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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
| The period and amplitude variations of δ Scuti star HD 93044.
The δ Scuti variable star HD 93044 was observed with the 60cmtelescope at the Xinglong Station of the Beijing AstronomicalObservatory from 1992 to 1993. Period analyses were made for the 1992data set, the 1993 data set, and the combined 1992-1993 data set.Besides the known three frequencies: 11.90809, 16.798 and 22.074c/d, twonew frequencies of 2.086 and 10.489c/d were found. Some amplitudevariations of two pulsation components (11.90809, 22.074c/d) wereobvious. The new frequency of 2.086c/d might be the interaction modefrom which the resonances can occur and then lead to the nonlinearphenomena in the δ Scuti variable star.
| Period analysis of the Delta Scuti star HD93044
HD93044 was observed electrophotometricaly on April 21, May 1, 2 and 4,1991 at Xinglong Station of Beijing Astronomical Observatory. The datawas combined together with Li Zhiping's data and a period analysis wascompleted using a program which consists of a combination of Fouriertranforms of prewhitened data and the multifrequency least squares ofbrightness residuals (LSR). There pulsation frequencies (11.90809,16.79553, 22.44827 cycles per day) with visual amplitudes between 0.0056and 0.0203 mag were found. The solution fits the observations to +0.0071mag which is equal to the mean square deviation of observations. Thefirst frequency (11.90809 cycles per day) must be the right value of thefundamental frequency of HD93044.
| HD 93044: a New delta Scuti Variable?
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