We report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates. Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age-metallicity and age-velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ag

Andersen, J.

Holmberg, J.

Jørgensen, B. R.

Mayor, M.

Nordström, B.

Pont, F.

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CSIRO PUBLISHING 5th Workshop on Galactic Chemodynamicswww.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia, 2004, 21, 129–133The Geneva–Copenhagen Survey of the Solar NeighbourhoodB. Nordström1,2,6, J. Andersen3,4, J. Holmberg3,4, B. R. Jørgensen1,M. Mayor5, and F. Pont 51 Lund Observatory, Box 43, SE 22100 Lund, Sweden2 Niels Bohr Institute for Astronomy, Physics & Geophysics, DK 2100 Copenhagen, Denmark3 Astronomical Observatory, DK 2100 Copenhagen, Denmark4 Nordic Optical Telescope Scientific Association, Apartado 474, ES 38700 Santa Cruz deLa Palma, Spain5 Observatoire de Genève, CH 1290 Sauverny, Switzerland6 E-mail: birgitta@astro.lu.seReceived 2003 November 21, accepted 2004 February 6Abstract: We report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new,accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary starsin the sample. Isochrone ages have been determined whenever reliable results are possible, with particularattention to realistic error estimates.Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicitydistribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. Weconfirm the lack of metal-poor G-dwarfs relative to classical model predictions (the ‘G-dwarf problem’),the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of thekinematic signature of the thick disk ∼10 Gyr ago.Keywords: Galaxy: solar neighbourhood — Galaxy: disk — Galaxy: kinematics and dynamics — Galaxy:evolution1 MotivationThe solar neighbourhood affords the most basic tests ofmodels of the Galactic disk: the sample volume around theSun provides a first estimate of the stellar mass density ofthe disk in the Galactic plane. The distribution in age ofthese stars is our record of the star formation history of thedisk. Similarly, their chemical abundances as functions ofage are the fossil record of the chemical enrichment historyof the disk. Finally, the space motions and Galactic orbitsof the stars as functions of age are clues to the paralleldynamical evolution of the Galaxy and diagnostics of itsmix of stellar populations from different regions of thedisk (see, for example, the recent review by Freeman &Bland-Hawthorn 2002).F- and G-type dwarf stars are excellent tracers of thishistory. They are both numerous and sufficiently long-lived to survive from the time of formation of the disk;their convective atmospheres reflect their initial chemi-cal composition; and ages can be estimated for at leastthe more evolved stars by comparison with stellar evolu-tion models. Photometry in the Strömgren uvbyβ systemis an efficient means to derive intrinsic stellar proper-ties from observation (Strömgren 1963, 1987). RecentGalactic studies based mainly on uvbyβ photometry are,for example, Jørgensen (2000), Feltzing et al. (2001), andHolmberg (2001).Our key new contribution consists of accurate, multipleradial velocity observations for an all-sky, magnitude-limited, and kinematically unbiased sample of over 14 000nearby F- and G-stars. Because this data set is unlikelyto be superseded until the results of the Gaia mis-sion (Perryman et al. 2001) and/or the RAVE program(Steinmetz 2003) appear, we have also redetermined Teff ,Mv, and [Fe/H] as well as ages and Galactic orbits forall stars in the sample with adequate data. The programwas briefly outlined at an earlier meeting in this series(Nordström et al. 1996); the complete catalogue with afull discussion will appear elsewhere (Nordström et al.2004).The much-cited paper by Edvardsson et al. (1993)studied the detailed chemistry of a subset of the sam-ple discussed here. That paper shed much new light onthe detailed nucleosynthesis history of the disk, but suf-fered from strong selection effects which our sample wasdesigned to overcome. Thus, the two studies address thesame subject from complementary angles.© Astronomical Society of Australia 2004 10.1071/AS04013 1323-3580/04/02129https:/www.cambridge.org/core/terms. https://doi.org/10.1071/AS04013Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 15:58:01, subject to the Cambridge Core terms of use, available at130 B. Nordström et al.Figure 1 Distribution on the sky of the 14 139 stars with completekinematical data.Figure 2 Distribution in apparent magnitude for the full sample(full line), and for stars with radial velocity data (dotted line). Thedashed curve shows the relation for a uniform, volume-completesample.2 Sample DefinitionThe stars were selected from the uvbyβ catalogues byOlsen (1983, 1993, 1994a, 1994b) to form a magnitude-limited, kinematically unbiased, all-sky sample of F- andG-dwarfs which would at the same time be volume-complete to a distance of ∼40 pc. For details of theselection procedures see Nordström et al. (2004)The distribution on the sky of the sample stars withcomplete kinematical data is shown in Figure 1, in equa-torial coordinates and in an equi-area projection. Note theconcentration of stars in the Hyades — observed with spe-cial care for calibration purposes — and the addition of thelatest-type dwarfs (to K2V) south of δ=−26◦.Apart fromthese features, the sample is very uniformly distributed.The distributions in (apparent) V magnitude for thewhole sample and for those stars with complete chemicaland kinematical data are shown in Figure 2. The mag-nitude completeness of the sample can be estimated bycomparison with the distribution expected for a uniformvolume density of stars. The full sample starts to becomeincomplete near V = 7.6.3 Observational DataThis section summarises the observational data used tocompute the astrophysical and kinematical parametersfor our program stars. Our new radial velocity observa-tions are described in detail; the Strömgren uvbyβ photo-metry is from the catalogues by Olsen (1983, 1993, 1994a,1994b). For other data, the relevant sources are givenbelow.3.1 Radial VelocitiesMost of the new radial velocity data were obtained with theCORAVEL photoelectric cross-correlation spectrometers(Baranne et al. 1979; Mayor 1985), operated at the Swiss1-m telescope at Observatoire de Haute-Provence, France,and the Danish 1.5-m telescope at ESO, La Silla. Thetwo CORAVELs thus cover the entire sky, and their fixed,late-type cross-correlation templates efficiently match thespectra of the large majority of our program stars.Two or more observations have been made for almostall stars over a substantial time base, typically 500–1000days, but occasionally more than a decade. This allows usto define more reliable mean velocities and identify mostof the spectroscopic binaries which, if unrecognised, yieldmisleading astrophysical parameters from the observedmagnitudes and colour indices. Between the two tele-scopes, a total of 62 993 CORAVEL observations havebeen made of 12 941 of the program stars discussed inthis paper. Additional observations of fast-rotating starswere made at the Center for Astrophysics (Nordströmet al. 1997).The mean radial velocities are very accurate; the distri-bution of their mean errors is shown in Figure 3. As willbe seen, mean errors are typically ∼0.25 km s−1 and onlyrarely exceed 1 km s−1. Stars are labelled as binaries whentheir velocity is variable at the 99% confidence level.3.2 ParallaxesGood distances are crucial in order to compute accu-rate absolute magnitudes, distances, and space motionsfor the program stars. Hipparcos parallaxes, generally ofvery good accuracy, are available for the majority of theserelatively nearby stars (ESA 1997).3.3 Proper MotionsAccurate proper motions are available for the most of thestars from the Tycho-2 catalogue (Høg et al. 2000). Thiscatalogue is constructed by combining the star-mappermeasurements of Hipparcos with the Astrographic Cata-logue, based on measurements in the Carte du Ciel andhttps:/www.cambridge.org/core/terms. https://doi.org/10.1071/AS04013Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 15:58:01, subject to the Cambridge Core terms of use, available atThe Geneva–Copenhagen Survey of the Solar Neighbourhood 131Figure 3 The distribution of the mean errors of the mean radialvelocities in the catalogue.other ground-based catalogues and extending the timebase to nearly a century. The mean propagated error inspace motion from proper-motion errors alone is only0.7 km s−1.4 Derived Astrophysical ParametersThe astrophysical data needed to discuss the evolutionaryhistory of the solar neighbourhood are derived from theobservations using the calibrations discussed below.4.1 Metal AbundancesThe accurate determination of metallicities for F- and G-dwarfs is one of the strengths of the Strömgren uvbyβsystem. Among the available calibrations, we have usedthat by Schuster & Nissen (1989) for the majority of thestars. Approximately 600 stars in our sample are cov-ered by both the F- and G-star calibrations of Schuster &Nissen (1989), and the mean difference in [Fe/H] is0.06 dex with a dispersion around the mean of only 0.07.We have further compared these photometric metallici-ties with the homogeneous spectroscopic values for F-and G-stars by Edvardsson et al. (1993) and Chen et al.(2000). The agreement is excellent, with mean differencesof only 0.02 and 0.00 dex and dispersions around the meanof 0.08 and 0.11, respectively.An improved calibration hasbeen derived for stars outside the range of validity of therelations by Schuster & Nissen (1989).5 Effective TemperaturesEffective temperatures for all stars have been determinedfrom the reddening-corrected uvby indices, using thecalibration of Alonso et al. (1996) which is based on theinfrared flux method. Tests show these temperatures tobe accurate to about ±100 K.Figure 4 MV versus log Teff for all stars.5.1 Distances and Absolute MagnitudesAs most of our program stars have excellent trigonometricparallaxes from Hipparcos, we have primarily determinedtheir distances from these parallaxes. The distances areused to compute the tangential space motion componentsfrom the proper motions, and the absolute magnitudesused in the determination of ages and masses.From the best Hipparcos parallaxes we find thatthe photometric distance determinations are accurate to∼13%. Accordingly, we use the Hipparcos distance if theparallax is available and accurate to 13% or better; oth-erwise we adopt the photometric distance, correcting forinterstellar extinction when known. A typical error in MVfor our dwarf stars is therefore 0.26 magnitudes or better.The resulting HR diagram is shown in Figure 4.5.2 AgesIndividual stellar ages are crucial in order to place theobserved chemical and kinematical properties of the starsin an evolutionary context. Because of their importance,we have devoted a great deal of effort to determining theages, and in particular their errors, with far greater sophis-tication than, for example, Edvardsson et al. (1993), takingboth calibration errors and a range of statistical biases intoaccount. The details are beyond the scope of this paper,but are given in Nordström et al. (2004) and Jørgensen &Lindegren (in preparation); at the time of writing, thesecomputations are still in progress.5.3 Space VelocitiesSpace velocities have been computed for all the stars fromtheir distances, proper motions, and mean radial velocities.The (U, V,W) components are defined in a right-handedGalactic system with U pointing towards the Galactic cen-tre, V in the direction of rotation, and W towards the northGalactic pole. No correction for the solar motion has beenhttps:/www.cambridge.org/core/terms. https://doi.org/10.1071/AS04013Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 15:58:01, subject to the Cambridge Core terms of use, available at132 B. Nordström et al.Figure 5 U–V, U–W, and V–W diagrams for all stars in the sample.made. Figure 5 shows the distributions of all the (U, V,W)velocities in the sample.Average errors in each componentare ∼1.5 km s−1.5.4 Galactic OrbitsFrom the positions and space motion vectors of the pro-gram stars we can integrate their orbits back in time andestimate their average orbital parameters. The correlationof such Galactic orbits with the chemical characteristicsand ages of the stars may yield valuable new insight; see,for example, Edvardsson et al. (1993).The observed space motions were corrected for asolar motion of (10.0, 5.2, 7.2) km s−1 (Dehnen & Binney1998). For the orbit integrations we used the potential ofFlynn et al. (1996), adopting a solar Galactocentric dis-tance of 8 kpc, a circular rotation speed of 220 km s−1,disk surface density 52 M pc−2, and disk volume den-sity 0.10 M pc−3 (see Reid et al. 1999; Backer & Sramek1999; Flynn & Fuchs 1994; Holmberg & Flynn 2000).6 DiscussionOur new data set allows us to thoroughly re-evaluatemany of the global properties of the solar neighbourhoodand the Galactic disk. An in-depth analysis will requiredetailed simulations of the predictions of various compet-ing models, subjecting the simulated stellar populationsto the same selection criteria as the observed samples andcomparing the results with the real data set. Such simula-tions will be the subject of future papers, but are beyondthe scope of the present short contribution. Here we justillustrate a few of the new insights that can be expected.The U–W and V–W diagrams in Figure 5 show a smoothdistribution, the Hyades being the only clearly discerniblestructure. The U–V diagram, on the other hand, showsabundant structure in addition to the Hyades, with fourcurved or tilted bands of stars aligned along approximatelyconstant V velocity. These structures have velocitiesresembling classic moving groups or stellar streams andare usually named (top to bottom): Sirius–UMa, ComaBerenices (or local), Hyades–Pleiades, and Hercules, thelatter structure being also known as the U anomaly(Dehnen 1998; Skuljan et al. 1999). Because these struc-tures do not consist only of young stars, they cannot befully described as the resolved remnants of broken-up sys-tems such as classic moving groups, but could be dueto kinematic focussing from non-axisymmetric structuresof the Galaxy, such as spiral arms or the bar. Our dataalso allow further searches for dynamical substructureresulting, for example, from past merger events (Helmiet al. 2003).Among the classical-type analyses, the ‘G-dwarf prob-lem’has been revisited by Jørgensen (2000), using an earlyversion of the present data. The basic result is that, farfrom being eliminated by newly discovered, slow-moving,metal-poor stars, the deficit of metal-poor G-dwarfs rel-ative to the predictions of closed-box models is twice aslarge as before. Obviously, metal-poor stars were in factover-represented in earlier, kinematically biased samples.We defer the discussion of the age–metallicity andage–velocity relations until the last details of our agedeterminations have been settled, as the ages of the veryoldest stars depend very sensitively on such details. Butour preliminary findings are consistent with those byFeltzing et al. (2001), Edvardsson et al. (1993) —and as early as Strömgren (1963!) — that there is nohttps:/www.cambridge.org/core/terms. https://doi.org/10.1071/AS04013Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 15:58:01, subject to the Cambridge Core terms of use, available atThe Geneva–Copenhagen Survey of the Solar Neighbourhood 133clear-cut dependence of metallicity on age for at least thethin disk, while a large, significant scatter exists at all ages.And as shown earlier (Nordström et al. 1999), diffusion ofthe Galactic orbits of the stars is an unlikely explanation ofthis situation. Clearly, even the solar neighbourhood is amuch more complicated and interesting subject than everbefore.Looking ahead a decade from now, Gaia (Perrymanet al. 2001) and RAVE (Steinmetz 2003) should providethe next quantum leap in our knowledge of the Galaxy.The present material should remain useful, not only forstudying our Galaxy in the meantime, but also when opti-mising the observing and data reduction strategies of thoseprojects.AcknowledgementsThis paper rests on very large amounts of observing timeand travel at the Danish 1.5-m telescope at ESO, LaSilla, Chile, and the Swiss 1-m telescope at Observatoirede Haute-Provence, France, granted over many years byESO and the Danish Board for Astronomical Research(to B.N. and J.A.). Several colleagues have made manyobservations and other essential contributions to this work.Substantial financial support from the Carlsberg Founda-tion (to B.N., J.A., and J.H.), the Danish Natural ScienceResearch Council (to B.N. and J.A.), the Fonds NationalSuisse pour la Recherche Scientifique (to M.M. and F.P.),the Smithsonian Institution (to B.N. and J.A.), the SwedishResearch Council and the Nordic Academy for AdvancedStudy (to B.N.), and the Council of the Nordic Opti-cal Telescope Scientific Association (to J.H. and J.A.) isgratefully acknowledged.ReferencesAlonso, A., Arribas, S., & Martínez-Roger, C. 1996, A&A, 313, 873Backer, D. C., & Sramek, R. A. 1999, ApJ, 524, 805Baranne, A., Mayor, M., & Poncet, J.-L. 1979, VA, 23, 279Chen, Y. Q., Nissen, P. E., Zhao, G., Zhang, H. W., & Benono, T.2000, A&AS, 141, 491Dehnen, W. 1998, AJ, 115, 2384Dehnen, W., & Binney, J. J. 1998, MNRAS, 298, 387Edvardsson, B., Andersen, J., Gustafsson, B., Lambert, D. L.,Nissen, P. 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The Geneva-Copenhagen Survey of the Solar Neighbourhood

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