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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
| Wind properties of Wolf-Rayet stars at low metallicity: Sk 41 (SMC)
The stellar properties of Sk 41 (AB4, WN5h), the only known singleWolf-Rayet star in the SMC, are derived from ultraviolet (IUE), optical(AAT) and near-IR (NTT) spectroscopy. Contrary to expectations for lowmetal environments, the stellar properties of Sk 41 are typical ofequivalent WN stars in the Galaxy and LMC, with T* ~ 42kK,log(L/Lsun)=5.7, vinfty =1300 km s-1,H/He ~ 2 by number, and dot {M}/sqrt {f}=3x10-5Msunyr-1, where f is the volume filling factor.The stellar luminosity of Sk 41 is 50% below the minimum value predictedby single star evolutionary models at the metallicity of the SMC,suggesting a deficiency in present evolutionary models at lowmetallicity. Emission line luminosities of He II lambda 4686 and C IVlambda lambda 5801-12 in SMC WR stars are not systematically lower thantheir Galactic and LMC counterparts. From 43 late-type and 59 early-typeWN stars, log Llambda HeII= 36.0 ergs-1 and 35.8 erg s-1, respectively, while logLlambdaCIV =36.5 erg s-1. from 25early-type WC stars. This new calibration has application in deriving WRpopulations in young starburst galaxies. Synthetic WN models arecalculated with identical parameters except that metal abundances arevaried. Following the Smith et al. WN classification scheme, CNOequilibrium models reveal that earlier spectral types are predicted atlower metallicity, i.e. WN3-4 at 0.04Zsun versus WN6 at1.0Zsun. This provides an explanation for the trend towardsearlier WN spectral types at low metallicity. Based, in part, onobservations collected at the European Southern Observatory, La Silla,Chile (Proposal No. 61.D--0680 and 63.H--0683)
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| 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
| Estimation of stellar intrinsic colours, distances and colour excesses based on the Stromgren and H-beta photometry of 804 B, A, and F stars in 10 Selected Areas
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989A&AS...78..105F&db_key=AST
| Four-colour UVBY and H-beta photometry of all A and F stars brighter than MPG of about 11.0 mag in 4 Selected Areas at intermediate galactic latitudes
As a second part of an investigation of the distribution of interstellardust in the solar vicinity, uvby-beta photometry has been obtained for260 stars of spectral types A and F, and brighter than mpg of11.0 mag in four Kapteyn's Selected Areas. The observed areas are: SA95, SA 120, SA 168, and SA 200. They are centered at intermediategalactic latitudes, in the range from b of about -38 deg to -42 deg.From the observed (b-y) versus beta diagrams it can be seen that starsin SA 95 are strongly affected by reddening, while the other areas showvery little absorption.
| Interstellar polarization from observations of A and F stars in high and intermediate galactic latitudes, and from stars in the Mathewson and Ford polarization catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986A&AS...64..487K&db_key=AST
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| Takýmyýldýz: | Kucuk Su yilani |
| Sað Açýklýk: | 00h23m16.14s |
| Yükselim: | -76°43'27.1" |
| Görünürdeki Parlaklýk: | 8.085 |
| Uzaklýk: | 176.056 parsek |
| özdevim Sað Açýklýk: | 25 |
| özdevim Yükselim: | 8.5 |
| B-T magnitude: | 8.599 |
| V-T magnitude: | 8.128 |
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