminations based on convergent-point analyses. A combination ofparallaxes and proper motions from Hipparcos, and radial velocities fromground-based observations, are used to determine the position andvelocity components of candidate members with respect to the clustercentre, providing new information on cluster membership: 13 newcandidate members within 20 pc of the cluster centre have beenidentified. Farther from the cluster centre there is a gradual mergingbetween certain cluster members and field stars, both spatially andkinematically. Within the cluster, the kinematical structure is fullyconsistent with parallel space motion of the component stars with aninternal velocity dispersion of about 0.3 km s(-1) . The spatialstructure and mass segregation are consistent with N-body simulationresults, without the need to invoke expansion, contraction, rotation, orother significant perturbations of the cluster. The quality of theindividual distance determinations permits the cluster zero-age mainsequence to be accurately modelled. The helium abundance for the clusteris determined to be Y =3D 0.26+/-0.02 which, combined with isochronemodelling including convective overshooting, yields a cluster age of625+/-50 Myr. The distance to the observed centre of mass (a conceptmeaningful only in the restricted context of the cluster memberscontained in the Hipparcos Catalogue) is 46.34+/-0.27 pc, correspondingto a distance modulus m-M=3D3.33+/-0.01 mag for the objects within 10 pcof the cluster centre (roughly corresponding to the tidal radius). Thisdistance modulus is close to, but significantly better determined than,that derived from recent high-precision radial velocity studies,somewhat larger than that indicated by recent ground-based trigonometricparallax determinations, and smaller than those found from recentstudies of the cluster convergent point. These discrepancies areinvestigated and explained. } Based on observations made with the ESAHipparcos astrometry satellite. Table~2 is also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Seven-Color Photoelectric Photometry of Stars in the Hyades Clusters
Not Available
| Photometric and spectroscopic monitoring of AA Tau, DN Tau, UX Tau A, T Tau, RY Tau, LK CA 4, and LK CA 7
We report the results of a UBVRI photometric monitoring campaign forthree classical T Tauri stars (AA Tau, DN Tau, and UX Tau A) and twoweak emission line T Tauri stars (Lk Ca 4 and Lk Ca 7). Observationswere obtained at three sites during a core observing period spanning UT1985 October 14 through UT 1985 December 25, with additionalobservations continuing until UT 1986 April 6. Concurrentspectrophotometric observations were obtained for all main program starsexcept Lk Ca 7 and additionally for T Tau, RW Aur, and RY Tau. Periodicphotometric variability, assumed to be the stars' rotation periods, werefound for AA Tau, DN Tau, Lk Ca 4, and Lk Ca 7, respectively, as 8.2,6.3, 3.4, and 5.7 days. Several U-filter flares were observed for Lk Ca4 and Lk Ca 7, which are strongly concentrated toward phases of minimumlight. Correlations are found between H-alpha line strengths and Vmagnitudes for AA Tau and RY Tau. An analysis of absolute colorvariations of classical T Tauri stars confirms that hot spots are thepredominant cause of these stars' variability. Our overall results areconsistent with earlier findings that long-lived cool spots areresponsible for most of the variability found for weak-emission T Tauristars, while temporal hot spots are primarily responsible for theobserved variability found in classical T Tauri stars.
| The distance and main sequence of the Hyades cluster based on 145 stars with highly accurate proper motions obtained from work on the catalogues FK 5 and PPM
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&A...243..386S&db_key=AST
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
| Determining the temperatures of solar-type stars - Do star spots produce color anomalies?
The available evidence pertaining to color 'anomalies' in Hyades dwarfsare examined in detail in order to understand how the determine thetemperatures of solar-type stars. The evidence indicates that thetemperatures of these stars are not seriously skewed by their spots.Simpler explanations which can produce the observed effects arediscussed.
| Additional UBVRI photometric searches for periodic light variability from T Tauri stars
UBVRI photometric monitoring of five T Tauri stars (DH Tau, DI Tau, GGTau, AA Tau, and HP Tau) and one weak-emission pre-main-sequence star(HP Tau/G2) have been carried out in an effort to determine rotationperiods via rotational modulation of surface hot and cool regions.Rotation periods of 7.2, 7.9, 8.2, and 1.2 days were found for DH Tau,DI Tau, AA Tau, and HP Tau/G2, respectively. Consistent with the resultsof previous studies, the spots on the strong-emission (T Tauri) starsappear to be hot relative to the stellar photospheres, while those onthe weak-emission stars are cooler than the photospheres. The hotregions appear to be the cause of both periodic and aperiodic lightvariability in T Tauri stars on timescales of days and weeks.Spectrophotometry concurrent with the photometric monitoring wasobtained on several nights for many of the stars. While no correlationsbetween stellar brightness and H-alpha emission could be found for anyindividual star, H-alpha equivalent-width variability correlates wellwith photometric variability from star to star.
| A radial-velocity survey of the Hyades
Photoelectric radial-velocity measurements, obtained with external erroras small as 0.1 km/s using the 200-inch Hale telescope at PalomarObservatory during the period 1971-1986, are reported for over 400candidate members (with V magnitude between 6 and 14) of the Hyadescluster. The history of Hyades observations is recalled; the Palomarinstrumentation and observing program are described; the data-reductionand standardization procedures are discussed in detail; and the data arepresented in extensive tables and graphs. About 200 of the stars areclassified as cluster members, including 60 spectroscopic binaries.
| Magnetic field structure in the Taurus dark cloud
Optical and infrared polarimetry of sources in the direction of theTaurus cloud are obtained in order to study the magnetic field in thiscloud and its possible role in the cloud's evolution. Most of the starsare background giant stars whose light shines through the cloud and ispolarized by the cloud material. The transverse component of themagnetic field, as delineated by the polarization vectors, is generallyperpendicular to the galactic plane, and the stratified structure of thecloud could be due to the effect of the magnetic field during the earlystages of collapse. Three of the 13 embedded stars are stronglypolarized with position angles nearly perpendicular to those of nearbyfield stars. The polarization of these stars is most likely intrinsic,and the direction of polarization indicates that the materialsurrounding these stars may be magnetic i.e., that the magnetic field isfrozen in this material.
| UBVRI monitoring of five late-type pre-main-sequence stars
Two T Tauri stars (DF Tau and DK Tau) and three pre-main-sequence Kstars with weak line emission (WK X-Ray 1, WK X-Ray 2, and FK X-Ray 3)were monitored with UBVRI photometry over a 14-night period duringOctober 1982. Neither T Tauri star shows an obvious rotationalmodulation in the light curve, but DF Tau did experience a multi-dayflare-like brightening similar to the events seen in this star byZajtseva and Lyutyi (1976). The light variations of the threeweak-emission stars are well described by sine curves with periods of5.6, 2.8, and 7.0 days, respectively; these values presumably representthe axial rotation periods of these stars. The results provide furtherevidence for K-type pre-main-sequence stars which rotate at least asfast as T Tauri stars but lack strong line and continuum emission.
| The sun among the stars. V - A second search for solar spectral analogs: The Hyades' distance
A five-part search for a match of the solar spectrum throughout the sky,down to the limit of the Bright Star Catalog, is completed by 20A-resolution comparisons of G-type star photoelectric violet spectrawith those of Jupiter satellites and the blue sky. It is confirmed thatsolar analogs are rare. The strengths, relative to the sun, of theabsorption features at 3850 and 3740 A are measured quantitatively forall 164 stars observed. Their dependence on B-V and U-V leads to thesame solar colors previously derived from the solar analogs alone, withB-V equals 0.66 and U-B equals 0.20. Giants and subgiants are excludedfrom consideration, and stellar metal content dependence was closelyobserved. The sun is found to fit the mass-luminosity relation of theHyades within 0.16 m, independent of the assumed helium abundance, ifevolutionary and metal abundance effects are taken into account.
| New members of the Hyades cluster and a discussion of its structure.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&A....43..423P&db_key=AST
| Calibration of the Hyades-Praesepe main sequence by a new treatment of the stellar motions.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75.1097U&db_key=AST
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| The Color-Magnitude Diagram of the Hyades Cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962ApJ...136...75J&db_key=AST
| The Hyades and Coma Berenices Star Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJ...122..209J&db_key=AST
| On the structure of the Hyades cluster
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 04h40m49.07s |
| Declinazione: | +23°48'34.6" |
| Magnitudine apparente: | 8.85 |
| Distanza: | 51.335 parsec |
| Moto proprio RA: | 61.8 |
| Moto proprio Dec: | -48.5 |
| B-T magnitude: | 9.682 |
| V-T magnitude: | 8.919 |
Cataloghi e designazioni:
|
