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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
| Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295*
We have discovered both intermediate-order gravity mode and low-orderpressure mode pulsation in the same star, HD 209295. It is thereforeboth a γ Doradus and a δ Scuti star, which makes it thefirst pulsating star to be a member of two classes. The analysis of our128h of multisite spectroscopic observations carried out over twoseasons reveals that the star is a single-lined spectroscopic binarywith an orbital period of 3.10575+/-0.00010d and an eccentricity of0.352+/-0.011. Only weak pulsational signals are found in both theradial velocity and line-profile variations, but we have succeeded inshowing that the two highest-amplitude γ Doradus pulsation modesare consistent with l=1 and |m|=1. These two modes dominated our 280h ofBVIC multisite photometry, also obtained over two seasons. Wedetected altogether ten frequencies in the light variations, one in theδ Scuti regime and nine in the γ Doradus domain. Five of theγ Doradus frequencies are exact integer multiples of the orbitalfrequency. This observation leads us to suspect they are tidallyexcited. Attempts to identify modes from the multicolour photometryfailed. We performed model calculations and a stability analysis of thepulsations. The frequency range in which δ Scuti modes are excitedagrees well with observations. However, our models do not showexcitation of γ Doradus pulsations, although the damping issmaller in the observed range. We also investigated tidal excitation ofγ Doradus modes. Some of the observed harmonics of the orbitalperiod were found to be unstable. The observed orbital harmonics whichare stable in the models can be understood as linear combinations of theunstable modes. We could not detect the secondary component of thesystem in infrared photometry, suggesting that it may not be amain-sequence star. Archival data of this star show that it has a strongultraviolet (UV) excess, the origin of which is not known. The orbit ofthe primary is consistent with a secondary mass ofM>1.04Msolar, which is indicative of a neutron star,although a white dwarf companion is not ruled out.
| 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
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
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| Takýmyýldýz: | Hintli |
| Sað Açýklýk: | 22h08m16.69s |
| Yükselim: | -63°30'18.5" |
| Görünürdeki Parlaklýk: | 7.708 |
| Uzaklýk: | 96.154 parsek |
| özdevim Sað Açýklýk: | 9.8 |
| özdevim Yükselim: | -13.4 |
| B-T magnitude: | 8.192 |
| V-T magnitude: | 7.748 |
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