Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| Lithium in population I subgiants
We present a lithium survey for a sample of 91 Pop. I stars. JHKLphotometry was also obtained for 61 stars in the sample. Besides Liabundances, [Fe/H] values were derived. Thanks to Hipparcos parallaxes,we could infer absolute V magnitudes for our sample stars and were ableto place them on the color-magnitude diagram, which allowed us toconstrain their evolutionary status. Masses and ages were derived formost of the stars by comparison with evolutionary tracks. The sample wasoriginally selected so to include class IV stars later thanspectral-type F0, but, based on the location on the color-magnitudediagram, we found a posteriori that a fraction of the stars (about 20%)are either main sequence stars or evolved giants. As it is the case fordwarfs and giants, a large spread in lithium abundance is present amongthe subgiants in our sample. As expected, the average lithium decreasesas the stars evolve along the subgiant branch; however, there is not aone-to-one relationship between the position on the color-magnitudediagram and lithium abundance, and the observed dispersion is onlypartially explainable as due to a dispersion in mass, metallicity, andage. In particular, a dispersion in lithium is seen among slightlyevolved subgiants with masses close to solar but in the sameevolutionary stage as the G2 IV star beta Hyi. The comparison of thebeta Hyi-like sample with a sample of non evolved solar-like starsindeed suggests that beta Hyi has most likely evolved from a mainsequence Li-rich star, rather than from a Li-poor star (like the Sun)that has dredged-up previously stored lithium. Our sample includesseveral stars that have completed the first-dredge up lithium dilution,but that have not yet evolved to the evolutionary point whereextra-mixing in the giant phase is thought to occur. A large number ofthem have Li abundances considerably below the theoretical predictionsof first dredge-up dilution. We confirm that this is due to the factthat the progenitors of these stars are most likely stars that havedepleted lithium while on the main sequence; the fraction of post-dredgeup Li rich/poor stars, in fact, is consistent with the observeddistribution of Li abundances among stars that have just left the mainsequence. The signature of the second mixing (or RGB extra-mixing)episode is evident in the log n(Li) vs. B-V and log n(Li) vs. M_boldistributions of the stars in the sample; it seems however that theextra-mixing occurs at luminosities lower than predicted by the modelsof Charbonnel (1994). Finally, a few evolved giants are found thatshould have passed the second mixing episode, but that do not show signsof it. At least half of them are spectroscopic binaries. Based onobservations carried out at the European Southern Observatory, La Silla,Chile
| Lithium and rotation on the subgiant branch. I. Observations and spectral analysis
We have obtained new high resolution spectroscopic observations of thelithium line at 6707.81 Angstroms and derived lithium abundances (A_Li )by spectral synthesis for a sample of about 120 F-, G- and K-typePopulation I subgiant stars. For each of these stars, high precisionrotational velocity obtained with the CORAVEL spectrometer is available.We present the behavior of the lithium abundance as a function ofeffective temperature, which shows a sort of discontinuity around 5600K, somewhat later than the well known rotational discontinuity. based onobservations collected at the Observatoire de Haute--Provence (France)and at the European Southern Observatory, La Silla (Chile).
| 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 large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| Large and kinematically unbiased samples of G- and K-type stars. IV - Evolved stars of the old disk population
Modified Stromgren and (R,I) photometry, along with DDO and Genevaphotometry, are presented for a complete sample of evolved old-disk Gand K giants in the Bright Star Catalogue. Stars with ages of between1.5 x 10 to the 9th and 10 to the 10th yr are found to have anear-normal distribution of heavy element abundances, centered on anFe/H abundance ratio of -0.1 dex. The old disk clusters NGC 3680 and IC4651 contain red-straggler young-disk giants that are probablycontemporaries of the blue stragglers in the clusters.
| Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
| 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
| Narrow-Band and Broad-Band Photometry of Red Stars. III. Southern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..199E&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: | Carina |
| Ascensió Recta: | 09h51m12.10s |
| Declinació: | -59°25'33.0" |
| Magnitud Aparent: | 5.79 |
| Distancia: | 228.833 parsecs |
| Moviment propi RA: | 30.5 |
| Moviment propi Dec: | -42.5 |
| B-T magnitude: | 7.547 |
| V-T magnitude: | 5.934 |
Catàlegs i designacions:
|
