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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}
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photometry of V 1794 Cygni between 1975 and 1995
Six years of new photometry of V 1794 Cyg is combined with thepreviously published data. These data are processed into two decades ofhomogeneous standard Johnson UBVRI photometry, which contains 1207,1837, 1927, 867 and 75 observations in U, B, V, R and I, respectively.
| Doppler imaging of stellar surface structure. X. The FK Comae-type star HD 199178 = V 1794 Cygni
Doppler imaging is used to derive the surface temperature distributionof the FK Comae star HD 199178 for five observing epochs between 1988and 1997. Our maps are mainly based on Ca i 6439-Ä line profilesand simultaneous and contemporary BV and VI photometry. All images of HD199178 are characterized by a large polar spot and several low-latitudespots with an average surface temperature difference, photosphere minusspots, of 710+/-260(rms) K for the equatorial spots, ~1700 K for thepolar spot, and 1300+/-300(rms) K for the polar-spot appendages. Thelifetime of some of the low-latitude spots was found to be as short asone month or even less. The lifetime of the polar spot and most of itsvery cool appendages must exceed the time of our observations, i.e. 9years or approximately 1000 stellar rotations, and could be as long as12 years since its discovery by Vogt in 1985. Two consecutive Dopplermaps in 1989 show no evidence for differential surface rotation, nor isthere substantial evidence for the existence of active longitudes in anyof our five images. Instead, we suspect that most of the timevariability of the surface features on HD 199178 is short term andpossibly chaotic in origin. We conclude that spot lifetimes estimatedfrom the timing of light-curve minima could lead to grosslyoverestimated lifetimes of individual spots. With the aid of our opticalspectra and the Hipparcos parallax, we redetermine the absolute stellarparameters of HD 199178 and confirm it to be a single G5III-IV star andfind 1.65 M_sun and 11 L_sun with T_eff~ 5450 K, log g=2.5, and solarabundances.
| 1990 and 1991 UBVRI Photometry of HD 199178 = V1794 Cyg
Not Available
| Collected photometric and polarimetric observations of HD 199178
The collected photometric observations of the FK Comae-type star HD199178 extending from 1975 to 1989 are presented. All observations aretransformed to the standard Johnson UBVRI-system. An improved ephemerisis determined from the photometry, and the light curve and color indexcurve fits are derived. The collected polarimetric observations from1981 to 1988 and the second-order Fourier fits of these observations arealso given. A detailed description of the methods used in combining thenew and previously published photometry and polarimetry is given withthe aim of establishing a firm basis for long-term studies of thisobject.
| Photoelectric Photometry of Stars in the Vilnius System in the Area of the North America and Pelican Nebulae
Not Available
| Errata in Magnitudes of Stars in AGK3
Not Available
| Observations of active chromosphere stars
It is pointed out that spectroscopic signatures of stellar chromosphericactivity are readily observable. The present study is concerned with newphotometric and spectroscopic observations of active-chromosphere RSCVn, BY Dra, and FK Com stars. Attention is given to the first resultsof a synoptic monitoring program of many active chromosphere stars.During the time from 1980 to 1982, photometric and spectroscopicobservations of 10 known or suspected active-chromosphere objects weremade. The results regarding the individual stars are discussed. Sevenstars observed with the International Ultraviolet Explorer (IUE) are allspectroscopic binaries.
| Observational stability in AM stars
Differential photoelectric photometry is carried out in metallic-linestars suspected of variability and in the pulsating Am: star HR 8210.The pulsational stability of classical Am stars is confirmed and thehypothesis that the Am phenomenon is the result of diffuse elementseparation is still consistent with the observations. The variability ofHR 8210 is confirmed too. The behavior of this star should beinterpreted as evidence of a multiple-period structure.
| Kinematical data of two samples of late-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27..267G&db_key=AST
| Photometry of V1057 CYG and neighboring stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..379L&db_key=AST
| Narrow-band photometry of late-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..199H&db_key=AST
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Hattyú |
| Rektaszcenzió: | 20h58m55.64s |
| Deklináció: | +44°03'37.6" |
| Vizuális fényesség: | 6.644 |
| Távolság: | 219.298 parszek |
| RA sajátmozgás: | 18.9 |
| Dec sajátmozgás: | 15.7 |
| B-T magnitude: | 8.005 |
| V-T magnitude: | 6.757 |
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INHABITED SKY
