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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}
| A multi-wavelength study of the oxygen-rich AGB star CIT 3: Bispectrum speckle interferometry and dust-shell modelling
CIT 3 is an oxygen-rich long-period variable evolving along theAsymptotic Giant Branch and is one of the most extreme infrared AGBobjects. Due to substantial mass loss it is surrounded by an opticallythick dust shell which absorbs almost all visible light radiated by thestar and finally re-emits it in the infrared regime. We present thefirst near infrared bispectrum speckle-interferometry observations ofCIT 3 in the J-, H-, and K'-band. The J-, H-, andK'-band resolution is 48 mas, 56 mas, and 73 mas, resp. Theinterferograms were obtained with the Russian 6 m telescope at theSpecial Astrophysical Observatory. While CIT 3 appears almostspherically symmetric in the H- and K'-band it is clearlyelongated in the J-band along a symmetry axis of position angle -28degr. Two structures can be identified: a compact elliptical core and afainter north-western fan-like structure. The eccentricity of theelliptical core, given by the ratio of minor to major axis, isapproximately varepsilon =123 mas/154 mas = 0.8. The full opening angleof the fan amounts to approximately 40degr . Extensive radiativetransfer calculations have been carried out and confronted with theobservations taking into account the spectral energy distributionranging from 1 mu m to 1 mm, our near-infrared visibility functions at1.24 mu m, 1.65 mu m and 2.12 mu m, as well as 11 mu m ISIinterferometry. The best model found to match the observations refers toa cool central star with Teff=2250 K which is surrounded byan optically thick dust shell with tau (0.55 mum ) = 30. The models givea central-star diameter of Theta *=10.9 mas and an inner dustshell diameter of Theta 1=71.9 mas being in line with lunaroccultation observations. The inner rim of the dust-shell is located atr1= 6.6 R* and has a temperature ofT1=900 K. The grain sizes were found to comply with agrain-size distribution according to Mathis et al. (\cite{MRN77}) withn(a) ~ a-3.5, and 0.005 mu m <= a <= 0.25 mu m. Uniformoutflow models, i.e. density distributions with rho ~ 1/r2,turned out to underestimate the flux beyond 20 mu m. A two-componentmodel existing of an inner uniform-outflow shell region (rho ~1/r2) and an outer region where the density declines moreshallow as rho ~ 1/r1.5 proved to remove this flux deficiencyand to give the best overall match of the observations. The transitionbetween both density distributions is at r2 = 20.5r1= 135.7 R* where the dust-shell temperature hasdropped to T2 = 163 K. Provided the outflow velocity keptconstant, the more shallow density distribution in the outer shellindicates that mass-loss has decreased with time in the past of CIT 3.Adopting vexp=20 km s-1, the termination of thatmass-loss decrease and the begin of the uniform-outflow phase took place87 yr ago. The present-day mass-loss rate can be determined to be dot M= (1.3-2.1) x 10-5 Msun/yr for d=500-800 pc.
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| GPM1 - a catalog of absolute proper motions of stars with respect to galaxies
The description of the first version of the General Compiled Catalogueof Absolute Proper Motions (GPM1) for a sample of HIPPARCOS stars,derived with respect to galaxies within the plan called Catalogue ofFaint Stars (KSZ, Deutch 1952), is presented. The principal aim of theGPM1 construction was to provide absolute proper motions of stars todetermine the rotation of the HIPPARCOS system. The GPM1 cataloguecontains 977 HIPPARCOS Input Catalogue stars with V magnitudes $5^m -11^m in 180 fields north of -25 degrees of declination. The accuracy ofthe proper motions is 8 mas/yr (milliarcseconds per year). Comparison ofproper motions of GPM1 with those of the PPM and ACRS was performed andanalyzed with respect to systematic errors caused by spurious rotationof the FK5 system. The standard errors show that the rotation may bedetermined with an accuracy better than 1 mas/yr. Catalog is onlyavailable in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr or ftp 130.79.128.5.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Halak |
| Rektaszcenzió: | 01h21m44.06s |
| Deklináció: | +09°42'21.6" |
| Vizuális fényesség: | 8.115 |
| Távolság: | 276.243 parszek |
| RA sajátmozgás: | 20.7 |
| Dec sajátmozgás: | -6.1 |
| B-T magnitude: | 10.096 |
| V-T magnitude: | 8.279 |
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