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The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are 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/418/989
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| The ASCA Medium Sensitivity Survey (the GIS Catalog Project): Source Catalog
We present the first X-ray source catalog of the ASCA Medium SensitivitySurvey (AMSS, or the GIS catalog project), constructed from data atGalactic latitudes b>10deg observed between 1993 May and 1996December. The catalog utilizes 368 combined fields and contains 1343sources with the detection significance above 5 σ either in thesurvey bands of 0.7-7 keV, 2-10 keV, or 0.7-2 keV, including targetsources. For each source, the ASCA source name, position, a 90% errorradius, count rates in the three bands, detection significances, fluxes,and a hardness ratio are provided. With extensive simulations, wecarefully evaluate the data quality of the catalog. Results fromcross-correlation with other existing catalogs are briefly summarized.
| HIPPARCOS distances of X-ray selected stars: implications on their nature as stellar population.
We present the parallaxes, measured by Hipparcos, for a sample of X-rayselected stars. The stars belong to the stellar sample of the EinsteinExtended Medium Sensitivity Survey. They are all at galactic latitude|b|>20deg, and are generally far away from known star formingregions. Several of these stars show lithium abundance and activitylevel typical of very young stars with ages comparable to that of thePleiades. We show that the majority of our sample stars are on the mainsequence, with only =~20% being giants. We do not find a significantpresence of pre-main sequence stars in our sample, notwithstanding thefact that some of our stars have a considerable lithium abundance,showing that the stars observed are most likely young and activemain-sequence objects.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Einstein Extended Medium-Sensitivity Survey Second Epoch: Results for the Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..701F&db_key=AST
| Lithium, X-ray activity and rotation in an X-ray selected sample of solar-type stars
We present an analysis of the connection between X-ray activity level,photospheric abundance of lithium and surface rotation in late typeactive main sequence stars (G and K), using the ratio between opticaland X-ray luminosity fx/fv as an uniform activity indicator. We performthis analysis for a sample of X-ray selected sources from Einstein-basedsurveys compared to stars from the Pleiades open cluster and to a sampleof active binary stars. We show that these parameters show differentdegrees of statistical correlation in the three samples. In particular,the Pleiades sample shows a significant correlation between all threequantities, while in the X-ray selected sample lithium and rotation aresignificantly correlated with each other but neither is correlated withthe activity level. No correlation is evident for the three quantitiesstudied in the active binary sample. We show how the behavior of theX-ray selected sample can be used to discriminate among differenthypothesis about the nature of the so-called `yellow star excess'observed in X-ray flux-limited surveys, showing that this is composed bya population of young, near Zero-Age Main Sequence (ZAMS) stars withcharacteristics similar to the Pleiades.
| A Search for Yellow Young Disk Population Stars among EMSS Stellar X-Ray Sources by Means of Lithium Abundance Determination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...277..428F&db_key=AST
| The Einstein Observatory Extended Medium-Sensitivity Survey. II - The optical identifications
The optical identifications are presented of the Einstein ExtendedMedium-Sensitivity Survey (EMSS), including the methodology used tooptically identify the EMSS sources and the uncertainties involved withthat process. The optical properties of the classes of X-ray, optical,and radio data for each of the identified and, as yet, unidentifiedsources of the survey are described. A new class of X-ray emitters,cooling flow galaxies, is proposed. The criteria used to determinewhether the proposed optical counterpart to the X-ray source is aplausible identification are described. Plausibility is based on theoptical classification of the counterpart, e.g., AGN, cluster, G star,and the X-ray-to-optical flux ratios previously observed for theseclasses of X-ray emitters. Two independent schemes of opticalclassification of the counterparts are used to check the plausibility ofthese identifications; one is based on moderate-resolution opticalspectroscopy, and the other, on inferred X-ray luminosity and theoverall energy distribution.
| The Einstein Observatory Extended Medium-Sensitivity Survey. I - X-ray data and analysis
This paper presents the results of the analysis of the X-ray data andthe optical identification for the Einstein Observatory ExtendedMedium-Sensitivity Survey (EMSS). The survey consists of 835serendipitous sources detected at or above 4 times the rms level in 1435imaging proportional counter fields with centers located away from theGalactic plane. Their limiting sensitivities are about (5-300) x 10 tothe -14th ergs/sq cm sec in the 0.3-3.5-keV energy band. A total area of778 square deg of the high-Galactic-latitude sky has been covered. Thedata have been analyzed using the REV1 processing system, which takesinto account the nonuniformities of the detector. The resulting EMSScatalog of X-ray sources is a flux-limited and homogeneous sample ofastronomical objects that can be used for statistical studies.
| The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection
An X-ray-selected sample of 128 late-type (F-M) stars analyzed. Thesestars were identified as optical counterparts to serendipitous X-raydetections made by the Einstein Observatory Extended Medium SensitivitySurvey. Once identified as X-ray sources, the sample was followed up byan extensive program of optical observations, including high-resolutionand low-resolution spectroscopy and photometry. Spectral types,luminosity classes, distances, X-ray luminosities, projected rotationrates (v sin i), radial velocities, and binary status have beendetermined for the sample.
| The positions and flux densities of 74 radio sources from the 3C catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.131..503W&db_key=AST
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Ökörhajcsár |
| Rektaszcenzió: | 14h43m22.33s |
| Deklináció: | +51°55'05.2" |
| Vizuális fényesség: | 8.236 |
| Távolság: | 48.1 parszek |
| RA sajátmozgás: | -60.7 |
| Dec sajátmozgás: | 120.1 |
| B-T magnitude: | 9.008 |
| V-T magnitude: | 8.3 |
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