Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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
| Mining the Metal-rich Stars for Planets
We examine the correlation between stellar metallicity and the presenceof short-period planets. It appears that approximately 1% of dwarf starsin the solar neighborhood harbor short-period planets characterized bynear-circular orbits and orbital periods P<20 days. However, amongthe most metal-rich stars (defined as having [Fe/H]>0.2 dex), itappears that the fraction increases to 10%. Using the Hipparcos databaseand the Hauck & Mermilliod compilation of Strömgren uvbyphotometry, we identify a sample of 206 metal-rich stars of spectraltype K, G and F which have an enhanced probability of harboringshort-period planets. Many of these stars would be excellent candidatesfor addition to radial velocity surveys. We have searched the Hipparcosepoch photometry for transiting planets within our 206 star catalog. Wefind that the quality of the Hipparcos data is not high enough to permitunambiguous transit detections. It is, however, possible to identifycandidate transit periods. We then discuss various ramifications of thestellar metallicity-planet connection. First, we show that there ispreliminary evidence for increasing metallicity with increasing stellarmass among known planet-bearing stars. This trend can be explained by ascenario in which planet-bearing stars accrete an average of 30M⊕ of rocky material after the gaseous protoplanetarydisk phase has ended. We present dynamical calculations which suggestthat a survey of metallicities of spectroscopic binary stars can be usedto understand the root cause of the stellar metallicity-planetconnection.
| 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
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Индус |
| Ректацензија: | 21h45m11.96s |
| Deклинација: | -50°26'47.7" |
| Apparent магнитуда: | 8.323 |
| Даљина: | 64.683 parsecs |
| Proper motion RA: | -43.7 |
| Proper motion Dec: | -78 |
| B-T magnitude: | 9.118 |
| V-T magnitude: | 8.389 |
Каталог и designations:
|
