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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
| 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
| Stellar atmospheric parameters for F-G-K stars from low-resolution data: method and application to a sample of proper motion stars
We develop a general method which allows us to derive fundamentalstellar parameters (T_eff_, [M/H]) of F, G, and K dwarfs fromlow-resolution spectra covering the wavelength range 370-780 nm andusing three different grids of model atmosphere flux distributions. Twoextreme cases are explored: (1) broad-band synthetic color indices,which exploit a large fraction of the available wavelength range, but athighly degraded spectral resolution, and (2) synthetic spectrum fitting,which takes full advantage of the available resolution in the data, butwhich is limited to a relatively narrow wavelength interval. We showthat, while in either case the initial model-derived parameter valuesdiffer systematically from published results obtained viahigh-resolution spectroscopy these spectroscopic data can be used toproperly calibrate the models. Thus, as an application, we were able toderive abundances for 40 proper motion stars, selected from Fresneau(1990). Within the systematic biases that could exist, the derivedmetallicity distribution is bimodal, one mode centered on [M/H] = 0.0dex(thin disk) and the other on [M/H] = -0.6dex (thick disk), biasedtowards the thick disk. Furthermore, three low metallicity stars and asuper metal-rich one have been discovered.
| A uvby-like photometric system for the WF/PC of the HST
The possibility of combining four filters of the Hubble Space TelescopeWide Field/Planetary Camera into a uvby-like photometric system isdiscussed. On the basis of earth-based observations with appropriatefilters, such a system consisting of WF/PC filters F 368M, F 413M, F492M, and F 547M was calibrated for the determination of fundamentalparameters of F dwarf stars. A good agreement was found between thisempirical calibration and a theoretical one by Bell (1988). Goodestimates of effective temperatures and metallicities can be obtainedwith this system, while gravity determinations require a UV filter atshorter wavelengths.
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Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 20h30m18.77s |
| Declinazione: | +54°40'51.6" |
| Magnitudine apparente: | 7.457 |
| Distanza: | 52.966 parsec |
| Moto proprio RA: | 98.1 |
| Moto proprio Dec: | 103.9 |
| B-T magnitude: | 8.057 |
| V-T magnitude: | 7.507 |
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