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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 Nature of Overluminous F Stars Observed in a Radial-Velocity Survey
We have conducted a radial-velocity survey of bright (V<9),overluminous, F stars within 80 pc. The criterion of overluminosity isΔMc0=Mc0-MV>=0.5,where MV is the absolute magnitude based on the Hipparcosparallax and Mc0 is the absolute magnitude fromuvby photometry. For F stars, overluminosity at a level ofΔMc0>0.15 has been argued to beindicative of the presence of a bright companion, so many of theoverluminous ``single'' F stars are expected to be, in fact, binarieswith comparably bright components. Therefore, the main goals of thesurvey have been to gain insight into the nature of overluminous F starsand to test specifically the hypothesis of the duplicity of overluminousF stars by searching for previously unrecognized binary stars amongthem. Other goals of this project included the determination, whereverpossible, of the orbits of the binaries discovered as a result of thesurvey and comparing the properties of the binaries with those of thevisually single stars with constant radial velocity. The program listcomprised 111 stars that appear in the Hipparcos catalog as single, plusseven members of multiple systems whose components have individualentries in the catalog.Of the total of 118 stars selected, the radial velocities of 77 havebeen measured with the Cambridge CORAVEL in the present survey. Amongthe remainder, six have not allowed us to determine their radialvelocities because of the weakness or lack of a ``dip'' in theirradial-velocity traces, and one was optically inaccessible to thetelescope. All the rest proved to be sufficiently well known alreadyeither as binary or as constant-radial-velocity (CRV) stars. The surveydiscovered 25 new binary systems, not counting two that were notgenerally known as such but were already under observation by R. F. G.and two that were discovered by Hipparcos to show eclipses but had neverbeen recognized as SBs. With the previously known binaries, there is atotal of 61 definite plus three probable binaries out of a total of 111stars upon which we can adjudicate-a binary fraction of ~58%, justdouble the ~29% found in a sample of randomly selected F stars byNordström et al. (1997). Of the binaries, 52 are SB2 and 12 areSB1. Orbits (some of them still rather preliminary) have been determinedfor the first time for 28 binaries, 21 of which are SB2.Comparison of the CRV stars (a total of 47) with the SB2 binaries hasshown that the two groups have different kinematics. The differenceimplies that on average the CRV stars are 3 to 4 Gyr older than theSB2s, although several of the CRVs appear to be very young. At the sametime the SB2 stars turn out to have about the same kinematics, hence thesame average age, as both binary and normal single F stars from acontrol sample drawn from the Hipparcos catalog. The much older age ofthe bulk of the overluminous CRV F stars may be indicative of anomalousstellar evolution that results in anomalously long main-sequencelifetimes for those stars. The SB1 stars appear to be closer to the CRVsthan to the SB2s and are probably also very old. The properties of the``no-dip'' stars suggest very young age; some of the stars are probablypre-main-sequence (PMS). A few PMS candidates have been identified alsoamong the CRV stars. Thus, overluminous F stars comprising our sampleappear to consist of three distinct groups: mostly young SB2 binarieswith comparably bright components, mostly very old CRV and SB1 stars,and very young no-dip stars.
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:/ /cdsweb.u-strasbg.fr/ cgi-bin/qcat?J/ A+A/394/927
| Mesures de vitesses radiales. VII. Accompagnement AU sol DU programme d'observation DU satellite Hipparcos. Radial velocities. VII. Ground based measurements for Hipparcos.
We publish 734 radial velocities of stars distributed in 28 fields of4x4deg. We continue the PPO series (Fehrenbach et al. 1987; Duflot etal. 1990 and 1992), using the Fehrenbach objective prism method.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
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לינקים קשורים
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | חץ |
| התרוממות ימנית: | 20h11m15.44s |
| סירוב: | +16°51'10.7" |
| גודל גלוי: | 7.569 |
| מרחק: | 74.906 פארסק |
| תנועה נכונה: | 74.8 |
| תנועה נכונה: | -10.4 |
| B-T magnitude: | 8.051 |
| V-T magnitude: | 7.609 |
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