Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The Radial Velocity Experiment (rave): Second Data Release
We present the second data release of the Radial Velocity Experiment(RAVE), an ambitious spectroscopic survey to measure radial velocitiesand stellar atmosphere parameters (temperature, metallicity, surfacegravity, and rotational velocity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2 m UK Schmidt Telescope of theAnglo-Australian Observatory (AAO). The RAVE program started in 2003,obtaining medium resolution spectra (median R = 7500) in the Ca-tripletregion (8410-8795 Å) for southern hemisphere stars drawn from theTycho-2 and SuperCOSMOS catalogues, in the magnitude range 9 < I <12. Following the first data release, the current release doubles thesample of published radial velocities, now containing 51,829 radialvelocities for 49,327 individual stars observed on 141 nights between2003 April 11 and 2005 March 31. Comparison with external data setsshows that the new data collected since 2004 April 3 show a standarddeviation of 1.3 km s–1, about twice as good as for thefirst data release. For the first time, this data release containsvalues of stellar parameters from 22,407 spectra of 21,121 individualstars. They were derived by a penalized χ2 method usingan extensive grid of synthetic spectra calculated from the latestversion of Kurucz stellar atmosphere models. From comparison withexternal data sets, our conservative estimates of errors of the stellarparameters for a spectrum with an average signal-to-noise ratio (S/N) of~40 are 400 K in temperature, 0.5 dex in gravity, and 0.2 dex inmetallicity. We note however that, for all three stellar parameters, theinternal errors estimated from repeat RAVE observations of 855 stars areat least a factor 2 smaller. We demonstrate that the results show nosystematic offsets if compared to values derived from photometry orcomplementary spectroscopic analyses. The data release includes propermotions from Starnet2, Tycho-2, and UCAC2 catalogs and photometricmeasurements from Tycho-2 USNO-B, DENIS, and 2MASS. The data release canbe accessed via the RAVE Web site: http://www.rave-survey.org andthrough CDS.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| S0 galaxies in Fornax: data and kinematics
We have obtained long-slit spectroscopy for a sample of nine S0 galaxiesin the Fornax Cluster using the FORS2 spectrograph at the 8.2-m EuropeanSouthern Observatory (ESO) Very Large Telescope (VLT). From these data,we have extracted the kinematic parameters, comprising the meanvelocity, velocity dispersion and higher moment h3 andh4 coefficients, as a function of position along the majoraxes of these galaxies. Comparison with published kinematics indicatesthat earlier data are often limited by their lower signal-to-noise ratioand relatively poor spectral resolution. The greater depth and higherdispersion of the new data mean that we reach well beyond the bulges ofthese systems, probing their disc kinematics in some detail for thefirst time. Qualitative inspection of the results for individualgalaxies shows that they are not entirely simple systems, perhapsindicating a turbulent past. None the less, we are able to derivereliable circular velocities for most of these systems, which points theway towards a study of their Tully-Fisher relation. This study, alongwith an analysis of the stellar populations of these systems out tolarge galactocentric distances, will form the bases of future papersexploiting these new high-quality data, hopefully shedding new light onthe evolutionary history of these systems.
| Metallicity and absolute magnitude calibrations for UBV photometry
Calibrations are presented here for metallicity ([Fe/H]) in terms of theultraviolet excess, [δ(U - B) at B - V = 0.6, hereafterδ0.6], and also for the absolute visual magnitude(MV) and its difference with respect to the Hyades(ΔMHV) in terms of δ0.6 and(B - V), making use of high-resolution spectroscopic abundances from theliterature and Hipparcos parallaxes. The relation[Fe/H]-δ0.6 has been derived for dwarf plus turn-offstars, and also for dwarf, turn-off, plus subgiant stars classifiedusing the MV-(B - V)0 plane of Fig. 11, which iscalibrated with isochrones from Bergbusch & VandenBerg (and alsoVandenBerg & Clem). The [Fe/H]-δ0.6 relations inour equations (5) and (6) agree well with those of Carney, as can beseen from Fig. 5(a). Within the uncertainties, the zero-points,+0.13(+/-0.05) of equation (5) and +0.13(+/-0.04) of equation (6), arein good agreement with the photometric ones of Cameron and of Carney,and close to the spectroscopic ones of Cayrel et al. and of Boesgaard& Friel for the Hyades open cluster. Good quantitative agreementbetween our estimated [Fe/H] abundances with those from uvby-βphotometry and spectroscopic [Fe/H]spec values demonstratesthat our equation (6) can be used in deriving quality photometric metalabundances for field stars and clusters using UBV data from variousphotometric surveys.For dwarf and turn-off stars, a new hybrid MV calibration ispresented, based on Hipparcos parallaxes withσπ/π <= 0.1 and with a dispersion of +/-0.24in MV. This hybrid MV calibration containsδ0.6 and (B - V) terms, plus higher order cross-termsof these, and is valid for the ranges of +0.37 <= (B - V)0<= +0.88,- 0.10 <= δ0.6 <= +0.29 and 3.44<= MV <= 7.23. For dwarf and turn-off stars, therelation for ΔMHV is revised and updated interms of (B - V) and δ0.6, for the ranges of -0.10<= δ0.6 <= +0.29, and +0.49 <= (B -V)0 <= +0.89, again making use of Hipparcos parallaxeswith σπ/π <= 0.1. These parallaxes formetal-poor dwarf and turn-off stars in our sample reveal that thedifference of ΔMHV(B - V) relative to Hyadesat (B - V) = +0.70 should be 1.37mag, instead of the 1.58mag given byLaird et al. In general, Hipparcos parallaxes are larger thanground-based ones, causing a divergence of ourΔMHV(B - V,δ0.6) relation(the solid line in Fig. 15b), from the one of Laird et al. (the dashedline) for the range +0.10 <= δ0.6 <= +0.29 ourabsolute magnitudes are fainter, as has been confirmed for localsubdwarfs by Reid. Our final calibrations forΔMHV(B - V, δ0.6),equations (16) and (17), are third-order polynomials inδ0.6, pass through the origin, and provide photometricdistances in reasonable agreement with those obtained directly fromHipparcos parallaxes (Fig. 18).
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| 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.
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:/ /cdsweb.u-strasbg.fr/ cgi-bin/qcat?J/ A+A/394/927
| 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.
| 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
| Photometric Abundance Calibration of delta Scuti Stars Using HK Photometry
The hk index has been used as a metallicity indicator for RR Lyraevariable stars. It is now being applied to the shorter period deltaScuti variables. Employing spectroscopic abundances of stars withpublished hk values and photometric indices calculated from stellaratmosphere models, a three-dimensional interpolation is used todetermine [Fe/H] from intrinsic b-y, c_1, and hk values. The resulting[Fe/H], log g, and T_eff values for 10 delta Scuti stars are presented.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| Astrometric positions of stars with high proper motions in the Southern Hemisphere
Several stars with large proper motions, cited by W.J. Luyten, wereincluded in the preliminary programme for the HIPPARCOS mission. Whenperforming preparatory measurements of plates, difficulties wereencountered in identifying certain of these stars when relying only onpublished coordinates. We have taken advantage of this work whichrelates to the southern sky in order to determine the astrometricposition of the greatest possible number of these objects, even forthose which were not included in the programme. Catalogue is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Abundance of CN. Calcium and Heavy Elements in High Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..825E&db_key=AST
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| New beryllium observations in low-metallicity stars.
We present observations of the Be II 313.0nm resonance doublet in 14halo and old disk stars with metallicities ranging from [Fe/H]=-0.4 to=~-3.0 obtained with the CASPEC spectrograph of the ESO 3.6m telescopeat a FWHM=~8.6km/s resolution. Abundances are derived by means of thesynthetic spectra technique employing Kurucz (1993) atmospheric models,with enhanced α-elements and no overshooting. The derivedabundances together with those available in literature show that for-2.7<[Fe/H]<-0.8 Be correlates linearly with iron[Be]{prop.to}1.07(+/-0.08)[Fe/H], giving strength to previous results.However, a steeper correlation is still possible at metallicities lowerthan [Fe/H]<-1.4 with [Be]{prop.to} 1.6(+/-0.44)[Fe/H]. When iron isreplaced with oxygen, Be is found tracking closely oxygen up to solarvalues, without signs of breaking in correspondence of the onset of theGalactic disk. No evidence of intrinsic dispersion is found, ought tothe large errors involved in the Be abundance determinations, but forthree stars (HD 106516, HD 3795, HD 211998) a significant upper limit inthe Be abundance can be placed at =~1dex below the mean trend of theBe-Fe relation. For such stars non conventional mixing is required toexplain Be depletion. Be observations can be used to discriminatestrongly Li-depleted stars. These are the stars which show less Li thanthat expected by high energy cosmic rays production as deduced from Beobservations. The available Be observations imply that some of the starswhich contribute to the scatter in the Li-Fe diagram are Li-depletedstars. This result strongly supports the use of the upper envelope ofthe Li-Fe diagram to trace the Li galactic evolution, and argues for alow value for the primordial Li against models which predict substantialLi depletion in halo and old disk stars.
| The catalogue of nearby stars metallicities.
Not Available
| Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2771W&db_key=AST
| 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.
| Spectroscopic analyses of metal-poor stars. III. Magnesium abundances.
We present magnesium abundances and Mg/Fe ratios for 56 metal-poordwarfs and subgiants based on differential LTE model atmosphere analysesof spectra that have a typical S/N of 50-100 and a resolution of about20000-30000. The distribution of Mg/Fe abundance ratios with Feabundances is characterized by a steep increase of [Mg/Fe] near[Fe/H]=-0.6. At that iron abundance we recognize an abrupt change from asolar value for stars with [Fe/H]>=-0.6 to an upper limit of +0.4dexfor the metal-poor stars. Our data suggest that this step in the Mg/Feabundance ratio at [Fe/H]=-0.6 is the result of the onset of Galacticdisk formation, whereas [Mg/Fe]=+0.4 apparently is an upper limitarising from the constraints of nucleosynthesis in massive SN II eventsduring the first stellar generations, the yields of which we observe inthe most metal-poor halo stars.
| Spectroscopic analyses of metal-poor stars. II. The evolutionary stage of subdwarfs.
Models of post-main sequence stellar evolution of VandenBerg & Bell(???) have been applied to determine spectroscopic masses and distancesfor metal-poor stars. Careful consideration of the most important errorsources published in more recent papers such as VandenBerg (???) for thefirst time allow us to draw firm statistical conclusions. It is shownthat the evolutionary calculations qualitatively fit to the observedstellar parameters whereas quantitatively they predict too high ages formetal-poor stars. As an important result we confirm that evolutionarysequences need to be calibrated with respect to their metal abundance inorder to use their absolute predictions of temperature and luminosity.It turns out that this can be achieved by a simple shift of theevolutionary tracks and isochrones in effective temperature with values{DELTA}log T_eff_<~0.03 which accounts for possible changes of themixing-length and the O/Fe ratio with metallicity. The stellarluminosities and surface gravities obtained from evolutionary models aremuch more reliable than their effective temperatures. Therefore weconclude that the accuracy of the corresponding spectroscopic stellargravities is systematically affected by deviations from LTE, inparticular along the subgiant sequence where systematic errors less than{DELTA}log g =~0.3 must be ascribed to the non-LTE ionizationequilibrium of Fe II/Fe I. In our spectroscopic analyses the strongdependence between surface gravity and abundances determined from Fe Ilines restricts the accuracy of Fe abundances in subgiants to 0.1 dex atbest. The most remarkable result of our evolutionary and kinematicinvestigations of halo stars refers to the large fraction of slightlyevolved subgiants among the so-called subdwarfs. Since conventionalphotometric approaches often assume that the great majority ofmetal-poor stars are dwarfs this results in distances that aresystematically too low for their samples. Consequently, significantdifferences are found when comparing evolutionary and kinematicparameters obtained from either photometric or spectroscopic data. Wedemonstrate this by comparing the space velocities of the stars. Itappears that stars with particularly high space velocities derived fromspectroscopic distances show very often much lower velocities based ontheir main sequence parallaxes. We find that results refering to mainsequence parallaxes are doubtful and can be used only with greatestcare. An advantageous side-effect of the application of spectroscopicdata to evolutionary calculations is the possibility to identify binarysystems that are either standing out from the Toomre diagram with theirunusually high space velocities, or from a log g - log T_eff_ diagramwith apparently contradictory luminosities.
| 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
| Spectroscopic analyses of metal-poor stars. 1: Basic data and stellar parameters
Accurate stellar parameters have been obtained from the analyses of morethan thousand spectra of 115 metal-poor dwarfs and subgiants with visualmagnitudes brighter than V approximately equal to 12. The stellar samplewas selected mainly by high proper motion, with additional restrictionsfrom B-V colors and U-B excesses. The effective temperatures cover arange from 5000 to 6500 K while abundances are found between (M/H) =-0.1 and -0.3 dex. Based on homogeneous ODF blanketed model atmospheresin local thermodynamic equilibrium (LTE) and working differentially withrespect to the Sun we derive a consistent set of stellar parameters,effective temperature, surface gravity, metal abundance andmicroturbulence velocity. Individual profile synthesis is applied to anumber of spectral lines for each star, which has led as a rule toaccuracies in Teff of better than 100 K, in log g of betterthan 0.15, and in (Fe/H) of better than 0.1 dex. Because of theconsistent treatment with only one type of model atmosphere, this sampleprovides an oppurtunity to examine the individual parametersstatistically and investigate in detail their relation to the formationand evolution of the Galaxy. One aspect of this analysis is a generalshift to higher iron abundances for the most metal-poor stars. Alongwith the recently preferred meteoritic solar iron abundance andeffective temperatures from conistent Balmer line profile fits that tendto be 100-200 K hotter than found from photometric calibrations,discrepancies of up to 0.5 dex in (Fe/H) can be explained in comparisonwith other abundance analyses. The most important results refer to theevolutionary status of the bona fide subdwarf sample. Irrespective ofthe different effective temperatures found here, there exists a severeproblem when comparing post main sequence evolutionary models of coolstars with our observed parameters. Even more interesting is the fact,demonstrated by the results of a consistent analysis of the ironionization equilibrium, that roughly half of the subdwarfs aresubgiants, some of them having nearly reached the bottom of the giantbranch.
| Balmer lines in cool dwarf stars II. Effective temperatures and calibration of colour indices
Effective temperatures obtained from synthesis of the extended profilewings of the first four Balmer lines are presented for more than 100dwarfs and subgiants of different metal abundances and surface gravitiesin the temperature range from 5000 to 6500 K. Line formation is based onhomogeneous ODF blanketed model atmospheres in LTE. The resultingtemperatures of the more metal-rich stars differ systematically fromthose determined by reference to synthetic broad- or intermediate-bandcolours such as B-V , b-y , R-I or V-K . While the Balmer linetemperatures give room to only very small individual errors and resultin a convincingly small mean error for all four lines, the scatteragainst temperatures determined from broad-band colours is by faroutside the internal errors claimed in recent applications. This may beattributed to either (a) observational errors, (b) dependence on therelative mixture of metal abundances, (c) unknown line blocking in mostof the visible and near-infrared spectrum or (d) the inhomogeneity foundin the granular patterns of stellar surfaces. Our results suggest thatbroad-band colours are insufficient individual temperature indicators,reliable only in a statistical sense.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| Subdwarf studies. II - Abundances and kinematics from medium resolution spectra. III - The halo metallicity distribution
Stars previously identified as having UV excesses are observed at 1-Aresolution in the Ca II K-line region. Comparisons of these data withother samples and with Monte Carlo simulations involving a singlecomponent halo have yielded estimates of halo velocity dispersions androtation velocity, corrected for the kinematic biases in the sample. Itis suggested that the data are not consistent with a model in which thehalo formed from star formation in a dissipating, collapsing cloud; theyare, however, reconcilable with the formation of the halo stars bynumerous, independently evolving gas clouds. The metallicitydistribution of a sample of 372 kinematically selected halo stars isthen constructed, with a view to selection effects in the data. Goodagreement is noted between the globular cluster metallicity distributionand a stochastic model with a mean of 10 enrichments/fragment.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kemence |
| Rektaszcenzió: | 02h40m38.78s |
| Deklináció: | -30°08'07.5" |
| Vizuális fényesség: | 8.036 |
| Távolság: | 63.816 parszek |
| RA sajátmozgás: | 570 |
| Dec sajátmozgás: | 75.1 |
| B-T magnitude: | 8.693 |
| V-T magnitude: | 8.091 |
Katalógusok és elnevezések:
|
