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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}
| Photoelectric Photometry of Herbig Ae/be and Related Stars in the Vilnius Photometric System
A catalog of photoelectric photometry of 62 Herbig Ae/Be and relatedstars in the Vilnius system is presented. It contains stars down to V =12 mag located mainly in the northern hemisphere and observed in theperiod of 1994--1996.
| Dust Extinction and Molecular Cloud Structure: L977
We report results of a near-infrared imaging survey of L977, a darkcloud in Cygnus seen in projection against the plane of the Milky Way.We use measurements of the near-infrared color excess and positions ofthe 1628 brightest stars in our survey to measure directly dustextinction through the cloud following the method described by Lada andcoworkers. We spatially convolve the individual extinction measurementswith a square filter 90" in size to construct a large-scale map ofextinction in the cloud. We integrate over this map to derive a totalmass of M_L977 = (660 +/- 30)(D/500 pc)^2 M_ȯ and, via a comparisonof source counts with predictions of a Galactic model, estimate adistance to L977 of 500 +/- 100 pc. We find a correlation between themeasured dispersion in our extinction determinations and the extinction,which is very similar to that found for the dark cloud IC 5146 in aprevious study. We interpret this as evidence for the presence ofstructure on scales smaller than the 90" resolution of our extinctionmap. To further investigate the structure of the cloud we construct thefrequency distribution of the 1628 individual extinction measurements inthe L977 cloud. The shape of the distribution is similar to that of theIC 5146 cloud. Monte Carlo modeling of this distribution suggests thatin the range 2 mag < A_V < 40 mag (or roughly 1 pc < r < 0.1pc) the material inside L977 is characterized by a density profilerho(r) ~ r^-2. Direct measurement of the radial profile of a portion ofthe cloud confirms this result. At the lower Galactic latitude of L977,we find both the mean and dispersion of the infrared colors of fieldstars to be larger than those observed toward IC 5146. This produces anincrease of about a factor of 2 in the minimum or threshold value ofextinction that can be reliably measured toward L977 with thistechnique. Nevertheless, the accuracy in an extinction map pixel is notsignificantly different toward L977 because of the increased number offield stars at this latitude. We also find an increase in the number ofdetected giant stars at the lower Galactic latitude of the survey byalmost a factor of 2. Most of these excess stars suffer extraneousextinction and are probably red giants seen along the disk of the MilkyWay up to distances of ~15 kpc and reddened by unrelated backgroundmolecular clouds along this direction of the Galaxy. We discuss apossible application of this observable to Galactic structure studies onthe plane of the Galaxy.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT Galactic Plane Survey: Analysis of a low latitude sample area in Cygnus
The analysis of the part of the ROSAT all-sky survey covering thegalactic plane is the scope of a dedicated project called the ROSATGalactic Plane Survey. In order to statistically understand the natureof the ~14,000 sources discovered by ROSAT at |b| <= 20 degrees, anumber of sample areas have been chosen for follow-up opticalidentification. In this paper we present the X-ray and optical materialgathered in a region located in the Cygnus constellation, centered at l= 90 degrees, b = 0 degrees and covering an area of 64.5deg2. A total of 95 and 128 sources are detected with amaximum likelihood larger than 10 and 8 respectively. With a typicalsurvey exposure time of the order of 700 to 900 s the flux completenesslevel is ~0.02 cnts s^{-1} corresponding to ~2 10^{-13} erg cm^{-2}s^{-1}. The position of the sample area allows to investigate the softX-ray content of a rather typical region of the galactic plane. In thispaper we describe the details of the observational procedures and datareduction. For each ROSAT source we list the main X-ray characteristicstogether with those of the proposed optical identification. Whenappropriate, we also show optical spectra and finding charts. The fullanalysis and discussion of these data are presented in a companion paper(\cite[Motch et al. 1997]{ref13}). Tables 2 to 6 are also available inelectronic form at the CDS via anonymous ftp cdsarc.u-strasbg.fr.Figures are only published electronically and are made available athttp://www.ed-phys.fr/Abstract.html.
| The ROSAT galactic plane survey: analysis of a low latitude sample area in Cygnus.
We present the analysis of the point source content of a low galacticlatitude region selected from the ROSAT all-sky survey. The test fieldis centered at l=90deg, b=0deg and has an area of 64.5deg^2^. A total of128 soft X-ray sources are detected above a maximum likelihood of 8.Catalogue searches and optical follow-up observations show that in thisdirection of the galactic plane, 85% of the sources brighter than 0.03PSPC cts/s are identified with active coronae. F-K type stars represent67%(+/-13%) of the stellar identifications and M type stars account for19%(+/-6%). A small but significant number of X-ray sources areassociated with A type stars on the basis of positional coincidence.These results together with those of similar optical campaignsdemonstrate that the soft X-ray population of the Milky Way is largelydominated by active stars. We show that the density and distribution influx and spectral type of the active coronae detected in X-rays areconsistent with the picture drawn from current stellar population modelsand age dependent X-ray luminosity functions. The modelling of thispopulation suggests that most of the stars detected by ROSAT in thisdirection are younger than 1Gyr. This opens the possibility to extractin a novel way large samples of young stars from the ROSAT all-skysurvey. The small number of unidentified sources at low X-ray flux putrather strong constraints on the hypothetical X-ray emission from oldneutron stars accreting from the interstellar medium. Our observationsclearly rule out models which assume no dynamical heating for thispopulation and a total number of N_ns_=10^9^ neutron stars in theGalaxy. If accretion on polar caps is the dominant mode then our upperlimit may imply N_ns_=~10^8^. Among the non coronal identifications arethree white dwarfs, a Seyfert 1 active nucleus, two early type stars andone cataclysmic variable. We also report the discovery of a Me + WDclose binary system with P_orb_=~12h.
| 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.
| Chromospheric activity in G and K giants: the spectroscopic data base
I present high-resolution CCD spectra of CaII H and K emission lines of59 evolved stars of spectral type G and K and luminosity Class III,III-IV, and IV. This includes active stars like RS CVn binaries but alsoactive and inactive single stars. Most of the objects were observed forthe first time and several were discovered to be chromosphericallyactive. Spectra for ten stars of luminosity Class V are also given.
| Chromospheric activity in G and K giants and their rotation-activity relation
We obtained high-resolution CCD spectra of Ca II H and K emission linesof 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS CVn binariesbut also active and inactive single stars. Whenever possible wedetermine absolute emission line surface fluxes and use them,supplemented by previously published fluxes from high-resolutionspectra, to quantify the rotation-activity relation for evolved stars.We find that the Ca II surface fluxes from evolved stars scale linearlywith stellar rotational velocity and that the flux from the cooler starsdepends stronger upon rotation than the flux from the hotter stars, inagreement with previous findings for main-sequence stars. However, largescatter indicates that rotational velocity might not be the onlyrelevant parameter. We also present some evidence for the existence of a'basal' flux for evolved stars that scales approximately with the eightpower of the effective surface temperature.
| On the coronae of rapidly rotating star. V - The other stars
Results of Einstein X-ray observations of 25 stellar systems arepresented. The systems observed include 15 spectroscopic binaries ofwhich eleven were detected; nine were serendipitous detections, three ofwhich may be new RS CVn systems. Coronal activity levels and theirimplications for these stars are discussed.
| A systematic search for members of the Hyades Supercluster. V - The red giants
The membership of bright, red giants in the Hyades Supercluster isdetermined by studying their proper motions and their radial velocities.At least 44 of the giants in the Bright Star Catalogue are found to bemembers of the Supercluster, including the known variables R Hya, Pi'Grum TW Hor, NP Pup, R Lyr, VZ Cam, and AD Cet. The nearest member at 29pc is HR 2715, which is also the oldest at 10 to the 9th yr. Thevariables contain a mixture of modes of pulsation and noperiod-luminosity relation is found. The majority of the members are G8to K0 stars and the lone billion-yr old member is all that is expectedfrom the number of A stars of that age in the Supercluster. Theavailable intermediate-band photometry gives luminosities in reasonableagreement with the astrometric values and, together with DDO photometry,shows consistency in the heavy-element abundance of G- and K-typeSupercluster members.
| 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
| UBV and narrow-band UVBY photometry of bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73...84B&db_key=AST
| Colors of bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1954AJ.....59..228E&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 21h03m26.00s |
| Declinazione: | +50°21'07.0" |
| Magnitudine apparente: | 6.37 |
| Distanza: | 119.048 parsec |
| Moto proprio RA: | 65.4 |
| Moto proprio Dec: | 46.6 |
| B-T magnitude: | 7.615 |
| V-T magnitude: | 6.473 |
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