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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
| Radial velocities, rotations, and duplicity of a sample of early F-type dwarfs
We present new radial and rotational velocities for 595 nearby early Fdwarfs, based on digital spectra cross-correlated with individuallyoptimised synthetic template spectra. The selection of optimumtemplates, the determination of rotational velocities, and theextraction of velocities from the blended spectra of double-linedspectroscopic binaries are discussed in some detail. We find 170spectroscopic binaries in the sample and determine orbits for 18double-lined and 2 single-lined binaries, including some spectroscopictriples. 73 stars are listed with too rapid rotation to yield usefulradial velocities (i.e. v sin i > 120 km~s^-1). We discuss the binaryfrequency in the sample, and the influence of unrecognised binaries onthe definition of clean metallicity groups of young F dwarfs and thedetermination of their kinematical properties. Tables 1, 5 and 6 areonly available, and Tables 2-4 also available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| Surface inhomogenetics on SZ PISCIUM
Ultraviolet and optical data are used to look at surface inhomogeneitieson the active close binary system SZ Piscium. Lower chromosphericemission lines such as Mg II h&k, and to a lesser extent the upperchromospheric/lower transition region lines of O I 1305A and C II 1335Sshow a pronounced decrease when the F star is eclipising the Ksub-giant. However, higher temperature lines such as the resonance lineof C IV 1550A do not show any change in flux. This suggest the presenceof a plage with a high contrast at lower temperatures with a Mg IIplage-to-K-star ratio of 5. Alternative explanations are explored.Monitoring of this system in the optical U-band and the ultravioletlines such as CIV 1550A, indicates frequent high energy1035-1036 flares.
| Blue straggler stars in the ultraviolet
The spectra of 27 blue straggler stars from galactic clusters and fromthe field, observed between 1150 and 3200 A, with the IUE are comparedwith data of normal stars of similar temperatures. Results show in allthe A type stars an absorption in the region 1200 to 2000 A similar tothat existing in Ap(Si) stars.
| The binary frequency of extreme subdwarfs revisited
Spectroscopic observations of 70 extreme subdwarfs, obtained over a 4-yrperiod with the 1.8-m telescope at Dominion Astrophysical Observatory,are presented in tables and analyzed statistically along with the datareported by Abt and Levy (AL; 1969) and Crampton and Hartwick (CH;1972). The data-reduction procedures and statistical techniques employedare explained, and significance limits are established by performingsimilar analyses for known binary stars. For a subsample of 46 subdwarfswith at least three observations spanning 100 d or more, abinary-frequency lower limit of 20-30 percent and a semiamplitude limitof about 14 km/s are determined, with similar frequencies for a set of12 subdwarfs with Fe/H less than -1.5 and for the samples of AL and CH.The reasons for the discrepancy between these findings and the lowfrequencies (0-15 percent) calculated by AL and CH are examined, and alist of binary candidates for observation is provided.
| Photometry among the Climatically Underprivileged
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| A puzzle for stellar astronomers.
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| HD 219150 - A star with a remarkable ultraviolet excess
HD 219150, an F0 V star with a one-quarter magnitude excess in (U-B) asshown by UBVRI and four-color-H beta observations, is discussed. Anattempt is made to explain this excess by examining metal deficiency inHD 219150 and by seeking an extremely hot subdwarf companion.Spectrograms at both classification and higher dispersions discountedthe first possibility, while far ultraviolet data and radial-velocitymeasurements eliminated the second. Computation of the fluxes expectedfrom free-bound Balmer emission and free-free emission from an opticallythin gas also proved unsuccessful in explaining the ultraviolet data.Also considered was variability on a long time scale, but the star wasfound constant in light, including U, to better than 0.01 m over fourmonths of observation.
| Spectral types of stars with unusual photometric indices
The Kitt Peak 2.1-m Cassegrain spectrograph was used to obtain spectraof 92 A5-G0 stars measured by Olsen in the Stromgren four-color systemand predicted to be abnormal in the sense of excessive reddening, highluminosity, or abnormal composition. Of the five stars predicted to bereddened B or A stars, four were indeed such while for the fifth Olsenobserved the blended components. Of twelve stars predicted to besupergiants, one is a supergiant, four are giants, two are subgiants,three are Ap stars, and two are Am stars. Thus photometrically predictedsupergiants are actually stars above main sequence in two out of threecases but mostly much less luminous than expected. Of ten predictedweak-lined stars, only two were found to be really so. Am stars werewell predicted, though detection is contaminated with Ap and luminousstars. It is concluded that four-color photometry is useful in selectinginteresting stars, but is often unable to tell the specific type ofabnormality present.
| New Variable HD 219018, the Comparison Star of SZ Psc
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| Estimation of spectral classifications for bright southern stars with interesting Stromgren indices
This paper investigates the degree of success with which uvby photometrycan be applied to predict spectral classifications for 947 A, F, and Gstars brighter than an apparent magnitude of 8.3 and with four-colorindices indicating some kind of interesting, unusual, or peculiarspectrum. One or several possible spectral classifications are estimatedfor each star from photometry alone, double stars are distinguished, andthe estimates are compared with published classifications. The resultsshow that the framework provided by uvby photometry can be extended toinclude most G and K stars, reddened stars, peculiar stars, and certaintypes of double star.
| Mesures d'étoiles doubles effectuées au réfracteur de 38 cm de l'Observatoires de Nice
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| Takýmyýldýz: | Baliklar |
| Sað Açýklýk: | 23h13m41.04s |
| Yükselim: | +02°12'12.9" |
| Görünürdeki Parlaklýk: | 7.186 |
| Uzaklýk: | 69.013 parsek |
| özdevim Sað Açýklýk: | 11.4 |
| özdevim Yükselim: | 39 |
| B-T magnitude: | 7.63 |
| V-T magnitude: | 7.223 |
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