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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
| Photometry of the 1991 Superoutburst of EF Pegasi: Super-Quasi-Periodic Oscillations with Rapidly Decaying Periods
We observed the 1991 October outburst of EF Peg. Prominent superhumpswith a period of 0.08705(1)d were observed, qualifying EF Peg as being along-period SU UMa-type dwarf nova. The superhump period showed amonotonic decrease during the superoutburst, which makes a contrast tothe virtually zero period change observed during the 1997 superoutburstof the same object. Large-amplitude and highly coherent quasi-periodicoscillations (super-QPOs) were observed on October 18, when superhumpswere still growing in amplitude. Most strikingly, the QPOs showed arapid decrease in the period from 18min to 6.8min within the 3.2-hrobserving run. Such a rapid change in the period has not been observedin any class of QPOs in cataclysmic variables. We propose a hypothesisthat the rapid decrease of the QPO period reflects a rapid removal ofthe angular momentum from an orbiting blob in the accretion disk, viaviscosity in a turbulent disk. A brief comparison is given with the QPOsin X-ray binaries, some of which are known to show a similar rapiddecrease in the periods.
| 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
| An astrometric catalogue of stars in the region of M15
We present positions and proper motions with respect to the PPMcatalogue of 863 stars in a field of 8 deg x 6 deg centered on theglobular cluster M15. The catalogue is based on measurements of 136plates from the Carte du Ciel telescope of Bordeaux, the CERGA Schmidttelescope, and the double refractor of Bonn. The modal accuracy of theproper motions is +/- 0 arcsec 15/100 a.
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Pegazus |
| Rektaszcenzió: | 21h37m46.51s |
| Deklináció: | +15°03'28.2" |
| Vizuális fényesség: | 8.301 |
| Távolság: | 101.523 parszek |
| RA sajátmozgás: | 16.7 |
| Dec sajátmozgás: | -20.5 |
| B-T magnitude: | 8.692 |
| V-T magnitude: | 8.334 |
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