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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}
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| Large and kinematically unbiased samples of G- and K-type stars. V - Evolved stars in the selected areas at + 15-deg declination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..242E&db_key=AST
| Photoelectric radial velocities, Paper XIII - 406 ninth-magnitude K0 stars in the Clube Selected Areas
Radial velocities are given for 406 ninth-magnitude late-type stars. Thestars are grouped in 10 small regions located on a systematic plan atGalactic latitudes of + or - 35 deg. Each star has been observed atleast twice, and the mean velocities are accurate to about less than 1km/s. Thirty spectroscopic binaries have been discovered; orbits havealready been given for 13 of them, and observations of the others arecontinuing.
| Lunar occultation summary. II
Results of a second series of 196 two-color photoelectric lunaroccultation observations made within the interval from May 1972 toDecember 1973 are reported. Each observation has been employed toestimate the minimum magnitude difference between the observed objectand possible undetected companions. The study contains the analyses of143 disappearances and 53 reappearances. Eighteen of these eventsmanifest some degree of multiplicity. Included in the study are 18occultation events for Pleiades members.
| Accuracy of two-dimensional spectral classes derived through DDO photometry.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..832Y&db_key=AST
| Photoelectric radial velocities. IV. 528 7 to 10 mag stars in the +15degree selected areas.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.155....1G&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | סרטן |
| התרוממות ימנית: | 09h17m21.80s |
| סירוב: | +13°04'53.6" |
| גודל גלוי: | 8.423 |
| מרחק: | 228.311 פארסק |
| תנועה נכונה: | 2.2 |
| תנועה נכונה: | -11.4 |
| B-T magnitude: | 9.896 |
| V-T magnitude: | 8.545 |
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INHABITED SKY
