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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 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
| 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
| 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
| 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.
| 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
| 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.
| 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.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| 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.
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Metal-poor subdwarfs and early galactic nucleosynthesis
Observations of more than 20 metal-poor subdwarfs are presented,discussing the spectroscopic abundance analyses based on high-reolutionspectra and scaled solar model atmospheres. Many of the stars are shownto be more evolved than can be reconciled with reasonable time scalesbased on standard theory of stellar evolution, suggesting that the postmain sequence evolution of cool metal-poor stars is influenced by anenhanced O/Fe ratio compared with a standard solar mixture. Radialvelocities are given for 60 metal-poor stars, 25 percent of which aresuspected to be velocity variable. The kinematic properties of severalspecific stars are discussed. The abundance ratios Mg/Fe, Ca/Fe, Ti/Fe,Al/Fe, and Mn/Fe as a function of the Fe abundance itself indicate thatthese elements probably have not been produced in purely explosivenucleosynthesis. It is suggested that a considerable fraction of theisotopes must have been synthesized during preceding hydrostatic burningphases.
| Population studies. I - The Bidelman-MacConnell 'weak-metal' stars
BRVI and DDO photometry are presented for 309 Bidelman-MacConnell'weak-metal' stars. Radial velocities are calculated for most of thestars having Fe/H abundances of no more than -0.8. The photometricobservations were carried out using the 0.6-meter and 1.0-metertelescopes of the Siding Spring Observatory. Photometric taxonomy wasused to classify the stars as dwarfs, giants, red-horizontal branchstars, and ultraviolet-bright stars, respectively. It is found that 35percent of the stars are giants; 50 percent are dwarfs; and 5 percentbelong to the red-horizontal branch group. The role of selection effectsin investigations of the formation of the Galaxy is discussed on thebasis of the photometric observations and the observational constraintsproposed by Eggen et al. (1962).
| Southern metal-poor stars - UBVRI photometry
Considering the study of subdwarf kinematics and metallicities by Eggen,Lynden-Bell, and Sandage (1962), UBVRI photometry and normalizedultraviolet excesses are presented for 178 metal-poor stars, 144 ofwhich are contained in the kinematically unbiased list of Bidelman andMacConnell (1973). The Lowell 0.6 m telescope at Cerro Tololo was used,equipped with a single-channel photometer and a Ga-As photomultiplier.The final magnitudes and colors, number of observations, value ofdelta(U-B)0.6 (if B-V lies between 0.35 and 0.90), B and M class, andpublished spectral types for these stars are presented; severalextremely metal-poor stars are evident. In addition, sixteen nearbyvisual companions of the stars were measured, and their magnitudes andcolors are given.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Киль |
| Прямое восхождение: | 10h30m04.61s |
| Склонение: | -71°33'39.2" |
| Видимая звёздная величина: | 9.066 |
| Собственное движение RA: | -131.9 |
| Собственное движение Dec: | 53 |
| B-T magnitude: | 9.726 |
| V-T magnitude: | 9.121 |
Каталоги и обозначения:
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