Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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
| 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
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
| The vertical structure of our galaxy. I - Methods of quantitative objective prism spectroscopy
The methods employed to determine the spectral types and log g and Fe/Hvalues for Galactic F-K stars in the vertical-structure investigation ofRose and Agustinho (1991) are described in detail. IIaO objective-prismplates obtained with the Curtis Schmidt telescope at CTIO using a 10-degprism and a 135-A FWHM interference filter centered at 408 nm aredigitized, and three spectral indices defined by Rose (1984) aremeasured and used to calculate the desired parameters. Results fromtests of the accuracy of this method are presented, and it is shown thatreliable separation of G dwarfs from G giants/subgiants is possible downto B = 13.
| Red horizontal-branch stars in the galactic disk
A quantitative, three-dimensional spectral classification systemdeveloped by Rose (1984), which uses 2.5-A resolution spectra in theblue, has been used to identify a class of red horizontal branch (RHB)stars in the Galactic disk that are similar to those in the 'metal rich'globular cluster M 71. The RHB are denoted as evolved stars by their SrII 4077 line, and are distinguished from post-main sequence starsevolving through the same region of the HR diagram on the basis of theunique appearance of their CN 3883 and 4216 A bands. The RHB starsconsitute at least 5 percent of the entire giant branch population ofthe disk.
| Observations of lithium dilution and rotational velocity decay in F and G giant stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJ...195..649A&db_key=AST
| Advanced evolution in globular clusters. II - The ultraviolet-bright stars in omega Centauri
The results of a spectrographic and photometric survey of stars whichoccupy the region above the horizontal branch and to the left of thegiant branch (the so-called UV-bright region) in the color-magnitudediagram of the globular cluster omega Centauri are presented. There isno large scatter in the apparent metal abundances of the cool stars ROA164 and 342 and the red giant ROA 159. Helium lines are present in thespectra of ROA 3596 and 5701. A mean mass of about 0.58 solar mass(internal s.e.) is obtained for the UV-bright stars, indicating thatthey have the same mass as the blue horizontal-branch stars. Thedistribution of the UV-bright stars in the theoretical H-R diagramindicates that these objects can occupy any position in the UV-brightregion. This implies that if they are to be explained by loops resultingfrom helium shell flashes and/or by final evolution from the asymptoticbranch or the giant branch, the loops must be long and occur at a rangein luminosities, and/or the final evolution from the giant branches mustoccur at a range of luminosities.
| MK classifications for F and G-type stars. I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..916H&db_key=AST
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Hercules |
| Ascensió Recta: | 17h20m36.23s |
| Declinació: | +15°09'33.9" |
| Magnitud Aparent: | 7.135 |
| Distancia: | 135.135 parsecs |
| Moviment propi RA: | 11.1 |
| Moviment propi Dec: | -33.1 |
| B-T magnitude: | 7.82 |
| V-T magnitude: | 7.192 |
Catàlegs i designacions:
|
