Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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 ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| A photometric study of wide visual double stars. III - Wide visual double stars with F-type primaries
Fifty-one wide visual double stars with F-type primaries have beenobserved in the uvby, H-beta system. MK class, color excess, absolutemagnitude, effective temperature and distance have been derived fromcalibrations of the above systems. From the distances derived here andthe astrometric data, taken from the literature, it appears that atleast 75 percent of them can be 'physical pairs'. Nevertheless, about 33percent of the double stars in this sample seem to have a realseparation of their components larger than 0.01 parsecs. That means thatthese stars are not gravitationally bound, but they have a commonorigin. For this season, the values of their astrophysical parametersare usually very close together.
| A photometric study of wide visual double stars. II - Common proper motion double stars
A total of 82 common proper motion wide visual double stars have beenobserved using the uvby, H-beta systems. MK class, color excess,absolute magnitude, effective temperature, and distance have beenderived from calibrations of the above systems. From the distancesderived here and the astrometric data, taken from the literature, it wasfound that the percentage of physical binaries among the common propermotion wide double stars is significantly higher than the samepercentage among the wide visual double stars with significant relativeproper motion, but there are a lot of optical pairs among them as well.
| Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. III - 790 late-type bright stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...59...15A&db_key=AST
| Close visual binaries. I - MK classifications
Each component of 170 close visual binaries has been classified with newprocedures for controlling contamination problems. These classificationsare presented and are shown to be on the MK system. Two sources of areascanner UBV photometry were compared in order to establish homogeneousphotometric as well as spectroscopic data. From a consideration ofsystematic errors in the V magnitude difference (Delta V) betweencomponents the photometry of Hurly and Warner (1983) is to be preferred.Absolute magnitudes for each binary are derived from Delta V via atested MK - M(v) map.
| Close visual binaries. II - Quantitative test of isochrones
Homogeneous and accurate color-magnitude data are available from Paper Ifor each component of 56 close visual binaries, 30 with evolvedcomponents. The 21 binaries with main-sequence primaries are comparedwith new Yale isochrones to determine the appropriate isochronecomposition: Y = 0.25, Z = 0.04. Explanations are given for eightbinaries found to be inconsistent with this isochrone. Some of theremaining binaries suggest a decrease by 0.5 in the mixing lengthparameter for the reddest main-sequence stars, and either a smallerdecrease or mass loss in the subgiant and giant phase of evolution. Ingeneral, the mean apparent age difference between binary components (0.0+ or - 0.1 Gyr) shows stellar evolution to be well modeled by the newYale isochrones.
| Area Scanner Observations of Close Visual Double Stars - Part Two - Results for 153 Southern Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.202..761H&db_key=AST
| Photographic observations of visual double stars
The results of photographic observations of 199 visual double stars,obtained at the Bosscha Observatory at Lembang, Indonesia, in the years1958-1975 (with one 1953 plate) are presented. The material comprises708 plates with an average of 37 images measured per plate. A shortdescription of the program is given (cf. van Albada-van Dien, 1958).
| Uvby-beta photometry of visual double stars - Absolute magnitudes of intrinsically bright stars
Individual absolute visual magnitudes M(v) are derived for intrinsicallybright stars and evolved stars. The results are collected for 106objects believed to be members of binary systems. uvby-beta photometrywas empirically calibrated in terms of M(v) for main sequence stars andphotoelectrically determined apparent magnitudes. The derived M(v)values are not significantly different from those stated in the Wilsoncatalogue (1976). Binary systems with main sequence primaries andsecondary components off the main sequence were also investigated.Several systems in which at least one component may be in the pre-mainsequence contraction stage are pointed out. A wide variety of commentsand derived data are given individually for 136 double stars, includingmetallicities, distance moduli, and masses.
| Erratum - Discordances Between SAO and HD Numbers for Bright Stars
Not Available
| UVBY photometry of wide visual double stars with B, A and F spectral type- I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
| Combined-light UBV Photometry of 103 Bright Southern Visual Doubles
Not Available
| H_alpha Photometry of Late-type Stars. II. F and G Type Dwarf Stars South of the Equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.131..467P&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Irmak |
| Sað Açýklýk: | 01h38m48.20s |
| Yükselim: | -53°26'20.0" |
| Görünürdeki Parlaklýk: | 6.84 |
| Uzaklýk: | 116.279 parsek |
| özdevim Sað Açýklýk: | -8 |
| özdevim Yükselim: | -43.8 |
| B-T magnitude: | 7.596 |
| V-T magnitude: | 7.154 |
Kataloglar ve belirtme:
|
