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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}
| Spectroscopic and photometric observations of the short-period RS CVn-type star WY Cnc
High-resolution spectroscopic observations around the H\alphaline and BVRI photometry of the eclipsing short-period RS CVn star WYCnc are presented. The solutions of our radial velocity curves and lightcurves yielded the following values for masses and radii of thecomponents: M1=0.84 Mȯ, M2=0.46Mȯ, R1=1.06 Rȯ,R2= 0.65 Rȯ. The measured rotationalbroadenings of the spectral lines correspond to equatorial velocitiesV1=78 km s-1 and V2=49 kms-1. The distortions of our multicolor light curve of WY Cncwere reproduced by two cool spots on the primary star. An increase ofthe out-of-eclipse brightness by 0.1 mag in February 2001 was detected.Our spectra show Hα line in emission from the secondarystar. The chromospheric activity appeared also in the observed emissioncores of the CaII H and K lines as well as the CaI 6494 line.Based on spectral observations collected at the National AstronomicalObservatory at Rozhen, research was supported in part by the NATOLinkage grant No. PST.CLG.978810 and grant No. 1/2002 of the ShoumenUniversity
| A Decade of Starspot Activity on the Eclipsing Short-period RS Canum Venaticorum Star WY Cancri: 1988-1997
We present optical photometry of the short-period eclipsing RS CVnsystem WY Cancri for the years 1988-1997. For each light curve, we modelthe distortion waves in order to study the behavior of starspots in thissystem. After removing the spot effects from the light curves, we modelthe cleaned data to obtain system parameters. We also note changes inthe luminosity of the primary star that are not explained by the spotvariation.
| Photoelectric Minima of Four RS CVn Type Binary Systems: RT And, SV Cam, WY Cnc, and Z Her
Not Available
| 1988 and 1989 BV Photometry of WY Cnc
Not Available
| 1989 V and K-Band Photometry of WY Cnc
Not Available
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