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Two distinct halo populations in the solar neighborhood. III. Evidence from stellar ages and orbital parameters
Context. In Papers I and II of this series, we have found clearindications of the existence of two distinct populations of stars in thesolar neighborhood belonging to the metal-rich end of the halometallicity distribution function. Based on high-resolution, high S/Nspectra, it is possible to distinguish between "high-alpha" and"low-alpha" components using the [?/Fe] versus [Fe/H] diagram. Aims: Precise relative ages and orbital parameters are determined for67 halo and 16 thick-disk stars having metallicities in the range -1.4< [Fe/H] < -0.4 to better understand the context of the two halopopulations in the formation and evolution of the Galaxy. Methods: Ages are derived by comparing the positions of stars in the logTeff-log g diagram with isochrones from the Y2models interpolated to the exact [Fe/H] and [?/Fe] values of eachstar. The stellar parameters have been adopted from the precedingspectroscopic analyses, but possible systematic errors inTeff and log g are considered and corrected. With spacevelocities from Paper I as initial conditions, orbital integrations havebeen carried out using a detailed, observationally constrainedMilky Way model including a bar and spiral arms. Results: The "high-alpha" halo stars have ages 2-3 Gyr larger thanthe "low-alpha" ones, with some probability that the thick-disk starshave ages intermediate between these two halo components. The orbitalparameters show very distinct differences between the "high-alpha" and"low-alpha" halo stars. The "low-alpha" ones have rmax's to30-40 kpc, zmax's to ?18 kpc, and emax'sclumped at values greater than 0.85, while the "high-alpha" ones,rmax's to about 16 kpc, zmax's to 6-8 kpc, andemax values more or less uniformly distributed over 0.4-1.0. Conclusions: A dual in situ-plus-accretion formation scenariobest explains the existence and characteristics of these two metal-richhalo populations, but one remaining defect is that this model is notconsistent regarding the rmax's obtained for the in situ"high-alpha" component; the predicted values are too small. It appearsthat ? Cen may have contributed in asignificant way to the existence of the "low-alpha" component; recentmodels, including dynamical friction and tidal stripping, have producedresults consistent with the present mass and orbital characteristics of? Cen, while at the same time includingextremes in the orbital parameters as great as those of the "low-alpha"component.Based on observations made with the Nordic Optical Telescope on LaPalma, and on data from the European Southern Observatory ESO/ST-ECFScience Archive Facility (programmes 65.L-0507, 67.D-0086, 67.D-0439,68.D-0094, 68.B-0475, 69.D-0679, 70.D-0474, 71.B-0529, 72.B-0585,76.B-0133 and 77.B-0507).Tables 1 and 4 are available in electronic format http://www.aanda.org.
| Beryllium and Alpha-element Abundances in a Large Sample of Metal-poor Stars
The light elements, Li, Be, and B, provide tracers for many aspects ofastronomy including stellar structure, Galactic evolution, andcosmology. We have made observations of Be in 117 metal-poor starsranging in metallicity from [Fe/H] = -0.5 to -3.5 with KeckI/HIRES. Our spectra are high resolution (~42,000) and high signal tonoise (the median is 106 per pixel). We have determined the stellarparameters spectroscopically from lines of Fe I, Fe II, Ti I, and Ti II.The abundances of Be and O were derived by spectrum synthesistechniques, while abundances of Fe, Ti, and Mg were found from manyspectral line measurements. There is a linear relationship between[Fe/H] and A(Be) with a slope of +0.88 ± 0.03 over three ordersof magnitude in [Fe/H]. We find that Be is enhanced relative to Fe;[Be/Fe] is +0.40 near [Fe/H] ~-3.3 and drops to 0.0 near [Fe/H]~-1.7. For the relationship between A(Be) and [O/H], we find agradual change in slope from 0.69 ± 0.13 for the Be-poor/O-poorstars to 1.13 ± 0.10 for the Be-rich/O-rich stars. Inasmuch asthe relationship between [Fe/H] and [O/H] seems robustly linear (slope =+0.75 ± 0.03), we conclude that the slope change in Be versus Ois due to the Be abundance. Much of the Be would have been formed in thevicinity of Type II supernova (SN II) in the early history of the Galaxyand by Galactic cosmic-ray (GCR) spallation in the later eras. AlthoughBe is a by-product of CNO, we have used Ti and Mg abundances asalpha-element surrogates for O in part because O abundances are rathersensitive to both stellar temperature and surface gravity. We find thatA(Be) tracks [Ti/H] very well with a slope of 1.00 ± 0.04. Italso tracks [Mg/H] very well with a slope of 0.88 ± 0.03. We havekinematic information on 114 stars in our sample and they divide equallyinto dissipative and accretive stars. Almost the full range of [Fe/H]and [O/H] is covered in each group. There are distinct differences inthe relationships of A(Be) and [Fe/H] and of A(Be) and [O/H] for thedissipative and the accretive stars. It is likely that the formation ofBe in the accretive stars was primarily in the vicinity of SN II, whilethe Be in the dissipative stars was primarily formed by GCR spallation.We find that Be is not as good a cosmochronometer as Fe. We have found aspread in A(Be) that is valid at the 4? level between [O/H] =-0.5 and -1.0, which corresponds to -0.9 and-1.6 in [Fe/H].
| Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
Context. Current models of galaxy formation predict that the Galactichalo was assembled hierarchically. By measuring abundance ratios instars it may be possible to identify substructures in the halo resultingfrom this process. Aims: A previous study of 94 dwarf stars with-1.6 < [Fe/H] < -0.4 in the solar neighborhood has revealed theexistence of two distinct halo populations with a systematic differencein [?/Fe] at a given metallicity. In continuation of that work,abundances of Mn, Cu, Zn, Y, and Ba are determined for the same sampleof stars. Methods: Equivalent widths of atomic lines are measuredfrom high resolution VLT/UVES and NOT/FIES spectra and used to deriveabundance ratios from an LTE analysis based on MARCS model atmospheres.The analysis is made relative to two thick-disk stars, HD22879 and HD 76932, such that very precisedifferential values are obtained. Results: Systematic differencesbetween the "high-?" and "low-?" halo populations are foundfor [Cu/Fe], [Zn/Fe], and [Ba/Y], whereas there is no significantdifference in the case of [Mn/Fe]. At a given metallicity, [Cu/Fe] showsa large scatter that is closely correlated with a corresponding scatterin [Na/Fe] and [Ni/Fe]. Conclusions: The metallicity trends of[Cu/Fe], [Zn/Fe], and [Ba/Y] can be explained from existingnucleosynthesis calculations if the high-? stars formed in regionswith such a high star formation rate that only massive stars and type IIsupernovae contributed to the chemical enrichment. The low-?stars, on the other hand, most likely originate from systems with aslower chemical evolution, characterized by additional enrichment fromtype Ia supernovae and low-mass AGB stars.Based on observations made with the Nordic Optical Telescope on LaPalma, and on data from the European Southern Observatory ESO/ST-ECFScience Archive Facility (programs 65.L-0507, 67.D-0086, 67.D-0439,68.D-0094, 68.B-0475, 69.D-0679, 70.D-0474, 71.B-0529, 72.B-0585,76.B-0133 and 77.B-0507).Tables 1, 2, and excerpt of Table 3 areavailable in electronic form at http://www.aanda.orgTables 1, 2, andfull Table 3 are also available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/530/A15
| The HARPS search for southern extrasolar planets. XXV. Results from the metal-poor sample
Searching for extrasolar planets around stars of different metallicitymay provide strong constraints to the models of planet formation andevolution. In this paper we present the overall results of a HARPS (ahigh-precision spectrograph mostly dedicated to deriving precise radialvelocities) program to search for planets orbiting a sample of 104metal-poor stars (selected [Fe/H] below -0.5). Radial velocity timeseries of each star are presented and searched for signals using severalstatistical diagnostics. Stars with detected signals are presented,including 3 attributed to the presence of previously announced giantplanets orbiting the stars HD 171028, HD 181720, and HD 190984. Severalbinary stars and at least one case of a coherent signal caused byactivity-related phenomena are presented. One very promising new,possible giant planet orbiting the star HD 107094 is discussed, and theresults are analyzed in light of the metallicity-giant planetcorrelation. We conclude that the frequency of giant planets orbitingmetal-poor stars may be higher than previously thought, probablyreflecting the higher precision of the HARPS survey. In the metallicitydomain of our sample, we also find evidence that the frequency ofplanets is a steeply rising function of the stellar metal content, asfound for higher metallicity stars.Based on observations collected at the La Silla Parana Observatory, ESO(Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID72.C-0488, 082.C-0212, and 085.C-0063).Full Tables 1 and 3 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A112
| Spectroscopic characterization of a sample of metal-poor solar-type stars from the HARPS planet search program. Precise spectroscopic parameters and mass estimation
Stellar metallicity strongly correlates with the presence of planets andtheir properties. To check for new correlations between stars and theexistence of an orbiting planet, we determine precise stellar parametersfor a sample of metal-poor solar-type stars. This sample was observedwith the HARPS spectrograph and is part of a program to search for newextrasolar planets. The stellar parameters were determined using an LTEanalysis based on equivalent widths (EW) of iron lines and by imposingexcitation and ionization equilibrium. The ARES code was used to allowautomatic and systematic derivation of the stellar parameters. Precisestellar parameters and metallicities were obtained for 97 lowmetal-content stars. We also present the derived masses, luminosities,and new parallaxes estimations based on the derived parameters, andcompare our spectroscopic parameters with an infra-red flux methodcalibration to check the consistency of our method in metal poor stars.Both methods seems to give the same effective temperature scale. Finallywe present a new calibration for the temperature as a function of B-Vand [Fe/H]. This was obtained by adding these new metal poor stars inorder to increase the range in metallicity for the calibration. Thestandard deviation of this new calibration is ~50 K.Based on observations collected at the La Silla Parana Observatory, ESO(Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID72.C-0488, 082.C-0212, and 085.C-0063).Tables 1-3 are only available inelectronic form at http://www.aanda.org
| The ability of intermediate-band Strömgren photometry to correctly identify dwarf, subgiant, and giant stars and provide stellar metallicities and surface gravities
Context. Several large scale photometric and spectroscopic surveys arebeing undertaken to provide a more detailed picture of the Milky Way.Given the necessity of generalisation in the determination of, e.g.,stellar parameters when tens and hundred of thousands of stars areconsidered it remains important to provide independent, detailed studiesto verify the methods used in the surveys. Aims: Our first aim isto critically evaluate available calibrations for deriving [M/H] fromStrömgren photometry. Secondly, we develop the standard sequencesfor dwarf stars to reflect their inherent metallicity dependence.Finally, we test how well metallicities derived from ugriz photometryreproduce metallicities derived from the well-tested system ofStrömgren photometry. Methods: We evaluate availablemetallicity calibrations based on Strömgren uvby photometry fordwarf stars using a catalogue of stars with both uvby photometry andspectroscopically determined iron abundances ([Fe/H]). The catalogue wascreated for this project. Using this catalogue, we also evaluateavailable calibrations that determine log g. A larger catalogue, inwhich metallicity is determined directly from uvby photometry, is usedto trace metallicity-dependent standard sequences for dwarf stars. Wealso perform comparisons, for both dwarf and giant stars, ofmetallicities derived from ugriz photometry with metallicities derivedfrom Strömgren photometry. Results: We provide a homogenisedcatalogue of 451 dwarf stars with 0.3 < (b-y)0 < 1.0.All stars in the catalogue have uvby photometry and [Fe/H] determinedfrom spectra with high resolution and high signal-to-noise ratios (S/N).Using this catalogue, we test how well various photometric metallicitycalibrations reproduce the spectroscopically determined [Fe/H]. Usingthe preferred metallicity calibration for dwarf stars, we derive newstandard sequences in the c1,0 versus (b-y)0 planeand in the c1,0 versus (v-y)0 plane for dwarfstars with 0.40 < (b-y)0 < 0.95 and 1.10 <(v-y)0 < 2.38. Conclusions: We recommend thecalibrations of Ramírez & Meléndez (2005) in derivingmetallicities from Strömgren photometry and find that intermediateband photometry, such as Strömgren photometry, more accurately thanbroad band photometry reproduces spectroscopically determined [Fe/H].Strömgren photometry is also better at differentiating betweendwarf and giant stars. We conclude that additional investigations of thedifferences between metallicities derived from ugriz photometry andintermediate-band photometry, such as Strömgren photometry, arerequired.Appendix A is only available in electronic form at http://www.aanda.org, Appendix B isavailable in electronic form at http://www.aanda.org and at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/521/A40
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Chemical Abundances of Outer Halo Stars in the Milky Way
We present the chemical abundances of 57 metal-poor ([Fe/H] 5 kpc above andbelow the Galactic plane. High-resolution (R ˜ 50000-55000), highsignal-to-noise (S/N > 100) spectra for the sample stars obtainedwith Subaru/HDS were used to derive the chemical abundances of Na, Mg,Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y, and Ba with an LTE abundance analysiscode. The resulting abundance data were combined with those presented inthe literature that mostly targeted at smaller Zmax stars,and both data were used to investigate any systematic trends in detailedabundance patterns depending on their kinematics. It was shown that, inthe metallicity range of ?2 < [Fe/H] < ?1, the [Mg/Fe]ratios for stars with Zmax > 5 kpc are systematicallylower (˜0.1 dex) than those with a smaller Zmax. Forthis metallicity range, a modest degree of depression in the [Si/Fe] andthe [Ca/Fe] ratios was also observed. This result of lower [?/Fe]for the assumed outer halo stars is consistent with previous studiesthat found a signature of lower [?/Fe] ratios for stars withextreme kinematics. The distribution of the [Mg/Fe] ratios for the outerhalo stars partly overlaps with that for stars belonging to the MilkyWay dwarf satellites in the metallicity interval of ?2 < [Fe/H]< ?1 and spans a range intermediate between the distributionsfor the inner halo stars and the stars belonging to the satellites. Ourresults confirm the inhomogeneous nature of the chemical abundanceswithin the Milky Way stellar halo, depending on the kinematic propertiesof the constituent stars, as suggested by earlier studies. Possibleimplications for the formation of the Milky Way halo and its relevanceto the suggested dual nature of the halo are discussed.
| Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
Aims: Precise abundance ratios are determined for 94 dwarf starswith Teff K, -1.6 < [Fe/H] < -0.4, and distances D? 335 pc. Most of them have halo kinematics, but 16 thick-disk starsare included. Methods: Equivalent widths of atomic lines aremeasured from VLT/UVES and NOT/FIES spectra with resolutions R? 55000 and R ? 40 000, respectively. An LTE abundance analysis basedon MARCS models is applied to derive precise differential abundanceratios of Na, Mg, Si, Ca, Ti, Cr, and Ni with respect to Fe. Results: The halo stars fall into two populations, clearly separated in[?/Fe], where ? refers to the average abundance of Mg, Si,Ca, and Ti. Differences in [Na/Fe] and [Ni/Fe] are also present with aremarkably clear correlation between these two abundance ratios. Conclusions: The “high-?” stars may be ancient disk orbulge stars “heated” to halo kinematics by merging satellitegalaxies or they could have formed as the first stars during thecollapse of a proto-Galactic gas cloud. The kinematics of the“low-?” stars suggest that they have been accretedfrom dwarf galaxies, and that some of them may originate from the? Cen progenitor galaxy.Based on observations made with the Nordic Optical Telescope on LaPalma, and on data from the European Southern Observatory ESO/ST-ECFScience Archive Facility.Tables 3 and 4 are also 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/511/L10Figures5-8 and Tables 1-4 are only available in electronic form at http://www.aanda.org
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Kinematics and metallicity analysis for nearby F, G and K stars
A sample containing 1 026 stars of spectral types F, G, and K, mainlydwarfs, from the solar neighbourhood with available space velocities andmetallicities is treated. The treatment comprises a statistical analysisof the metallicity and velocity data and calculation of galactocentricorbits. Sample stars identified as members of the galactic halo aredetached from the rest of the sample based on the values of theirmetallicities, velocity components and galactocentric orbits. Inidentifying halo stars a new, kinematical, criterion is proposed. Exceptone, these halo stars are the metal-poorest ones in the sample. Besides,they have very high velocities with respect to LSR. On the other hand,the separation between the thin disc and thick one is done statisticallybased on LSR space velocities, membership probability (Schwarzschilddistribution with assumed parameters) and galactocentric orbits. In themetallicity these two groups are not much different. For each of thethree subsamples the mean motion and velocity ellipsoid are calculated.The elements of the velocity ellipsoids agree well with the values foundin the literature, especially for the thin disc. The fractions of thesubsystems found for the present sample are: thin disc 93%, thick disc6%, halo 1%. The sample stars established to be members of the thin discare examined for existence of star streams. Traces of both, known andunknown, star streams are not found.
| Speckle interferometry of metal-poor stars in the solar neighborhood. II
The results of speckle interferometric observations of 115 metal-poorstars ([m/H] < ‑1) within 250 pc from the Sun and with propermotions µ ≳ 0.2″/yr, made with the 6-m telescope of theSpecial Astrophysical Observatory of the Russian Academy of Sciences,are reported. Close companions with separations ranging from0.034″ to 1″ were observed for 12 objects—G76-21,G59-1, G63-46, G135-16, G168-42, G141-47, G142-44, G190-10, G28-43,G217-8, G130-7, and G89-14—eight of them are astrometricallyresolved for the first time. The newly resolved systems include onetriple star—G190-10. If combined with spectroscopic and visualdata, our results imply a single:binary:triple:quadruple star ratio of147:64:9:1 for a sample of 221 primary components of halo and thick-diskstars.
| The usage of Strömgren photometry in studies of local group dwarf spheroidal galaxies. Application to Draco: a new catalogue of Draco members and a study of the metallicity distribution function and radial gradients
Aims.In this paper we demonstrate how Strömgren uvby photometry canbe efficiently used to: 1. identify red giant branch stars that aremembers in a dwarf spheroidal galaxy; 2. derive age-independentmetallicities for the same stars and quantify the associated errors. Methods: Strömgren uvby photometry in a 11 × 22 arcmin fieldcentered on the Draco dwarf spheroidal galaxy was obtained using theIsaac Newton Telescope on La Palma. Members of the Draco dSph galaxywere identified using the surface gravity sensitive c1 indexwhich discriminates between red giant and dwarf stars. Thus enabling usto distinguish the (red giant branch) members of the dwarf spheroidalgalaxy from the foreground dwarf stars in our galaxy. The method isevaluated through a comparison of our membership list with membershipclassifications in the literature based on radial velocities and propermotions. The metallicity sensitive m1 index was used toderive individual and age-independent metallicities for the members ofthe Draco dSph galaxy. The derived metallicities are compared to studiesbased on high resolution spectroscopy and the agreement is found to bevery good. Results: We present metallicities for 169 members of the redgiant branch in the Draco dwarf spheroidal galaxy (the largest sample todate). The metallicity distribution function for the Draco dSph galaxyshows a mean [Fe/H] = -1.74 dex with a spread of 0.24 dex. Thecorrelation between metallicity and colour for the stars on the redgiant branch is consistent with a dominant old, and coeval population.There is a possible spatial population gradient over the field with themost metal-rich stars being more centrally concentrated than themetal-poor stars.Based on observations made with the Isaac Newton Telescope, operated onthe Island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. Guest User, Canadian Astronomy Data Centre, which isoperated by the Herzberg Institute of Astrophysics, National ResearchCouncil of Canada. Full Tables 2 and 6 are only available athttp://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Medium resolution spectroscopy in ω Centauri: abundances of 400 subgiant and turn-off region stars
Medium resolution spectra of more than 400 subgiant and turn-off regionstars in ω Centauri were analysed. The observations were performedat the VLT/Paranal with FORS2/MXU. In order to determine themetallicities of the sample stars, we defined a set of line indices(mostly iron) adjusted to the resolution of our spectra. The indices asdetermined for ω Cen were then compared to line indices from starsin the chemically homogeneous globular cluster M 55, in addition tostandard stars and synthetic spectra. The uncertainties in the derivedmetallicities are of the order of ±0.2 {dex}. Our study confirmsthe large variations in iron abundances found on the giant branch inearlier studies (-2.2 <[Fe/H]< -0.7 dex). In addition, we studiedthe α-element and CN/CH abundances. Stars of different metallicitygroups not only show distinct ages (Hilker et al. 2004, A&A, 422,L9), but also different behaviours in their relative abundances. Theα abundances increase smoothly with increasing metallicityresulting in a flat [ α/Fe] ratio over the whole observedmetallicity range. The combined CN+CH abundance increases smoothly withincreasing iron abundance. The most metal-rich stars are CN-enriched. Ina CN vs. CH plot, though, the individual abundances divide into CN- andCH-rich branches. The large abundance variations observed in our sampleof (unevolved) subgiant branch stars most probably have their origin inthe pre-enriched material rather than in internal mixing effects.Together with the age spread of the different sub-populations, ourfindings favour the formation of ω Centauri within a more massiveprogenitor.
| 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.
| uvby-β photometry of high-velocity and metal-poor stars. XI. Ages of halo and old disk stars
New uvby-β data are provided for 442 high-velocity and metal-poorstars; 90 of these stars have been observed previously by us, and 352are new. When combined with our previous two photometric catalogues, thedata base is now made up of 1533 high-velocity and metal-poor stars, allwith uvby-β photometry and complete kinematic data, such as propermotions and radial velocities taken from the literature. Hipparcos, plusa new photometric calibration for Mv also based on theHipparcos parallaxes, provide distances for nearly all of these stars;our previous photometric calibrations give values for E(b-y) and [Fe/H].The [Fe/H], V(rot) diagram allows us to separate these stars intodifferent Galactic stellar population groups, such as old-thin-disk,thick-disk, and halo. The X histogram, where X is our stellar-populationdiscriminator combining V(rot) and [Fe/H], and contour plots for the[Fe/H], V(rot) diagram both indicate two probable components to thethick disk. These population groups and Galactic components are studiedin the (b-y)0, Mv diagram, compared to theisochrones of Bergbusch & VandenBerg (2001, ApJ, 556, 322), toderive stellar ages. The two thick-disk groups have the meancharacteristics: ([Fe/H], V(rot), Age, σW') ≈ (-0.7dex, 120 km s-1, 12.5 Gyr, 62.0 km s-1), and≈(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups,-2.31 ≤ [Fe/H] ≤ -1.31, show a mean age of 13.0 ± 0.2(mean error) Gyr, giving a mean difference from the WMAP results for theage of the Universe of 0.7 ± 0.3 Gyr. These results for the agesand components of the thick disk and for the age of the Galactic halofield stars are discussed in terms of various models and ideas for theformation of galaxies and their stellar populations.
| 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.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| Analysis of medium resolution spectra by automated methods - Application to M 55 and ω Centauri
We have employed feedforward neural networks trained on syntheticspectra in the range 3800 to 5600 Å with resolutions of ~2-3Å to determine metallicities from spectra of about 1000main-sequence turn-off, subgiant and red giant stars in the globularclusters M 55 and ω Cen. The overall metallicity accuracies are ofthe order of 0.15 to 0.2 dex. In addition, we tested how well thestellar parameters log g and T_eff can be retrieved from such datawithout additional colour or photometric information. We find overalluncertainties of 0.3 to 0.4 dex for log g and 140 to 190 K for T_eff. Inorder to obtain some measure of uncertainty for the determined values of[Fe/H], log g and T_eff, we applied the bootstrap method for the firsttime to neural networks for this kind of parametrization problem. Thedistribution of metallicities for stars in ω Cen clearly shows alarge spread in agreement with the well known multiple stellarpopulations in this cluster.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| A CCD imaging search for wide metal-poor binaries
We explored the regions within a radius of 25 arcsec around 473 nearby,low-metallicity G- to M-type stars using (VR)I optical filters andsmall-aperture telescopes. About 10% of the sample was searched up toangular separations of 90 arcsec. We applied photometric and astrometrictechniques to detect true physical companions to the targets. The greatmajority of the sample stars was drawn from the Carney-Latham surveys;their metallicities range from roughly solar to [Fe/H] = -3.5 dex. OurI-band photometric survey detected objects that are between 0 and 5 magfainter (completeness) than the target stars; the maximum dynamicalrange of our exploration is 9 mag. We also investigated the literature,and inspected images from the Digitized Sky Surveys to complete oursearch. By combining photometric and proper motion measurements, weretrieved 29 previously known companions, and identified 13 new propermotion companions. Near-infrared 2MASS photometry is provided for thegreat majority of them. Low-resolution optical spectroscopy (386-1000nm) was obtained for eight of the new companion stars. Thesespectroscopic data confirm them as cool, late-type, metal-depleteddwarfs, with spectral classes from esdK7 to sdM3. After comparison withlow-metallicity evolutionary models, we estimate the masses of theproper motion companion stars to be in the range 0.5-0.1Mȯ. They are moving around their primary stars atprojected separations between 32 and 57 000 AU. These orbitalsizes are very similar to those of solar-metallicity stars of the samespectral types. Our results indicate that about 15% of the metal-poorstars have stellar companions in wide orbits, which is in agreement withthe binary fraction observed among main sequence G- to M-type stars andT Tauri stars.Based on observations made with the IAC80 telescope operated on theisland of Tenerife by the Instituto de Astrofísica de Canarias inthe Spanish Observatorio del Teide; also based on observations made withthe 2.2 m telescope of the German-Spanish Calar Alto Observatory(Almería, Spain), the William Herschel Telescope (WHT) operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos (ORM) of the Instituto deAstrofísica de Canarias; and the Telescopio Nazionale Galileo(TNG) at the ORM.The complete Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/167
| 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.
| A Search for Cool Subdwarfs: Stellar Parameters for 134 Candidates
The results of a search for cool subdwarfs are presented. Kinematic (U,V, and W) and stellar parameters (Teff, logg, [Fe/H], andξt) are derived for 134 candidate subdwarfs based onhigh-resolution spectra. The observed stars span 4200K
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries
We report 25,563 radial velocity measurements for 1359 single-linedstars in the Carney-Latham sample of 1464 stars selected for high propermotion. For 171 of these, we present spectroscopic orbital solutions. Wefind no obvious difference between the binary characteristics in thehalo and the disk populations. The observed frequency is the same, andthe period distributions are consistent with the hypothesis that the twosets of binaries were drawn from the same parent population. Thissuggests that metallicity in general, and radiative opacities inparticular, have little influence over the fragmentation process thatleads to short-period binaries. All the binaries with periods shorterthan 10 days have nearly circular orbits, while the binaries withperiods longer than 20 days exhibit a wide range of eccentricities and amedian value of 0.37. For the metal-poor high-velocity halo binaries inour sample, the transition from circular to eccentric orbits appears tooccur at about 20 days, supporting the conclusion that tidalcircularization on the main sequence is important for the oldestbinaries in the Galaxy. Some of the results presented here usedobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| Catalogue of [Fe/H] determinations for FGK stars: 2001 edition
The catalogue presented here is a compilation of published atmosphericparameters (Teff, log g, [Fe/H]) obtained from highresolution, high signal-to-noise spectroscopic observations. This newedition has changed compared to the five previous versions. It is nowrestricted to intermediate and low mass stars (F, G and K stars). Itcontains 6354 determinations of (Teff, log g, [Fe/H]) for3356 stars, including 909 stars in 79 stellar systems. The literature iscomplete between January 1980 and December 2000 and includes 378references. The catalogue is made up of two tables, one for field starsand one for stars in galactic associations, open and globular clustersand external galaxies. The catalogue is distributed through the CDSdatabase. Access to the catalogue with cross-identification to othersets of data is also possible with VizieR (Ochsenbein et al.\cite{och00}). The catalogue (Tables 1 and 2) is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/373/159 and VizieRhttp://vizier.u-strasbg.fr/.
| The galactic lithium evolution revisited
The evolution of the 7Li abundance in the Galaxy has beencomputed by means of the two-infall model of Galactic chemicalevolution. We took into account several stellar 7Li sources:novae, massive AGB stars, C-stars and Type II SNe. In particular, weadopted new theoretical yields for novae. We also took into account the7Li production from GCRs. In particular, the absolute yieldsof 7Li, as suggested by a recent reevaluation of thecontribution of GCR spallation to the 7Li abundance, havebeen adopted. We compared our theoretical predictions for the evolutionof 7Li abundance in the solar neighborhood with a newcompilation of data, where we identified the population membership ofthe stars on a kinematical basis. A critical analysis of extantobservations revealed a possible extension of the Li plateau towardshigher metallicities (up to [Fe/H] ~ -0.5 or even -0.3) with a steeprise afterwards. We conclude that 1) the 7Li contributionfrom novae is required in order to reproduce the shape of the growth ofA(Li) versus [Fe/H], 2) the contribution from Type II SNe should belowered by at least a factor of two, and 3) the 7Liproduction from GCRs is probably more important than previouslyestimated, in particular at high metallicities: by taking into accountGCR nucleosynthesis we noticeably improved the predictions on the7Li abundance in the presolar nebula and at the present timeas inferred from measures in meteorites and T Tauri stars, respectively.We also predicted a lower limit for the present time 7Liabundance expected in the bulge, a prediction which might be tested byfuture observations. Tables~3 and 4 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/Abstract.html
| Lithium abundances in metal-poor stars. I. New observations
We present the lithium measurements of a continuing programme of lightelement abundances in metal-poor stars. New equivalent widths of the Lii lambda 670.8 nm resonance line in 67 metal-poor stars covering themetallicity range -3.5 <= [Fe/H] <= -0.4 are reported. For abouthalf of this sample, the observations presented here represent the firstmeasurement of the Li i line. The sample allowed a statisticalcomparison with previous measurements from other authors and a study ofthe consistency and reliability of the quoted error bars. This papershows that for most of the stars these error bars are good estimates ofthe true uncertainties associated with the determination of theequivalent widths of the Li i line. However, about 20% of the stars withtwo or more independent measurements show discrepancies in the Li iequivalent widths; in these cases, other sources of uncertainty notproperly taken into account (binarity effects, cosmic rays, imperfectflat-field correction, continuum determination, etc.) could also beimportant. Conclusions on the possible lithium abundance trends versuseffective temperature or metallicity and on any intrinsic scatter shouldbe treated cautiously until their robustness vis-a-vis these additionaluncertainties is proved. Based on observations made with the IsaacNewton and Nordic Optical Telescopes, which are operated on the islandof La Palma by the Isaac Newton Group and the NOT ScientificAssociation, respectively, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
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