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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
| Metallicities and activities of southern stars
Aims. We present the results from high-resolution spectroscopicmeasurements to determine metallicities and activities of bright starsin the southern hemisphere. Methods: We measured the iron abundances([Fe/H]'s) and chromospheric emission indices (log h{R}'{HK})of 353 solar-type stars with V = 7.5-9.5. [Fe/H] abundances aredetermined using a custom χ2 fitting procedure within alarge grid of Kurucz model atmospheres. The chromospheric activitieswere determined by measuring the amount of emission in the cores of thestrong Caii HK lines. Results: Our comparison of the metallicity sampleto other [Fe/H] determinations was found to agree at the ±0.05dex level for spectroscopic values and at the ±0.1 dex level forphotometric values. The distribution of chromospheric activities isdescribed by a bimodal distribution, agreeing with the conclusions fromother works. Also an analysis of Maunder minimum status was attempted,and it was found that 6 ± 4 stars in the sample could be in aMaunder minimum phase of their evolution and hence the Sun should onlyspend a few per cent of its main sequence lifetime in Maunder minimum.Based on observations made with the ESO telescopes at the La SillaParanal observatory under programme ID's 076.C-0578(B) and077.C-0192(A). Table 4 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/485/571
| 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
| Metallicity effects on the chromospheric activity-age relation for late-type dwarfs
We show that there is a relationship between the age excess, defined asthe difference between the stellar isochrone and chromospheric ages, andthe metallicity as measured by the index [Fe/H] for late-type dwarfs.The chromospheric age tends to be lower than the isochrone age formetal-poor stars, and the opposite occurs for metal-rich objects. Wesuggest that this could be an effect of neglecting the metallicitydependence of the calibrated chromospheric emission-age relation. Wepropose a correction to account for this dependence. We also investigatethe metallicity distributions of these stars, and show that there aredistinct trends according to the chromospheric activity level. Inactivestars have a metallicity distribution which resembles the metallicitydistribution of solar neighbourhood stars, while active stars appear tobe concentrated in an activity strip on the logR'_HKx[Fe/H] diagram. Weprovide some explanations for these trends, and show that thechromospheric emission-age relation probably has different slopes on thetwo sides of the Vaughan-Preston gap.
| A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
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Osservazione e dati astrometrici
| Costellazione: | Cane Maggiore |
| Ascensione retta: | 07h14m59.76s |
| Declinazione: | -32°48'10.7" |
| Magnitudine apparente: | 8.764 |
| Distanza: | 125 parsec |
| Moto proprio RA: | -36.6 |
| Moto proprio Dec: | 12.2 |
| B-T magnitude: | 9.674 |
| V-T magnitude: | 8.84 |
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