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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}
| 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.
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| Absolute spectrophotometric investigation of a group of F, G, and K stars in the UV and visible ranges.
Results of the absolute spectrophotometry of 21 F, G, and K stars,obtained via space and ground observations, are presented. The absoluteenergy distribution for these stars in the 2300-6600 A region wasobtained, and results are compared with Kuruch's theoretical models.
| Photometric Data for the Bright Stars
Not Available
| A phenomenological interpretation of stellar chromospheres
An attempt is made to develop a phenomenological interpretation ofstellar chromospheres. The following problems are examined: observedemission powers of 'magnesium' chromospheres on stars based on theultraviolet doublet, 2800 Mg II, observations; dependence ofchromosphere emission on spectral and luminosity classes; stellarchromospheres as an accidental event; chromospheres of stars-componentsof binary systems; stars with the chromospheres of solar type (S) andnonsolar (NS) type; distribution of stars by means of the type of theirchromosphere on luminosity class; stars with superpower magnesiumemission; emission measures for both the 'magnesium' and 'calcium'chromospheres' interrelation between chromosphere, transition zone andcorona; chromospheric activity and rotation of stars; possibility of theexistence of chromospheres on hot stars; phenomenological picture ofstellar chromospheres; stars without the line 2800 Mg II, in emission orin absorption; syndrome of red giant HD 4174. At the end, the problem ofheating of stellar chromospheres is discussed.
| Space and ground-based spectrophotometric observations of a group of stars of the classes F, G, and K
Not Available
| Behavior of lambda 2800 Mg II in stellar spectra
The results of measurements of the equivalent widths of the resonancedoublet of ionized magnesium lambda 2800 Mg II in the spectra of 51relatively faint stars, up to 10m, of the spectral classes B1-K5 arepresented. The observed material has been obtained by means of the spaceobservatory 'Orion 2'. Some regularities in the behavior of lambda 2800Mg II in stellar spectra have been revealed: wide and deep depression ofthe continuous spectra at 2800 A in F-G type stars; the presence of thedoublet lambda 2800 Mg II in the form of weak emission in the spectra ofcold stars (K2-K5); the presence both of the multiplet lambda 3080 Ti IIand the doublet lambda 2800 Mg II simultaneously either in emission - inthe late-type stars - or in absorption in earlier types; the existenceof combined profiles of lambda 2800 Mg II, i.e., a wide absorption linewith a weak emission in the center, in stars of the transitional class(G5-K0), etc. A well-defined empirical relationship between theequivalent width of lambda 2800 Mg II and the spectral class of the starhas been established.
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| Csillagkép: | Szekeres |
| Rektaszcenzió: | 05h20m02.30s |
| Deklináció: | +44°25'32.0" |
| Vizuális fényesség: | 6.62 |
| Távolság: | 290.698 parszek |
| RA sajátmozgás: | 0.7 |
| Dec sajátmozgás: | -19 |
| B-T magnitude: | 8.232 |
| V-T magnitude: | 6.634 |
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