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Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is 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/430/165}
| Two Active Nuclei in 3C 294
The z=1.786 radio galaxy 3C 294 lies < 10" from a 12 mag star and hasbeen the target of at least three previous investigations using adaptiveoptics (AO) imaging. A major problem in interpreting these results isthe uncertainty in the precise alignment of the radio structure with theH- or K-band AO imaging. Here we report observations of the position ofthe AO guide star with the Hubble Space Telescope Fine Guidance Sensor,which, together with positions from the second United States NavalObservatory's CCD Astrograph Catalog (UCAC2), allow us to register theinfrared and radio frames to an accuracy of better than 0.1". The resultis that the nuclear compact radio source is not coincident with thebrightest discrete object in the AO image, an essentially unresolvedsource on the eastern side of the light distribution, as Quirrenbach andcoworkers had suggested. Instead, the radio source is centered about0.9" to the west of this object, on one of the two apparently real peaksin a region of diffuse emission. Nevertheless, the conclusion ofQuirrenbach and coworkers that 3C 294 involves an ongoing merger appearsto be correct: analysis of a recent deep Chandra image of 3C 294obtained from the archive shows that the nucleus comprises two X-raysources, which are coincident with the radio nucleus and the easternstellar object. The X-ray/optical flux ratio of the latter makes itextremely unlikely that it is a foreground Galactic star.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS5-26555. These observations areassociated with proposal 08315. Based in part on data collected atSubaru Telescope, which is operated by the National AstronomicalObservatory of Japan. Some of the data presented herein were obtained atthe W. M. Keck Observatory, which is operated as a scientificpartnership among the California Institute of Technology, the Universityof California and the National Aeronautics and Space Administration. TheObservatory was made possible by the generous financial support of theW. M. Keck Foundation. Some of the data were also obtained from theChandra Data Archive, part of the Chandra X-Ray Observatory ScienceCenter, which is operated for NASA by the Smithsonian AstrophysicalObservatory.
| Vertical distribution of Galactic disk stars. I. Kinematics and metallicity
Nearly 400 Tycho-2 stars have been observed in a 720 square degree fieldin the direction of the North Galactic Pole with the high resolutionechelle spectrograph ELODIE. Absolute magnitudes, effectivetemperatures, gravities and metallicities have been estimated, as wellas distances and 3D velocities. Most of these stars are clump giants andspan typical distances from 200 pc to 800 pc to the galactic mid-plane.This new sample, free of any kinematical and metallicity bias, is usedto investigate the vertical distribution of disk stars. The old thindisk and thick disk populations are deconvolved from thevelocity-metallicity distribution of the sample and their parameters aredetermined. The thick disk is found to have a moderate rotational lag of-51 +/- 5 km s-1 with respect to the Sun with velocityellipsoid (sigmaU , sigmaV , sigmaW )=(63+/- 6, 39+/- 4, 39+/- 4) km s-1, mean metallicity of[Fe/H] = -0.48 +/- 0.05 and a high local normalization of 15 +/- 7%.Combining this NGP sample with a local sample of giant stars from theHipparcos catalogue, the orientation of the velocity ellipsoid isinvestigated as a function of distance to the plane and metallicity. Wefind no vertex deviation for old stars, consistent with an axisymmetricGalaxy. Paper II is devoted to the dynamical analysis of the sample,puting new constraints on the vertical force perpendicular to thegalactic plane and on the total mass density in the galactic plane.Based on observations made at the Observatoire de Haute Provence(France). Data are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/141
| The positions and flux densities of 74 radio sources from the 3C catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.131..503W&db_key=AST
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| קבוצת-כוכבים: | כלבי ציד |
| התרוממות ימנית: | 14h05m56.09s |
| סירוב: | +34°22'57.6" |
| גודל גלוי: | 8.38 |
| מרחק: | 159.49 פארסק |
| תנועה נכונה: | 16.7 |
| תנועה נכונה: | -70.2 |
| B-T magnitude: | 9.723 |
| V-T magnitude: | 8.491 |
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