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A catalog of rotational and radial velocities for evolved stars. IV. Metal-poor stars^
Aims.The present paper describes the first results of an observationalprogram intended to refine and extend the existing v sin i measurementsof metal-poor stars, with an emphasis on field evolved stars.Methods: .The survey was carried out with the FEROS and CORALIEspectrometers. For the v sin i measurements, obtained from spectralsynthesis, we estimate an uncertainty of about 2.0 km s-1. Results: .Precise rotational velocities v sin i are presented for alarge sample of 100 metal-poor stars, most of them evolving off themain-sequence. For the large majority of the stars composing the presentsample, rotational velocities have been measured for the first time.
| 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.
| 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).
| Sulphur abundance in Galactic stars
We investigate sulphur abundance in 74 Galactic stars by using highresolution spectra obtained at ESO VLT and NTT telescopes. For the firsttime the abundances are derived, where possible, from three opticalmultiplets: Mult. 1, 6, and 8. By combining our own measurements withdata in the literature we assemble a sample of 253 stars in themetallicity range -3.2 [Fe/H] +0.5. Two important features,which could hardly be detected in smaller samples, are obvious from thislarge sample: 1) a sizeable scatter in [S/Fe] ratios around [Fe/H]-1; 2) at low metallicities we observe stars with [S/Fe] 0.4, aswell as stars with higher [S/Fe] ratios. The latter do not seem to bekinematically different from the former ones. Whether the latter findingstems from a distinct population of metal-poor stars or simply from anincreased scatter in sulphur abundances remains an open question.
| Abundance trends in kinematical groups of the Milky Way's disk
We have compiled a large catalogue of metallicities and abundance ratiosfrom the literature in order to investigate abundance trends of severalalpha and iron peak elements in the thin disk and the thick disk of theGalaxy. The catalogue includes 743 stars with abundances of Fe, O, Mg,Ca, Ti, Si, Na, Ni and Al in the metallicity range -1.30 < [Fe/H]< +0.50. We have checked that systematic differences betweenabundances measured in the different studies were lower than randomerrors before combining them. Accurate distances and proper motions fromHipparcos and radial velocities from several sources have been retreivedfor 639 stars and their velocities (U, V, W) and galactic orbits havebeen computed. Ages of 322 stars have been estimated with a Bayesianmethod of isochrone fitting. Two samples kinematically representative ofthe thin and thick disks have been selected, taking into account theHercules stream which is intermediate in kinematics, but with a probabledynamical origin. Our results show that the two disks are chemicallywell separated, they overlap greatly in metallicity and both showparallel decreasing alpha elements with increasing metallicity, in theinterval -0.80 < [Fe/H] < -0.30. The Mg enhancement with respectto Fe of the thick disk is measured to be 0.14 dex. An even largerenhancement is observed for Al. The thick disk is clearly older than thethin disk with tentative evidence of an AMR over 2-3 Gyr and a hiatus instar formation before the formation of the thin disk. We do not observea vertical gradient in the metallicity of the thick disk. The Herculesstream has properties similar to that of the thin disk, with a widerrange of metallicity. Metal-rich stars assigned to the thick disk andsuper-metal-rich stars assigned to the thin disk appear as outliers inall their properties.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Nearby stars of the Galactic disk and halo. III.
High-resolution spectroscopic observations of about 150 nearby stars orstar systems are presented and discussed. The study of these and another100 objects of the previous papers of this series implies that theGalaxy became reality 13 or 14 Gyr ago with the implementation of amassive, rotationally-supported population of thick-disk stars. The veryhigh star formation rate in that phase gave rise to a rapid metalenrichment and an expulsion of gas in supernovae-driven Galactic winds,but was followed by a star formation gap for no less than three billionyears at the Sun's galactocentric distance. In a second phase, then, thethin disk - our ``familiar Milky Way'' - came on stage. Nowadays ittraces the bright side of the Galaxy, but it is also embedded in a hugecoffin of dead thick-disk stars that account for a large amount ofbaryonic dark matter. As opposed to this, cold-dark-matter-dominatedcosmologies that suggest a more gradual hierarchical buildup throughmergers of minor structures, though popular, are a poor description forthe Milky Way Galaxy - and by inference many other spirals as well - if,as the sample implies, the fossil records of its long-lived stars do notstick to this paradigm. Apart from this general picture that emergeswith reference to the entire sample stars, a good deal of the presentwork is however also concerned with detailed discussions of manyindividual objects. Among the most interesting we mention the bluestraggler or merger candidates HD 165401 and HD 137763/HD 137778, thelikely accretion of a giant planet or brown dwarf on 59 Vir in itsrecent history, and HD 63433 that proves to be a young solar analog at\tau200 Myr. Likewise, the secondary to HR 4867, formerly suspectednon-single from the Hipparcos astrometry, is directly detectable in thehigh-resolution spectroscopic tracings, whereas the visual binary \chiCet is instead at least triple, and presumably even quadruple. Withrespect to the nearby young stars a complete account of the Ursa MajorAssociation is presented, and we provide as well plain evidence foranother, the ``Hercules-Lyra Association'', the likely existence ofwhich was only realized in recent years. On account of its rotation,chemistry, and age we do confirm that the Sun is very typical among itsG-type neighbors; as to its kinematics, it appears however not unlikelythat the Sun's known low peculiar space velocity could indeed be thecause for the weak paleontological record of mass extinctions and majorimpact events on our parent planet during the most recent Galactic planepassage of the solar system. Although the significance of thiscorrelation certainly remains a matter of debate for years to come, wepoint in this context to the principal importance of the thick disk fora complete census with respect to the local surface and volumedensities. Other important effects that can be ascribed to this darkstellar population comprise (i) the observed plateau in the shape of theluminosity function of the local FGK stars, (ii) a small thoughsystematic effect on the basic solar motion, (iii) a reassessment of theterm ``asymmetrical drift velocity'' for the remainder (i.e. the thindisk) of the stellar objects, (iv) its ability to account for the bulkof the recently discovered high-velocity blue white dwarfs, (v) itsmajor contribution to the Sun's 220 km s-1 rotationalvelocity around the Galactic center, and (vi) the significant flatteningthat it imposes on the Milky Way's rotation curve. Finally we note ahigh multiplicity fraction in the small but volume-complete local sampleof stars of this ancient population. This in turn is highly suggestivefor a star formation scenario wherein the few existing single stellarobjects might only arise from either late mergers or the dynamicalejection of former triple or higher level star systems.
| Stellar Chemical Signatures and Hierarchical Galaxy Formation
To compare the chemistries of stars in the Milky Way dwarf spheroidal(dSph) satellite galaxies with stars in the Galaxy, we have compiled alarge sample of Galactic stellar abundances from the literature. Whenkinematic information is available, we have assigned the stars tostandard Galactic components through Bayesian classification based onGaussian velocity ellipsoids. As found in previous studies, the[α/Fe] ratios of most stars in the dSph galaxies are generallylower than similar metallicity Galactic stars in this extended sample.Our kinematically selected stars confirm this for the Galactic halo,thin-disk, and thick-disk components. There is marginal overlap in thelow [α/Fe] ratios between dSph stars and Galactic halo stars onextreme retrograde orbits (V<-420 km s-1), but this is notsupported by other element ratios. Other element ratios compared in thispaper include r- and s-process abundances, where we find a significantoffset in the [Y/Fe] ratios, which results in a large overabundance in[Ba/Y] in most dSph stars compared with Galactic stars. Thus, thechemical signatures of most of the dSph stars are distinct from thestars in each of the kinematic components of the Galaxy. This resultrules out continuous merging of low-mass galaxies similar to these dSphsatellites during the formation of the Galaxy. However, we do not ruleout very early merging of low-mass dwarf galaxies, since up to one-halfof the most metal-poor stars ([Fe/H]<=-1.8) have chemistries that arein fair agreement with Galactic halo stars. We also do not rule outmerging with higher mass galaxies, although we note that the LMC and theremnants of the Sgr dwarf galaxy are also chemically distinct from themajority of the Galactic halo stars. Formation of the Galaxy's thickdisk by heating of an old thin disk during a merger is also not ruledout; however, the Galaxy's thick disk itself cannot be comprised of theremnants from a low-mass (dSph) dwarf galaxy, nor of a high-mass dwarfgalaxy like the LMC or Sgr, because of differences in chemistry.The new and independent environments offered by the dSph galaxies alsoallow us to examine fundamental assumptions related to thenucleosynthesis of the elements. The metal-poor stars ([Fe/H]<=-1.8)in the dSph galaxies appear to have lower [Ca/Fe] and [Ti/Fe] than[Mg/Fe] ratios, unlike similar metallicity stars in the Galaxy.Predictions from the α-process (α-rich freeze-out) would beconsistent with this result if there have been a lack of hypernovae indSph galaxies. The α-process could also be responsible for thevery low Y abundances in the metal-poor stars in dSph's; since [La/Eu](and possibly [Ba/Eu]) are consistent with pure r-process results, thelow [Y/Eu] suggests a separate r-process site for this light(first-peak) r-process element. We also discuss SNe II rates and yieldsas other alternatives, however. In stars with higher metallicities([Fe/H]>=-1.8), contributions from the s-process are expected; [(Y,La, and Ba)/Eu] all rise as expected, and yet [Ba/Y] is still muchhigher in the dSph stars than similar metallicity Galactic stars. Thisresult is consistent with s-process contributions from lower metallicityAGB stars in dSph galaxies, and is in good agreement with the slowerchemical evolution expected in the low-mass dSph galaxies relative tothe Galaxy, such that the build-up of metals occurs over much longertimescales. Future investigations of nucleosynthetic constraints (aswell as galaxy formation and evolution) will require an examination ofmany stars within individual dwarf galaxies.Finally, the Na-Ni trend reported in 1997 by Nissen & Schuster isconfirmed in Galactic halo stars, but we discuss this in terms of thegeneral nucleosynthesis of neutron-rich elements. We do not confirm thatthe Na-Ni trend is related to the accretion of dSph galaxies in theGalactic halo.
| Heavy elements and chemical enrichment in globular clusters
High resolution (R 40 000) and high S/N spectra have been acquiredwith UVES on the VLT-Kueyen (Paranal Observatory, ESO Chile) for severalmain sequence turnoff stars (V 17 mag) and subgiants at the baseof the Red Giant Branch (V 16 mag) in three globular clusters (NGC6397, NGC 6752 and 47 Tuc/NGC 104) at different metallicities(respectively [Fe/H] ≃ -2.0; -1.5; -0.7). Spectra for a sample of25 field halo subdwarves have also been taken with equal resolution, buthigher S/N. These data have been used to determine the abundances ofseveral neutron-capture elements in these three clusters: strontium,yttrium, barium and europium. This is the first abundance determinationof these heavy elements for such unevolved stars in these three globularclusters. These values, together with the [Ba/Eu] and [Sr/Ba] abundanceratios, have been used to test the self-enrichment scenario. Acomparison is done with field halo stars and other well known Galacticglobular clusters in which heavy elements have already been measured inthe past, at least in bright giants (V 11-12 mag). Our resultsshow clearly that globular clusters have been uniformly enriched by r-and s-process syntheses, and that most of them seem to follow exactlythe same abundance patterns as field halo stars, which discards the``classical'' self-enrichment scenario for the origin of metallicitiesand heavy elements in globular clusters.Based on data collected at the European Southern Observatory with theVLT-UT2, Paranal, Chile (ESO-LP 165.L-0263).
| 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
| On the correlation of elemental abundances with kinematics among galactic disk stars
We have performed the detailed analysis of 174 high-resolution spectraof FGK dwarfs obtained with the ELODIE echelle spectrograph at theObservatoire de Haute-Provence. Abundances of Fe, Si and Ni have beendetermined from equivalent widths under LTE approximation, whereasabundances of Mg have been determined under NLTE approximation usingequivalent widths of 4 lines and profiles of 5 lines. Spatial velocitieswith an accuracy better than 1 km s-1, as well as orbits,have been computed for all stars. They have been used to define 2subsamples kinematically representative of the thin disk and the thickdisk in order to highlight their respective properties. A transitionoccurs at [Fe/H] =-0.3. Stars more metal-rich than this value have aflat distribution with Zmax;<1 kpc and σW<20 km s-1, and a narrow distribution of [α/Fe].There exist stars in this metallicity regime which cannot belong to thethin disk because of their excentric orbits, neither to the thick diskbecause of their low scale height. Several thin disk stars areidentified down to [Fe/H] =-0.80. Their Mg enrichment is lower thanthick disk stars with the same metallicity. We confirm from a largersample the results of Feltzing et al. (\cite{felt03}) and Bensby et al.(\cite{ben03}) showing a decrease of [α/Fe] with [Fe/H] in thethick disk interpreted as the signature of the SNIa which haveprogressively enriched the ISM with iron. However our data suggest thatthe star formation in the thick disk stopped when the enrichment was[Fe/H] =-0.30, [Mg/Fe] =+0.20, [Si/Fe] =+0.17. A vertical gradient in[α/Fe] may exist in the thick disk but should be confirmed with alarger sample. Finally we have identified 2 new candidates of the HR1614moving group.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute Provence (France).Tables 3 and 8 are 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/418/551
| Sodium Abundances in Stellar Atmospheres with Differing Metallicities
The non-LTE sodium abundances of 100 stars with metallicities-3<[Fe/H]<0.3 are determined using high-dispersion spectra withhigh signal-to-noise ratios. The sodium abundances [Na/Fe] obtained areclose to the solar abundance and display a smaller scatter than valuespublished previously. Giants (logg<3.8) with [Fe/H]<-1 do notdisplay overabundances of sodium, and their sodium abundances do notshow an anticorrelation with the oxygen abundance, in contrast toglobular-cluster giants. They likewise do not show sodium-abundancevariations with motion along the giant branch. No appreciable decreasein the sodium abundance was detected for dwarfs (logg>3.8) withmetallicities -2<[Fe/H]<-1. The observed relation between [Na/Fe]and [Fe/H] is in satisfactory agreement with the theoreticalcomputations of Samland, which take into account the metallicitydependence of the sodium yield and a number of other factors affectingthe distribution of elements in the Galaxy during the course of itsevolution.
| 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.
| Abundances for metal-poor stars with accurate parallaxes. I. Basic data
We present element-to-element abundance ratios measured from highdispersion spectra for 150 field subdwarfs and early subgiants withaccurate Hipparcos parallaxes (errors <20%). For 50 stars new spectrawere obtained with the UVES on Kueyen (VLT UT2), the McDonald 2.7 mtelescope, and SARG at TNG. Additionally, literature equivalent widthswere taken from the works by Nissen & Schuster, Fulbright, andProchaska et al. to complement our data. The whole sample includes boththick disk and halo stars (and a few thin disk stars); most stars havemetallicities in the range -2<[Fe/H]<-0.6. We found our data, thatof Nissen & Schuster, and that of Prochaska to be of comparablequality; results from Fulbright scatter a bit more, but they are stillof very good quality and are extremely useful due to the large size ofhis sample. The results of the present analysis will be used inforthcoming papers to discuss the chemical properties of thedissipational collapse and accretion components of our Galaxy.Based in part on data collected at the European Southern Observatory,Chile, at the MacDonald Observatory, Texas, USA, and at the TelescopioNazionale Galileo, Canary Island, INAF,Italy-Spain.}\fnmsep\thanks{Table 1 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia\resizebox{8.8cm}{2.2mm}htpp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/187}
| 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
| 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.
| Abundances and Kinematics of Field Stars. II. Kinematics and Abundance Relationships
As an investigation of the origin of ``α-poor'' halo stars, weanalyze kinematic and abundance data for 73 intermediate-metallicitystars (-1>[Fe/H]>=-2) selected from Paper I of this series. We findevidence for a connection between the kinematics and the enhancement ofcertain element-to-iron ([X/Fe]) ratios in these stars. Statisticallysignificant correlations were found between [X/Fe] and galacticrest-frame velocities (vRF) for Na, Mg, Al, Si, Ca, and Ni,with marginally significant correlations existing for Ti and Y as well.We also find that the [X/Fe] ratios for these elements all correlatewith a similar level of significance with [Na/Fe]. Finally, we comparethe abundances of these halo stars against those of stars in nearbydwarf spheroidal (dSph) galaxies. We find significant differencesbetween the abundance ratios in the dSph stars and halo stars of similarmetallicity. From this result, it is unlikely that the halo stars in thesolar neighborhood, including even the ``α-poor'' stars, were oncemembers of disrupted dSph galaxies similar to those studied to date.
| Abundances of Cu and Zn in metal-poor stars: Clues for Galaxy evolution
We present new observations of copper and zinc abundances in 90metal-poor stars, belonging to the metallicity range -3<[Fe/H]<-0.5. The present study is based on high resolutionspectroscopic measurements collected at the Haute Provence Observatoire(R= 42 000, S/N>100). The trend of Cu and Zn abundances as a functionof the metallicity [Fe/H] is discussed and compared to that of otherheavy elements beyond iron. We also estimate spatial velocities andgalactic orbital parameters for our target stars in order to disentanglethe population of disk stars from that of halo stars using kinematiccriteria. In the absence of a firm a priori knowledge of thenucleosynthesis mechanisms controlling Cu and Zn production, and of therelative stellar sites, we derive constraints on these last from thetrend of the observed ratios [Cu/Fe] and [Zn/Fe] throughout the historyof the Galaxy, as well as from a few well established properties ofbasic nucleosynthesis processes in stars. We thus confirm that theproduction of Cu and Zn requires a number of different sources (neutroncaptures in massive stars, s-processing in low and intermediate massstars, explosive nucleosynthesis in various supernova types). We alsoattempt a ranking of the relative roles played by different productionmechanisms, and verify these hints through a simple estimate of thegalactic enrichment in Cu and Zn. In agreement with suggestionspresented earlier, we find evidence that type Ia Supernovae must play arelevant role, especially for the production of Cu. Based on the spectracollected with the 1.93-m telescope of Haute Provence Observatory.
| Analysis of neutron capture elements in metal-poor stars
We derived model atmosphere parameters (Teff, log g, [Fe/H],Vt) for 90 metal-deficient stars (-0.5<[Fe/H]<-3),using echelle spectra from the ELODIE library (Soubiran et al.\cite{soubet98}). These parameters were analyzed and compared withcurrent determinations by other authors. The study of the followingelements was carried out: Mg, Si, Ca, Sr, Y, Ba, La, Ce, Nd, and Eu. Therelative contributions of s- and r-processes were evaluated andinterpreted through theoretical computations of the chemical evolutionof the Galaxy. The chemical evolution models (Pagel &Tautvaišienė \cite{pagta95}; Timmes et al. \cite{timet95})depict quite well the behaviour of [Si/Fe], [Ca/Fe] with [Fe/H]. Thetrend of [Mg/Fe] compares more favourably with the computations of Pagel& Tautvaišienė (\cite{pagta95}) than those of Timmes etal. (\cite{timet95}). The runs of n-capture elements vs. metallicity aredescribed well both by the model of Pagel & Tautvaišienė(\cite{pagta95}, \cite{pagta97}) and by the model of Travaglio et al.(\cite{travet99}) at [Fe/H]>-1.5, when the matter of the Galaxy issufficiently homogeneous. The analysis of n-capture element abundancesconfirms the jump in [Ba/Fe] at [Fe/H]=-2.5. Some stars from our sampleat [Fe/H]<-2.0 show a large scatter of Sr, Ba, Y, Ce. This scatter isnot caused by the errors in the measurements, and may reflect theinhomogeneous nature of the prestellar medium at early stages ofgalactic evolution. The matching of [Ba/Fe], [Eu/Fe] vs. [Fe/H] with theinhomogeneous model by Travaglio et al. (\cite{travet01a}) suggests thatat [Fe/H]<-2.5, the essential contribution to the n-rich elementabundances derives from the r-process. The main sources of theseprocesses may be low mass SN II. The larger dispersion of s-processelement abundances with respect to alpha -rich elements may arise bothfrom the birth of metal-poor stars in globular clusters with followingdifferent evolutionary paths and (or) from differences in s-elementenrichment in Galaxy populations. Based on spectra collected at theObservatoire de Haute-Provence (OHP), France
| On the stellar content of the open clusters Melotte 105, Hogg 15, Pismis 21 and Ruprecht 140
CCD observations in the B, V and I passbands have been used to generatecolour-magnitude diagrams reaching down to V ~ 19 mag for two slightlycharacterized (Melotte 105 and Hogg 15) and two almost unstudied (Pismis21 and Ruprecht 140) open clusters. The sample consists of about 1300stars observed in fields of about 4arcmin x4arcmin . Our analysis showsthat neither Pismis 21 nor Ruprecht 140 are genuine open clusters sinceno clear main sequences or other meaningful features can be seen intheir colour-magnitude diagrams. Melotte 105 and Hogg 15 are openclusters affected by E(B-V) = 0.42 +/- 0.03 and 0.95 +/- 0.05,respectively. Their distances to the Sun have been estimated as 2.2 +/-0.3 and 2.6 +/- 0.08 kpc, respectively, while the corresponding agesestimated from empirical isochrones fitted to the Main Sequence clustermembers are ~ 350 Myr and 300 Myr, respectively. The present data arenot consistent with the membership of the WN6 star HDE 311884 to Hogg15. Tables 2 to 5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.793.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/931
| The O-Na and Mg-Al anticorrelations in turn-off and early subgiants in globular clusters
High dispersion spectra (R>~ 40 000) for a quite large number ofstars at the main sequence turn-off and at the base of the giant branchin NGC 6397 and NGC 6752 were obtained with the UVES on Kueyen (VLTUT2). The [Fe/H] values we found are -2.03+/- 0.02+/- 0.04\ and -1.42+/-0.02+/- 0.04\ for NGC 6397 and NGC 6752 respectively, where the firsterror bars refer to internal and the second ones to systematic errors(within the abundance scale defined by our analysis of 25 subdwarfs withgood Hipparcos parallaxes). In both clusters the [Fe/H]'s obtained forTO-stars agree perfectly (within a few percent) with that obtained forstars at the base of the RGB. The [O/Fe]=0.21+/- 0.05 value we obtainfor NGC 6397 is quite low, but it agrees with previous results obtainedfor giants in this cluster. Moreover, the star-to-star scatter in both Oand Fe is very small, indicating that this small mass cluster ischemically very homogenous. On the other hand, our results show clearlyand for the first time that the O-Na anticorrelation (up to now seenonly for stars on the red giant branches of globular clusters) ispresent among unevolved stars in the globular cluster NGC 6752, a moremassive cluster than NGC 6397. A similar anticorrelation is present alsofor Mg and Al, and C and N. It is very difficult to explain the observedNa-O, and Mg-Al anticorrelation in NGC 6752 stars by a deep mixingscenario; we think it requires some non internal mechanism. Based ondata collected at the European Southern Observatory, Chile.
| Distances, Ages, and Epoch of Formation of Globular Clusters
We review the results on distances and absolute ages of Galacticglobular clusters (GCs) obtained after the release of the Hipparcoscatalog. Several methods aimed at the definition of the Population IIlocal distance scale are discussed, and their results compared,exploiting new results for RR Lyraes in the Large Magellanic Cloud(LMC). We find that the so-called short distance and long distancescales may be reconciled whether or not a consistent reddening scale isadopted for Cepheids and RR Lyrae variables in the LMC. Emphasis isgiven in the paper to the discussion of distances and ages of GCsderived using Hipparcos parallaxes of local subdwarfs. We find that theselection criteria adopted to choose the local subdwarfs, as well as thesize of the corrections applied to existing systematic biases, are themain culprit for the differences found among the various independentstudies that first used Hipparcos parallaxes and the subdwarf fittingtechnique. We also caution that the absolute age of M92 (usuallyconsidered one of the oldest clusters) still remains uncertain due tothe lack of subdwarfs of comparable metallicity with accurateparallaxes. Distances and ages for the nine clusters discussed in aprevious paper by Gratton et al. are rederived using an enlarged sampleof local subdwarfs, which includes about 90% of the metal-poor dwarfswith accurate parallaxes (Δπ/π<=0.12) in the wholeHipparcos catalog. On average, our revised distance moduli are decreasedby 0.04 mag with respect to Gratton et al. The corresponding age of theGCs is t=11.5+/-2.6 Gyr, where the error bars refer to the 95%confidence range. The relation between the zero-age horizontal branch(ZAHB) absolute magnitude and metallicity for the nine program clustersturns out to beMV(ZAHB)=(0.18+/-0.09)([Fe/H]+1.5)+(0.53+/-0.12) Thanks toHipparcos the major contribution to the total error budget associatedwith the subdwarf fitting technique has been moved from parallaxes tophotometric calibrations, reddening, and metallicity scale. This totaluncertainty still amounts to about +/-0.12 mag. We then compare thecorresponding (true) LMC distance modulusμLMC=18.64+/-0.12 mag with other existing determinations.We conclude that at present the best estimate for the distance of theLMC is μLMC=18.54+/-0.03+/-0.06, suggesting that distancesfrom the subdwarf fitting method are ~1 σ too long. Consequently,our best estimate for the age of the GCs is revised to Age=12.9+/-2.9Gyr (95% confidence range). The best relation between ZAHB absolutemagnitude and metallicity isMV(ZAHB)=(0.18+/-0.09)([Fe/H]+1.5)+(0.63+/-0.07). Finally, wecompare the ages of the GCs with the cosmic star formation rate recentlydetermined by studies of the Hubble Deep Field (HDF), exploiting thedeterminations of ΩM=0.3 andΩΛ=0.7 provided by Type Ia supernovae surveys.We find that the epoch of formation of the GCs (at z~3) matches well themaximum of the star formation rate for elliptical galaxies in the HDF asdetermined by Franceschini et al. Based on data from the Hipparcosastrometry satellite.
| Models for Old, Metal-poor Stars with Enhanced α-Element Abundances. I. Evolutionary Tracks and ZAHB Loci; Observational Constraints
Stellar evolutionary tracks have been computed for 17 [Fe/H] values from-2.31 to -0.30 assuming, in each case, [α/Fe]=0.0, 0.3, and 0.6.The helium abundance was assumed to vary from Y=0.2352 at [Fe/H]=-2.31to Y=0.2550 at [Fe/H]=-0.30 and held constant for the different choicesof [α/Fe] at a fixed iron content. Masses in the range0.5<=Msolar<=1.0, in 0.1 Msolarsteps, were generally considered, though sequences for higher massvalues were computed, as necessary, to ensure that isochrones as``young'' as 8 Gyr could be generated for each grid. All of the stellarmodels are based on an equation of state that treats nonideal effects,the latest nuclear reaction and neutrino cooling rates, and opacitiesthat were computed specifically for the adopted chemical mixtures. Thetracks were extended to the tip of the giant branch or to an age of 30Gyr, whichever came first, and zero-age horizontal-branch (ZAHB) lociwere constructed using the helium core masses and chemical profiles fromappropriate red giant precursors. Selected models have been comparedwith those computed by A. V. Sweigart, for the same masses and chemicalcompositions, to demonstrate that the results obtained from two entirelyindependent stellar evolution codes agree well with one another whenvery similar input physics is assumed. In the case of extremelymetal-deficient stars, an enhancement in the abundance of theα-elements causes a single, fairly significant bump in the opacityat a temperature just above 106 K, which is caused byabsorption processes involving the K shell of oxygen. This peak becomessteadily more pronounced as the overall metallicity increases and asecond bump, arising from the L edges of Ne, Mg, and Si, eventuallyappears near logT=5.6. As far as the tracks and isochrones areconcerned, we find that, as already reported by others, it is possibleto mimic the computations for [α/Fe]>0 remarkably well by thosefor scaled-solar mixes simply by requiring the total mass-fractionabundance of the heavy elements, Z, to be the same. However, this resultholds only for metallicities significantly less than solar. Above[Fe/H]>~-0.8, tracks and isochrones for enhanced α-elementmixtures begin to have systematically hotter/bluer turnoffs and redgiant branches than those for scaled-solar mixtures of the heavyelements. Also addressed is the extent to which our models satisfy theconstraints posed by the local subdwarfs, the distances of which arebased on Hipparcos parallax measurements. Our analysis suggests that thepredicted metallicity dependence of the location of the lower mainsequence on the C-M diagram is in good agreement with the observeddependence. In fact, we do not find any compelling evidence from thelocal Population II calibrators that the colors of our models requiresignificant adjustments. In further support of our calculations, we findthat, both in zero point and slope, the computed giant branches on the(Mbol,logTeff)-plane agree well with thoseinferred for globular clusters from observations in the infrared.Moreover, our ZAHB models have luminosities that are just outside the 1σ error bars of the mean MV's inferred for RR Lyraestars from Baade-Wesselink, statistical parallax, and trigonometricparallax studies. Lower helium contents or higher α-elementabundances or an increase in the conductive opacities are among thepossible ways of reducing the differences that remain. To facilitatecomparisons with observations, the tracks/ZAHBs are provided withpredicted BV(RI)C photometry.
| Abundances and Kinematics of Field Halo and Disk Stars. I. Observational Data and Abundance Analysis
We describe observations and abundance analysis of a high-resolution,high signal-to-noise ratio survey of 168 stars, most of which aremetal-poor dwarfs. We follow a self-consistent LTE analysis technique todetermine the stellar parameters and abundances, and we estimate theeffects of random and systematic uncertainties on the resultingabundances. Element-to-iron ratios are derived for key α-, odd-Z,Fe-peak, and r- and s-process elements. Effects of non-LTE on theanalysis of Fe I lines are shown to be very small on average.Spectroscopically determined surface gravities are derived that arequite close to those obtained from Hipparcos parallaxes.
| 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.
| HIPPARCOS subdwarf parallaxes - Metal-rich clusters and the thick disk
We have used main-sequence fitting to calibrate the distances to theglobular clusters NGC 6397, M5, NGC 288, M71, and 47 Tucanae, matchingthe cluster photometry against data for subdwarfs with precise Hipparcosparallax measurements and accurate abundance determinations. Both thecluster and subdwarf abundance scales are tied to high-resolutionspectroscopic analyses. The distance moduli that we derive for the fiveclusters are 12.24, 14.52, 15.00, 13.19, and 13.59 mag, withuncertainties of 0.15 mag. These distances are higher than those derivedin pre-Hipparcos investigations. The calibrated cluster color-magnitudediagrams provide fiducial sequences in the (MV, B - V)-plane, outliningthe distribution expected for stars of a particular abundance. We havecombined the photometric data for NGC 6397, M5, and 47 Tucanae with themean color-magnitude relation delineated by nearby FGK dwarfs to definea reference grid in the (MV, B - V)-plane, and we have matched this gridagainst data for stars drawn from the Lowell Proper Motion Survey.Limiting the comparison to nonbinaries, there are significantly fewersubluminous stars than expected given the spectroscopic metallicitydistribution. Inverting the analysis, this implies a reduction by afactor of three in the proportion of stars contributing to themetal-poor tail of the Galactic disk. We discuss the implications ofthese results.
| 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
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| Yükselim: | +06°00'51.6" |
| Görünürdeki Parlaklýk: | 8.374 |
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| özdevim Sað Açýklýk: | -465.7 |
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