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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}
| Optical CCD imaging of the supernova remnant CTA 1
Deep Hα+[NII], [NII], [SII] and [OIII] CCD images have beenobtained from the high galactic latitude supernova remnant CTA 1. Thefilamentary morphology in the light of the [OIII] emission is nowclearly seen in the full field of the remnant. Contrary to the [OIII]morphology, the remnant appears less sharply defined in the light of theHα+[NII], [NII] and [SII]. The morphological differences betweenthe [OIII] and Hα+[NII] emission lines and the presence of anumber of filaments with projected lengths ranging from 0.5 to severalpc suggest an inhomogeneous insterstellar medium. The presence ofincomplete recombination zones is supported by the variations seen inthe [OIII]/H_beta ratio which ranges from 5-20. A low dispersionspectrum taken in the south of CTA 1 indicates surface brightness valuesof Hα, [NII] and [SII] ~13, 14 and 18 in units of 10-17erg s-1 cm-2 arcsec-2} respectively,while the sulfur line ratio suggests an electron density of ~200cm-3. Rough upper limits to the preshock cloud density are ofthe order of {^s}im 1 nuclei cm-3. The strong [OIII] emissionis indicative of shock velocities higher than 100 km s-1while in certain areas of the remnant where the Hα emissiondominates lower velocities are possible. It is the first time thatsignificant optical emission is detected in the northwest area of theremnant, where diffuse radio emission is mainly seen. The small scalefilaments detected there and their flux suggest that we observe shockedmaterial, most likely associated to CTA 1. Three more distinctfilamentary structures are detected in the south-west area, outside ofthe main emission shell. Their lengths range from 1\farcm 5 to 6\farcm5. The spatial locations of the newly detected emission features suggestan angular shock radius of 59 arcmin.
| X-Ray Emission from the Supernova Remnant CTA 1
Abstract image available at:http://adsabs.harvard.edu/abs/1995ApJ...453..284S
| Visual polarization measurements in the Cepheus flare
We present polarization measurements on a stellar sample located in alarge area in Cepheus. The observations were made with the 2-m telescopeat the Pic du Midi (France), around 4350 A and with an accuracy of thepolarization degree of the order of 0.0001. At large scales, we findthat the galactic magnetic field as given by the direction of thepolarization (alignment of the dust) is, roughly speaking, parallel tothe galactic plane in the Cassiopeia cloud, with a scale size of theorder of 100 pc, while it is turned by about 90 in the Cepheus cloud. Atsmall scales, in both the Cepheus and the Cassiopeia clouds, the COcontent has little correlation with the degree of polarization.
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
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Osservazione e dati astrometrici
| Costellazione: | Cassiopea |
| Ascensione retta: | 00h01m35.97s |
| Declinazione: | +72°14'11.8" |
| Magnitudine apparente: | 7.22 |
| Distanza: | 197.239 parsec |
| Moto proprio RA: | -44.5 |
| Moto proprio Dec: | 3.6 |
| B-T magnitude: | 8.695 |
| V-T magnitude: | 7.342 |
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