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Ýlgili Makaleler
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).
| Chemical enrichment and star formation in the Milky Way disk. III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of theMilky Way disk, by using a sample composed by 424 late-type dwarfs. Weshow that the velocity dispersion of a stellar group correlates with theage of this group, according to a law proportional to t0.26,where t is the age of the stellar group. The temporal evolution of thevertex deviation is considered in detail. It is shown that the vertexdeviation does not seem to depend strongly on the age of the stellargroup. Previous studies in the literature seem to not have found it dueto the use of statistical ages for stellar groups, rather thanindividual ages. The possibility to use the orbital parameters of a starto derive information about its birthplace is investigated, and we showthat the mean galactocentric radius is likely to be the most reliablestellar birthplace indicator. However, this information cannot bepresently used to derive radial evolutionary constraints, due to anintrinsic bias present in all samples constructed from nearby stars. Anextensive discussion of the secular and stochastic heating mechanismscommonly invoked to explain the age-velocity dispersion relation ispresented. We suggest that the age-velocity dispersion relation couldreflect the gradual decrease in the turbulent velocity dispersion fromwhich disk stars form, a suggestion originally made by Tinsley &Larson (\cite{tinsley}, ApJ, 221, 554) and supported by several morerecent disk evolution calculations. A test to distinguish between thetwo types of models using high-redshift galaxies is proposed.Full Table 1 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/423/517
| 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
| Magnesium Isotopic Abundance Ratios in Cool Stars
From high-resolution spectra of 61 cool dwarfs and giants, Mg isotopicabundance ratios 24Mg:25Mg:26Mg arederived from spectral synthesis of the MgH A-X lines near 5140 Å.Our sample spans the range -2.5<=[Fe/H]<=0.1, including the firstmeasurements of Mg isotope ratios in stars with metallicities below[Fe/H]=-2.0. We confirm the decrease in 25Mg/24Mgand 26Mg/24Mg with decreasing [Fe/H], as predictedby recent models of Galactic chemical evolution in which the Mg isotopesare produced in massive stars. A subset of kinematically identifiedthin-disk stars have Mg isotope ratios in excellent agreement with thepredictions. Within the measurement uncertainties, these thin-disk starsshow no scatter about the predictions. Several of our stars are likelymembers of the thick disk, and their high Mg isotopic ratios may reflectthe nucleosynthetic history of the thick disk, which is distinct fromthe predictions for, and observations of, the thin disk. For thick-diskand halo stars we find a scatter in 25Mg/24Mg and26Mg/24Mg exceeding our measurement uncertaintiesand increasing with increasing metallicity. Our data suggest that anadditional source of 25Mg and 26Mg is required.Intermediate-mass asymptotic giant branch stars are likely candidates.
| A Search for Cool Subdwarfs: Stellar Parameters for 134 Candidates
The results of a search for cool subdwarfs are presented. Kinematic (U,V, and W) and stellar parameters (Teff, logg, [Fe/H], andξt) are derived for 134 candidate subdwarfs based onhigh-resolution spectra. The observed stars span 4200K
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Chromospherically young, kinematically old stars
We have investigated a group of stars known to have low chromosphericages, but high kinematical ages. Isochrone, chemical and lithium agesare estimated for them. The majority of stars in this group show lithiumabundances much smaller than expected for their chromospheric ages,which is interpreted as an indication of their old age. Radial velocitymeasurements in the literature also show that they are not closebinaries. The results suggest that they can be formed from thecoalescence of short-period binaries. Coalescence rates, calculatedtaking into account several observational data and a maximum theoreticaltime scale for contact, in a short-period pair, predict a number ofcoalesced stars similar to what we have found in the solarneighbourhood.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Metallicity effects on the chromospheric activity-age relation for late-type dwarfs
We show that there is a relationship between the age excess, defined asthe difference between the stellar isochrone and chromospheric ages, andthe metallicity as measured by the index [Fe/H] for late-type dwarfs.The chromospheric age tends to be lower than the isochrone age formetal-poor stars, and the opposite occurs for metal-rich objects. Wesuggest that this could be an effect of neglecting the metallicitydependence of the calibrated chromospheric emission-age relation. Wepropose a correction to account for this dependence. We also investigatethe metallicity distributions of these stars, and show that there aredistinct trends according to the chromospheric activity level. Inactivestars have a metallicity distribution which resembles the metallicitydistribution of solar neighbourhood stars, while active stars appear tobe concentrated in an activity strip on the logR'_HKx[Fe/H] diagram. Weprovide some explanations for these trends, and show that thechromospheric emission-age relation probably has different slopes on thetwo sides of the Vaughan-Preston gap.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| Chromospheric activity in evolved stars - The rotation-activity connection and the binary-single dichotomy
A tabulation of measured values of the Ca II H and K (S) index aretransformed to the original Mount Wilson definition of the index. Thetabulation includes main-sequence, evolved, single, and tidally coupled(RS CVn) binary stars. The (S) indices are analyzed against Wilson's(1976) I(HK) intensity estimates, showing that Wilson's estimates areonly a two-state indicator. Ca II H and K fluxes are computed andcalibrated with published values of rotation periods. It is found thatthe single and binary stars are consistent with a single relationshipbetween rotation and Ca II excess emission flux.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| A survey of chromospheric emission and rotation among solar-type stars in the solar neighborhood
A spectroscopic survey of Ca II and H and K emission among late-typedwarfs is analyzed in order to identify solar neighborhood stars with(B-V) greater than 0.50 and less than 1.00. The observations were usedto calculate RHK, the fraction of the bolometric luminosityof a star which appears as HK emission. The angular velocities of thestars relative to the sun (Omega/Omega solar radius) were calculatedbased on a calibration of RHK with the Rossby number. Therelationship between age and the rotational properties of the stars wasalso analyzed in detail. It is shown that for stars of a givenRHK, age RHK increases slightly with increasing(B-V). The activity-age relation (RHK varies as exp -1/2) wasfound to be independent of mass for the late-type dwarfs. Therotation-age relation was also independent of mass, and the rotationrate of the sun was found to be normal for a star of its mass and age.It is suggested that the age dependencies of chromospheric activity arealso unrelated to mass and angular momentum loss may be considered aself-regulating mechanism which is not related to the details of stellarstructure such as the convective zone depth.
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| Photometric parallaxes of nearby main-sequence stars with annual proper motion of 0.7 arcsec or more derived from Eggen's B, V and R, I data
The mean color-luminosity relations MV-(B-V),MV-(R-I), and MR-(R-I), for main-sequence stars inthe MV range +4 to +14, have been derived from the Eggen(1979, 1980) U, B, V, and/or R, I photometry for over 800 stars withannual proper motion of 0.7 arcsec or more. Only stars with goodtrigonometric parallax percent accuracies are employed. Photometricparallaxes greater than 0.04 arcsec are determined from these relationsfor the case of nearly 90 objects whose distances remain unknown, ofwhich the majority are red dwarfs.
| Spectral classification and photometry of high proper motion stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967AJ.....72.1334C&db_key=AST
| Etoiles doubles nouvelles decouvertes a l'Observatoire de Nice (2eme serie).
Not Available
| Stellar groups. III. The space motions of some main sequence dwarfs
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958MNRAS.118..560E&db_key=AST
| Photographic determination of the parallaxes of 55 stars with the Thaw refractor.
Not Available
| Magnitudes, colors and photometric parallaxes of proper motion stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..462E&db_key=AST
| A Catalogue of High-Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2..195R&db_key=AST
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