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Halo Star Streams in the Solar Neighborhood
We have assembled a sample of halo stars in the solar neighborhood tolook for halo substructure in velocity and angular momentum space. Oursample (231 stars) includes red giants, RR Lyrae variable stars, and redhorizontal branch stars within 2.5 kpc of the Sun with [Fe/H] less than-1.0. It was chosen to include stars with accurate distances, spacevelocities, and metallicities, as well as well-quantified errors. Withour data set, we confirm the existence of the streams found by Helmi andcoworkers, which we refer to as the H99 streams. These streams have adouble-peaked velocity distribution in the z-direction (out of theGalactic plane). We use the results of modeling of the H99 streams byHelmi and collaborators to test how one might use vz velocityinformation and radial velocity information to detect kinematicsubstructure in the halo. We find that detecting the H99 streams withradial velocities alone would require a large sample (e.g.,approximately 150 stars within 2 kpc of the Sun and within 20° ofthe Galactic poles). In addition, we use the velocity distribution ofthe H99 streams to estimate their age. From our model of the progenitorof the H99 streams, we determine that it was accreted between 6 and 9Gyr ago. The H99 streams have [α/Fe] abundances similar to otherhalo stars in the solar neighborhood, suggesting that the gas thatformed these stars were enriched mostly by Type II supernovae. We havealso discovered in angular momentum space two other possiblesubstructures, which we refer to as the retrograde and progradeoutliers. The retrograde outliers are likely to be halo substructure,but the prograde outliers are most likely part of the smooth halo. Theretrograde outliers have significant structure in the vφdirection and show a range of [α/Fe], with two having low[α/Fe] for their [Fe/H]. The fraction of substructure stars in oursample is between 5% and 7%. The methods presented in this paper can beused to exploit the kinematic information present in future largedatabases like RAVE, SDSS-II/SEGUE, and Gaia.
| 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.
| The lithium content of the Galactic Halo stars
Thanks to the accurate determination of the baryon density of theuniverse by the recent cosmic microwave background experiments, updatedpredictions of the standard model of Big Bang nucleosynthesis now yieldthe initial abundance of the primordial light elements withunprecedented precision. In the case of ^7Li, the CMB+SBBN value issignificantly higher than the generally reported abundances for Pop IIstars along the so-called Spite plateau. In view of the crucialimportance of this disagreement, which has cosmological, galactic andstellar implications, we decided to tackle the most critical issues ofthe problem by revisiting a large sample of literature Li data in halostars that we assembled following some strict selection criteria on thequality of the original analyses. In the first part of the paper wefocus on the systematic uncertainties affecting the determination of theLi abundances, one of our main goal being to look for the "highestobservational accuracy achievable" for one of the largest sets of Liabundances ever assembled. We explore in great detail the temperaturescale issue with a special emphasis on reddening. We derive four sets ofeffective temperatures by applying the same colour {T}_eff calibrationbut making four different assumptions about reddening and determine theLTE lithium values for each of them. We compute the NLTE corrections andapply them to the LTE lithium abundances. We then focus on our "best"(i.e. most consistent) set of temperatures in order to discuss theinferred mean Li value and dispersion in several {T}_eff and metallicityintervals. The resulting mean Li values along the plateau for [Fe/H]≤ 1.5 are A(Li)_NLTE = 2.214±0.093 and 2.224±0.075when the lowest effective temperature considered is taken equal to 5700K and 6000 K respectively. This is a factor of 2.48 to 2.81 (dependingon the adopted SBBN model and on the effective temperature range chosento delimit the plateau) lower than the CMB+SBBN determination. We findno evidence of intrinsic dispersion. Assuming the correctness of theCMB+SBBN prediction, we are then left with the conclusion that the Liabundance along the plateau is not the pristine one, but that halo starshave undergone surface depletion during their evolution. In the secondpart of the paper we further dissect our sample in search of newconstraints on Li depletion in halo stars. By means of the Hipparcosparallaxes, we derive the evolutionary status of each of our samplestars, and re-discuss our derived Li abundances. A very surprisingresult emerges for the first time from this examination. Namely, themean Li value as well as the dispersion appear to be lower (althoughfully compatible within the errors) for the dwarfs than for the turnoffand subgiant stars. For our most homogeneous dwarfs-only sample with[Fe/H] ≤ 1.5, the mean Li abundances are A(L)_NLTE = 2.177±0.071 and 2.215±0.074 when the lowest effective temperatureconsidered is taken equal to 5700 K and 6000 K respectively. This is afactor of 2.52 to 3.06 (depending on the selected range in {T}_eff forthe plateau and on the SBBN predictions we compare to) lower than theCMB+SBBN primordial value. Instead, for the post-main sequence stars thecorresponding values are 2.260±0.1 and 2.235±0.077, whichcorrespond to a depletion factor of 2.28 to 2.52. These results,together with the finding that all the stars with Li abnormalities(strong deficiency or high content) lie on or originate from the hotside of the plateau, lead us to suggest that the most massive of thehalo stars have had a slightly different Li history than their lessmassive contemporaries. In turn, this puts strong new constraints on thepossible depletion mechanisms and reinforces Li as a stellartomographer.
| Structure in the motions of the fastest halo stars
We analyzed the catalog published by Beers et al. (2000, ApJ, 119, 2866)of 2106 non-kinematically selected metal poor stars in the solarneighborhood, with the goal of quantifying the amount of substructure inthe motions of the fastest halo stars. We computed the two-pointvelocity correlation function for a subsample of halo stars within 1-2kpc of the Sun, and found statistical evidence of substructure with asimilar amplitude to that predicted by high resolution CDM simulations.The signal is due to a small kinematic group whose dynamical propertiesare compared to the stellar "stream" previously discovered by Helmi etal. (1999). If real, this high velocity moving group would providefurther support for the idea that substructures remain as fossils fromthe formation of the Galaxy as expected in the CDM scenario.
| 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.
| 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
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities(vsini) of a sample of 45 candidate field horizontal-branch (HB) starsspanning a wide range of effective temperatures, from red HB stars withTeff~=5000K to blue HB stars with Teff of 17,000K.Among the cooler blue HB stars (Teff=7500-11500 K), weconfirm prior studies showing that, although a majority of stars rotateat vsini<15kms-1, there exists a subset of ``fastrotators'' with vsini as high as 30-35 km s-1. All but one ofthe red HB stars in our sample have vsini<10kms-1, and noanalogous rotation bimodality is evident. We also identify anarrow-lined hot star (Teff~=16,000K) with enhancedphotospheric metal abundances and helium depletion, similar to theabundance patterns found among hot BHB stars in globular clusters, andfour other stars that may also belong in this category. We discussdetails of the spectral line fitting procedure that we use to deducevsini and explore how measurements of field HB star rotation may shedlight on the issue of HB star rotation in globular clusters.
| Spectroscopic Binaries, Velocity Jitter, and Rotation in Field Metal-poor Red Giant and Red Horizontal-Branch Stars
We summarize 2007 radial velocity measurements of 91 metal-poor fieldred giants. Excluding binary systems with orbital solutions, ourcoverage averages 13.7 yr per star, with a maximum of 18.0 yr. We reportfour significant findings. (1) Sixteen stars are found to bespectroscopic binaries, and we present orbital solutions for 14 of them.The spectroscopic binary frequency of the metal-poor red giants, with[Fe/H]<=-1.4, for periods less than 6000 days, is 16%+/-4%, which isnot significantly different from that of comparable-metallicity fielddwarfs, 17%+/-2%. The two CH stars in our program, BD -1°2582 and HD135148, are both spectroscopic binaries. (2) Velocity jitter is presentamong about 40% of the giants with MV<=-1.4. The twobest-observed cases, HD 3008 and BD +22°2411, showpseudoperiodicities of 172 and 186 days, longer than any knownlong-period variable in metal-poor globular clusters. Photometricvariability seen in HD 3008 and three other stars showing velocityjitter hints that starspots are the cause. However, the phasing of thevelocity data with the photometry data from Hipparcos is not consistentwith a simple starspot model for HD 3008. We argue against orbitalmotion effects and radial pulsation, so rotational modulation remainsthe best explanation. The implied rotational velocities for HD 3008 andBD +22°2411, both with MV<=-1.4 and R~50Rsolar, exceed 12 km s-1. (3) Including HD 3008and BD +22°2411, we have found signs of significant excess linebroadening in eight of the 17 red giants with MV<=-1.4,which we interpret as rotation. In three cases, BD +30°2034, CD-37°14010, and HD 218732, the rotation is probably induced by tidallocking between axial rotation and the observed orbital motion with astellar companion. But this cannot explain the other five stars in oursample that display signs of significant rotation. This high frequencyof elevated rotational velocities does not appear to be caused bystellar mass transfer or mergers: there are too few main-sequencebinaries with short enough periods. We also note that the lack of anynoticeable increase in mean rotation at the magnitude level of the redgiant branch luminosity function ``bump'' argues against the rapidrotation's being caused by the transport of internal angular momentum tothe surface. Capture of a planetary-mass companion as a red giantexpands in radius could explain the high rotational velocities. (4) Wealso find significant rotation in at least six of the roughly 15 (40%)red horizontal-branch stars in our survey. It is likely that theenhanced rotation seen among a significant fraction of both blue and redhorizontal-branch stars arose when these stars were luminous red giants.Rapid rotation alone therefore appears insufficient cause to populatethe blue side of the horizontal branch. While the largest projectedrotational velocities seen among field blue and red horizontal-branchstars are consistent with their different sizes, neither are consistentwith the large values we find for the largest red giants. This suggeststhat some form of angular momentum loss (and possibly mass loss) hasbeen at work. Also puzzling is the apparent absence of rotation seen infield RR Lyrae variables. Angular momentum transfer and conservation inevolved metal-poor field stars thus pose many interesting questions forthe evolution of low-mass stars.
| The r-Process in the Early Galaxy
We report Sr, Pd, and Ag abundances for a sample of metal-poor fieldgiants and analyze a larger sample of Y, Zr, and Ba abundances. The[Y/Zr] and [Pd/Ag] abundance ratios are similar to those measured forthe r-process-rich stars CS 22892-052 and CS 31082-001. The [Pd/Ag]ratio is larger than predicted from the solar system r-processabundances. The constant [Y/Zr] and [Sr/Y] values in the field starsplace strong limits on the contributions of the weak s-process and themain s-process to the light neutron-capture elements. Stars in theglobular cluster M15 possess lower [Y/Zr] values than the field stars.There is a large dispersion in [Y/Ba]. Because the r-process isresponsible for the production of the heavy elements in the earlyGalaxy, these dispersions require varying light-to-heavy ratios inr-process yields.
| Abundances of 30 Elements in 23 Metal-Poor Stars
We report the abundances of 30 elements in 23 metal-poor([Fe/H]<-1.7) giants. These are based on 7774 equivalent widths andspectral synthesis of 229 additional lines. Hyperfine splitting is takeninto account when appropriate. Our choice of model atmospheres has themost influence on the accuracy of our abundances. We consider the effectof different model atmospheres on our results. In addition to the randomerrors in Teff, logg, and microturbulent velocity, there areseveral sources of systematic error. These include using Teffdetermined from Fe I lines rather than colors, ignoring non-LTE effectson the Fe I/Fe II ionization balance, using models with solar[α/Fe] ratios, and using Kurucz models with overshooting. Ofthese, only the use of models with solar [α/Fe] ratios had anegligible effect. However, while the absolute abundances can change bygreater than 0.10 dex, the relative abundances, especially betweenclosely allied atoms such as the rare earth group, often show only small(less than 0.03 dex) changes. We found that some strong lines of Fe I,Mn I, and Cr I consistently gave lower abundances by ~0.2 dex, a numberlarger than the quoted errors in the gf-values. After considering amodel with depth-dependent microturbulent velocity and a model withhotter temperatures in the upper layers, we conclude that the latter dida better job of resolving the problem and agreeing with observationalevidence for the structure of stars. The error analysis includes theeffects of correlation of Teff, logg, and ξ errors, whichis crucial for certain element ratios, such as [Mg/Fe]. The abundancespresented here are being analyzed and discussed in a separate series ofpapers.
| Three-dimensional Spectral Classification of Low-Metallicity Stars Using Artificial Neural Networks
We explore the application of artificial neural networks (ANNs) for theestimation of atmospheric parameters (Teff, logg, and [Fe/H])for Galactic F- and G-type stars. The ANNs are fed withmedium-resolution (Δλ~1-2 Å) non-flux-calibratedspectroscopic observations. From a sample of 279 stars with previoushigh-resolution determinations of metallicity and a set of (external)estimates of temperature and surface gravity, our ANNs are able topredict Teff with an accuracy ofσ(Teff)=135-150 K over the range4250<=Teff<=6500 K, logg with an accuracy ofσ(logg)=0.25-0.30 dex over the range 1.0<=logg<=5.0 dex, and[Fe/H] with an accuracy σ([Fe/H])=0.15-0.20 dex over the range-4.0<=[Fe/H]<=0.3. Such accuracies are competitive with theresults obtained by fine analysis of high-resolution spectra. It isnoteworthy that the ANNs are able to obtain these results withoutconsideration of photometric information for these stars. We have alsoexplored the impact of the signal-to-noise ratio (S/N) on the behaviorof ANNs and conclude that, when analyzed with ANNs trained on spectra ofcommensurate S/N, it is possible to extract physical parameter estimatesof similar accuracy with stellar spectra having S/N as low as 13. Takentogether, these results indicate that the ANN approach should be ofprimary importance for use in present and future large-scalespectroscopic surveys.
| Th Ages for Metal-poor Stars
With a sample of 22 metal-poor stars, we demonstrate that theheavy-element abundance pattern (Z>=56) is the same as the r-processcontributions to the solar nebula. This bolsters the results of previousstudies that there is a universal r-process production pattern. We usethe abundance of thorium in five metal-poor stars, along with anestimate of the initial Th abundance based on the abundances of stabler-process elements, to measure their ages. We have four field red giantswith errors of 4.2 Gyr in their ages and one M92 giant with an error of5.6 Gyr, based on considering the sources of observational error only.We obtain an average age of 11.4 Gyr, which depends critically on theassumption of an initial Th/Eu production ratio of 0.496. If theuniverse is 15 Gyr old, then the (Th/Eu)0 should be 0.590, inagreement with some theoretical models of the r-process.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars
We present a detailed analysis of the space motions of 1203solar-neighborhood stars with metal abundances [Fe/H]<=-0.6, on thebasis of a catalog, of metal-poor stars selected without kinematic biasrecently revised and supplemented by Beers et al. This sample, havingavailable proper motions, radial velocities, and distance estimates forstars with a wide range of metal abundances, is by far the largest suchcatalog to be assembled to date. We show that the stars in our samplewith [Fe/H]<=-2.2, which likely represent a ``pure'' halo component,are characterized by a radially elongated velocity ellipsoid(σU,σV,σW)=(141+/-11,106+/-9, 94+/-8) km s-1 and small prograde rotation=30 to 50 km s-1, consistent withprevious analysis of this sample by Beers and Sommer-Larsen based onradial velocity information alone. In contrast to the previous analysis,we find a decrease in with increasingdistance from the Galactic plane for stars that are likely to be membersof the halo population(Δ/Δ|Z|=-52+/-6 km s-1kpc-1), which may represent the signature of a dissipativelyformed flattened inner halo. Unlike essentially all previouskinematically selected catalogs, the metal-poor stars in our sampleexhibit a diverse distribution of orbital eccentricities, e, with noapparent correlation between [Fe/H] and e. This demonstrates, clearlyand convincingly, that the evidence offered in 1962 by Eggen,Lynden-Bell, & Sandage for a rapid collapse of the Galaxy, anapparent correlation between the orbital eccentricity of halo stars withmetallicity, is basically the result of their proper-motion selectionbias. However, even in our nonkinematically selected sample, we haveidentified a small concentration of high-e stars at [Fe/H]~-1.7, whichmay originate, in part, from infalling gas during the early formation ofthe Galaxy. We find no evidence for an additional thick disk componentfor stellar abundances [Fe/H]<=-2.2. The kinematics of theintermediate-abundance stars close to the Galactic plane are, in part,affected by the presence of a rapidly rotating thick disk component with ~=200 km s-1 (with a verticalvelocity gradient on the order ofΔ/Δ|Z|=-30+/-3 km s-1kpc-1) and velocity ellipsoid (σU,σV, σW)=(46+/-4, 50+/-4, 35+/-3) kms-1. The fraction of low-metallicity stars in the solarneighborhood that are members of the thick disk population is estimatedas ~10% for -2.2<[Fe/H]<=-1.7 and ~30% for -1.7<[Fe/H]<=-1.We obtain an estimate of the radial scale length of the metal-weak thickdisk of 4.5+/-0.6 kpc. We also analyze the global kinematics of thestars constituting the halo component of the Galaxy. The outer part ofthe halo, which we take to be represented by local stars on orbitsreaching more than 5 kpc from the Galactic plane, exhibits no systematicrotation. In particular, we show that previous suggestions of thepresence of a ``counter-rotating high halo'' are not supported by ouranalysis. The density distribution of the outer halo is nearly sphericaland exhibits a power-law profile that is accurately described asρ~R-3.55+/-0.13. The inner part of the halo ischaracterized by a prograde rotation and a highly flattened densitydistribution. We find no distinct boundary between the inner and outerhalo. We confirm the clumping in angular-momentum phase space of a smallnumber of local metal-poor stars noted in 1999 by Helmi et al. We alsoidentify an additional elongated feature in angular-momentum phase spaceextending from the clump to regions with high azimuthal rotation. Thenumber of members in the detected clump is not significantly increasedfrom that reported by Helmi et al., even though the total number of thesample stars we consider is almost triple that of the previousinvestigation. We conclude that the fraction of halo stars that may havearisen from the precursor object of this clump may be smaller than 10%of the present Galactic halo, as previously suggested. The implicationsof our results for the formation of the Galaxy are discussed, inparticular in the context of the currently favored cold dark mattertheory of hierarchical galaxy formation.
| The effective temperature scale of giant stars (F0-K5). I. The effective temperature determination by means of the IRFM
We have applied the InfraRed Flux Method (IRFM) to a sample ofapproximately 500 giant stars in order to derive their effectivetemperatures with an internal mean accuracy of about 1.5% and a maximumuncertainty in the zero point of the order of 0.9%. For the applicationof the IRFM, we have used a homogeneous grid of theoretical modelatmosphere flux distributions developed by \cite[Kurucz (1993)]{K93}.The atmospheric parameters of the stars roughly cover the ranges: 3500 K<= T_eff <= 8000 K; -3.0 <= [Fe/H] <= +0.5; 0.5 <= log(g) <= 3.5. The monochromatic infrared fluxes at the continuum arebased on recent photometry with errors that satisfy the accuracyrequirements of the work. We have derived the bolometric correction ofgiant stars by using a new calibration which takes the effect ofmetallicity into account. Direct spectroscopic determinations ofmetallicity have been adopted where available, although estimates basedon photometric calibrations have been considered for some stars lackingspectroscopic ones. The adopted infrared absolute flux calibration,based on direct optical measurements of stellar angular diameters, putsthe effective temperatures determined in this work in the same scale asthose obtained by direct methods. We have derived up to fourtemperatures, TJ, TH, TK and T_{L'},for each star using the monochromatic fluxes at different infraredwavelengths in the photometric bands J, H, K and L'. They show goodconsistency over 4000 K, and there is no appreciable trend withwavelength, metallicity and/or temperature. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of error and their effect on final temperatures. Wealso provide a comparison of the results with previous work.
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| Ca II H and K Photometry on the UVBY System. III. The Metallicity Calibration for the Red Giants
New photometry on the uvby Ca system is presented for over 300 stars.When combined with previous data, the sample is used to calibrate themetallicity dependence of the hk index for cooler, evolved stars. Themetallicity scale is based upon the standardized merger of spectroscopicabundances from 38 studies since 1983, providing an overlap of 122evolved stars with the photometric catalog. The hk index producesreliable abundances for stars in the [Fe/H] range from -0.8 to -3.4,losing sensitivity among cooler stars due to saturation effects athigher [Fe/H], as expected.
| Broad-band JHK(L') photometry of a sample of giants with 0.5 > [Fe/H] > -3
We present the results of a three-year campaign of broad-band photometryin the near-infrared J, H, K and L' bands for a sample of approximately250 giant stars carried out at the Observatorio del Teide (Tenerife,Spain). Transformations of the Telescopio Carlos Sanchez systeminto/from several currently used infrared systems are extended to theredward part of the colour axis. The linearity of our photometric systemin the range -3 mag [Fe/H] >-3. Data of comparable quality previouslypublished have been added to the sample in order to increase thereliability of the relations to be obtained. We also provide mean IRcolours for giant stars according to spectral type.ables 1, 2 and 3 are only available in electronic form via the CDS(anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| 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
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| 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
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| The abundance of lithium in metal-poor subgiant stars
We have determined lithium abundances for a sample of 79 halo subgiants.The subgiant candidates were identified using uvby photometry fromseveral catalogs of metal-poor stars. The basic data werehigh-resolution, low-noise coude spectra in the 6700 A spectral region.Abundances of iron and calcium, derived from one Ca I and several Fe Ilines in our spectra, provided a metallicity discriminant for the starsin our sample. The subgiants with temperatures between 5500 and 4900 Kshow a steady decline of lithium abundance with advancing subgiantposition (and decreasing temperature). The observed trend is inqualitative agreement with recent theoretical models of lithium dilutionin metal-poor stars, especially if main-sequence diffusion is included.The initial lithium abundances in metal-poor stars may have beenslightly larger than that exhibited by stars near the main-sequenceturnoff. For stars with temperatures below 4900 K, the models predict nofurther dilution, but observed lithium abundances continue to declinewith decreasing temperature, indicating further lithium destruction onthe giant branch of metal-poor stars. In all postdilution subgiants, theobserved lithium abundances show more scatter than do stars at themain-sequence turnoff, suggesting variations in the main-sequencelithium destruction below the observable surface layers.
| Armchair cartography - A map of the Galactic halo based on observations of local, metal-poor stars
The velocity distribution of metal-poor halo stars in the solarneighborhood is studied to extract data on the global spatial andkinematic properties of the Galactic stellar halo. A global model of thesolar neighborhood stars is constructed from observed positions andthree-dimensional velocity of local, metal-poor halo stars in terms of adiscrete sum of orbits. The characteristics of the reconstructed haloare examined and used to study the evolution of the halo subsystems.
| Calcium abundances in atmospheres of 43 G and K giants
Not Available
| Determination of effective temperatures and surface gravities of metal-deficient K-G giants in the Vilnius photometric system
Not Available
| Three-dimensional classification of 78 metal-deficient giants in the Vinius photometric system
Not Available
| The kinematics of halo red giants
The present 337 radial velocities were obtained with typical accuraciesof 0.7 cm km/sec for 85 metal-poor field red giants, selected from thekinematically unbiased samples of Bond (1980) and Bidelman and MacConnel(1973). The multiply-observed stars suggest the field halo binaryfraction exceeds 10 percent. Using these velocities and those publishedby others, a sample of 174 red giants with Fe/H of not more than -1.5 isobtained. Their mean motion with respect to the local standard of restis -206 + or - 23 km/sec, and the velocity dispersions are sigma (R) of154 + or - 18 km/sec, sigma(theta) of 102 + or - 27 km/sec, andsigma(phi) of 107 + or - 15 km/sec. Using photometrically derivedabsolute magnitudes and published proper motions, orbital eccentricitiesare computed for 72 stars not already considered in a similar study ofsouthern stars by Norris et al. (1985). A few stars with e of less than0.4 are found.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Virgo |
| Ascensió Recta: | 12h59m19.93s |
| Declinació: | +09°14'35.6" |
| Magnitud Aparent: | 9.736 |
| Moviment propi RA: | -44.3 |
| Moviment propi Dec: | 28.8 |
| B-T magnitude: | 10.605 |
| V-T magnitude: | 9.808 |
Catàlegs i designacions:
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