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Stellar population models in the UV. I. Characterisation of the New Generation Stellar Library
Context. The spectral predictions of stellar population models are notas accurate in the ultra-violet (UV) as in the optical wavelengthdomain. One of the reasons is the lack of high-quality stellarlibraries. The New Generation Stellar Library (NGSL), recently released,represents a significant step towards the improvement of this situation. Aims: To prepare NGSL for population synthesis, we determined theatmospheric parameters of its stars, we assessed the precision of thewavelength calibration and characterised its intrinsic resolution. Wealso measured the Galactic extinction for each of the NGSL stars. Methods: For our analyses we used ULySS, a full spectrum fittingpackage, fitting the NGSL spectra against the MILES interpolator. Results: We find that the wavelength calibration is precise up to 0.1px, after correcting a systematic effect in the optical range. Thespectral resolution varies from 3 Å in the UV to 10 Å in thenear-infrared (NIR), corresponding to a roughly constant reciprocalresolution R = ?/?? ? 1000 and an instrumentalvelocity dispersion ?ins ? 130 km s-1. Wederived the atmospheric parameters homogeneously. The precision for theFGK stars is 42 K, 0.24 and 0.09 dex for Teff, log g and[Fe/H], respectively. The corresponding mean errors are 29 K, 0.50 and0.48 dex for the M stars, and for the OBA stars they are 4.5 percent,0.44 and 0.18 dex. The comparison with the literature shows that ourresults are not biased.Table A1 is only available at 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/538/A143
| 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].
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Observational evidence for a broken Li Spite plateau and mass-dependent Li depletion
We present NLTE Li abundances for 88 stars in the metallicity range -3.5< [Fe/H] < -1.0. The effective temperatures are based on theinfrared flux method with improved E(B-V) values obtained mostly frominterstellar Na I D lines. The Li abundances were derived through MARCSmodels and high-quality UVES+VLT, HIRES+Keck and FIES+NOT spectra, andcomplemented with reliable equivalent widths from the literature. Theless-depleted stars with [Fe/H] < -2.5 and [Fe/H] > -2.5 fall intotwo well-defined plateaus of ALi = 2.18 (? = 0.04) andALi = 2.27 (? = 0.05), respectively. We show that thetwo plateaus are flat, unlike previous claims for a steep monotonicdecrease in Li abundances with decreasing metallicities. At allmetallicities we uncover a fine-structure in the Li abundances of Spiteplateau stars, which we trace to Li depletion that depends on bothmetallicity and mass. Models including atomic diffusion and turbulentmixing seem to reproduce the observed Li depletion assuming a primordialLi abundance ALi = 2.64, which agrees well with currentpredictions (ALi = 2.72) from standard Big Bangnucleosynthesis. Adopting the Kurucz overshooting model atmospheresincreases the Li abundance by +0.08 dex to ALi = 2.72, whichperfectly agrees with BBN+WMAP.Based in part on observations obtained at the W. M. Keck Observatory,the Nordic Optical Telescope on La Palma, and on data from theHIRES/Keck archive and the European Southern Observatory ESO/ST-ECFScience Archive Facility.Table 1 is only available in electronic form athttp://www.aanda.org
| 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
| The ALHAMBRA Photometric System
This paper presents the characterization of the optical range of theALHAMBRA photometric system, a 20 contiguous, equal-width, medium-bandCCD system with wavelength coverage from 3500 Å to 9700 Å.The photometric description of the system is done by presenting the fullresponse curve as a product of the filters, CCD, and atmospherictransmission curves, and using some first- and second-order moments ofthis response function. We also introduce the set of standard stars thatdefines the system, formed by 31 classic spectrophotometric standardstars which have been used in the calibration of other known photometricsystems, and 288 stars, flux calibrated homogeneously, from the NextGeneration Spectral Library (NGSL). Based on the NGSL, we determine thetransformation equations between Sloan Digital Sky Survey ugrizphotometry and the ALHAMBRA photometric system, in order to establishsome relations between both systems. Finally, we develop and discuss astrategy to calculate the photometric zero points of the differentpointings in the ALHAMBRA project.
| An absolutely calibrated Teff scale from the infrared flux method. Dwarfs and subgiants
Various effective temperature scales have been proposed over the years.Despite much work and the high internal precision usually achieved,systematic differences of order 100 K (or more) among various scales arestill present. We present an investigation based on the infrared fluxmethod aimed at assessing the source of such discrepancies and pin downtheir origin. We break the impasse among different scales by using alarge set of solar twins, stars which are spectroscopically andphotometrically identical to the Sun, to set the absolute zero point ofthe effective temperature scale to within few degrees. Our newlycalibrated, accurate and precise temperature scale applies to dwarfs andsubgiants, from super-solar metallicities to the most metal-poor starscurrently known. At solar metallicities our results validatespectroscopic effective temperature scales, whereas for [Fe/H]? -2.5our temperatures are roughly 100 K hotter than those determined frommodel fits to the Balmer lines and 200 K hotter than those obtained fromthe excitation equilibrium of Fe lines. Empirical bolometric correctionsand useful relations linking photometric indices to effectivetemperatures and angular diameters have been derived. Our results takefull advantage of the high accuracy reached in absolute calibration inrecent years and are further validated by interferometric angulardiameters and space based spectrophotometry over a wide range ofeffective temperatures and metallicities.Table 8 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A54
| Photometric Study of Kepler Asteroseismic Targets
Reported are UBV and uvby? observations of 15 candidates for Keplerprimary asteroseismic targets and 14 other stars in the Kepler field,carried out at the M.G. Fracastoro station of the Catania AstrophysicalObservatory. These data serve to plot the 29 stars in two-parameterdiagrams with the photometric indices (such as B-V or?m1) and the atmospheric parameters (such as the MKtype or [Fe/H]) as coordinates. The two-parameter diagrams show noevidence of interstellar reddening. The photometric indices B-V and? are then used to derive photometric effective temperatures,Teff(B-V) and Teff(?). ForTeff(B-V)>6400 K, the photometric effective temperaturesturn out to be systematically higher than spectroscopic effectivetemperatures by 311±34 K and 346±91 K forTeff(B-V) and Teff(?), respectively. ForTeff(B-V)<6250 K, the agreement betweenTeff(B-V) and the spectroscopic effective temperatures isvery good. The photometric surface gravities, derived from c1and ?, show a range of about a factor of two greater than theirspectroscopic counterparts do.
| Calibration of Strömgren uvby-H? photometry for late-type stars - a model atmosphere approach
Context: The use of model atmospheres for deriving stellar fundamentalparameters, such as T_eff, log g, and [Fe/H], will increase as we findand explore extreme stellar populations where empirical calibrations arenot yet available. Moreover, calibrations for upcoming large satellitemissions of new spectrophotometric indices, similar to the uvby-H?system, will be needed. Aims: We aim to test the power oftheoretical calibrations based on a new generation of MARCS models bycomparisons with observational photomteric data. Methods: Wecalculated synthetic uvby-H? colour indices from synthetic spectra.A sample of 367 field stars, as well as stars in globular clusters, isused for a direct comparison of the synthetic indices versus empiricaldata and for scrutinizing the possibilities of theoretical calibrationsfor temperature, metallicity, and gravity. Results: We show thatthe temperature sensitivity of the synthetic (b-y) colour is very closeto its empirical counterpart, whereas the temperature scale based uponH? shows a slight offset. The theoretical metallicity sensitivityof the m1 index (and for G-type stars its combination withc_1) is somewhat higher than the empirical one, based upon spectroscopicdeterminations. The gravity sensitivity of the synthetic c1index shows satisfactory behaviour when compared to obervations of Fstars. For stars cooler than the sun, a deviation is significant in thec1-(b-y) diagram. The theoretical calibrations of (b-y),(v-y), and c1 seem to work well for Pop II stars and lead toeffective temperatures for globular cluster stars supporting recentclaims that atomic diffusion occurs in stars near the turnoff point ofNGC 6397. Conclusions: Synthetic colours of stellar atmospherescan indeed be used, in many cases, to derive reliable fundamentalstellar parameters. The deviations seen when compared to observationaldata could be due to incomplete linelists but are possibly also due tothe effects of assuming plane-parallell or spherical geometry and LTE.Model colours are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/498/527
| Automated classification of ELODIE stellar spectral library using probabilistic artificial neural networks
A Probabilistic Neural Network model has been used for automatedclassification of ELODIE stellar spectral library consisting of about2000 spectra into 158 known spectro-luminosity classes. The full spectrawith 561 flux bins and a PCA reduced set of 57, 26 and 16 componentshave been used for the training and test sessions. The results show aspectral type classification accuracy of 3.2 sub-spectral type andluminosity class accuracy of 2.7 for the full spectra and an accuracy of3.1 and 2.6 respectively with the PCA set. This technique will be usefulfor future upcoming large databases and their rapid classification.
| Kepler primary asteroseismic targets - ground-based study .
Reported are results of ground-based spectroscopic and photometricobservations of Kepler primary asteroseismic targets. We determine log T_eff, log g, [Fe/H], vsin i and the mean radial velocity, v_r, forall these stars. For new spectroscopic binaries, we provide orbitalsolutions. Finally, we compute evolutionary models using Monte Carlosimulations.
| Spectroscopic Study of Kepler Asteroseismic Targets
Reported are spectroscopic observations of 15 candidates for Keplerprimary asteroseismic targets and 14 other stars in the Kepler field,carried out at three observatories. For all these stars, the radialvelocities, effective temperature, surface gravity, metallicity, and theprojected rotational velocity are derived from two separate sets of databy means of two independent methods. In addition, MK type is estimatedfrom one of these sets of data.Three stars, HIP94335, HIP94734, and HIP94743, are found to havevariable radial-velocity. For HIP94335 = FLLyr, a well-known Algol-typeeclipsing variable and a double-lined spectroscopic binary, the orbitalelements computed from our data agree closely with those of Popper etal. For HIP94734 and HIP94743 = V2077 Cyg, which we discover to besingle-lined systems, orbital elements are derived. In addition, fromour value of the orbital period and the Hipparcos epoch photometry,HIP94743 is demonstrated to be a detached eclipsing binary.
| Speckle interferometry of metal-poor stars in the solar neighborhood. I
We report the results of speckle-interferometric observations of 109high proper-motion metalpoor stars made with the 6-m telescope of theSpecial Astrophysical Observatory of the Russian Academy of Sciences. Weresolve eight objects—G102-20, G191-55, BD+19° 1185A, G89-14,G87-45, G87-47, G111-38, and G114-25—into individual componentsand we are the first to astrometrically resolve seven of these stars.New resolved systems included two triple (G111-38, G87-47) and onequadruple (G89-14) star. The ratio ofsingle-to-binary-to-triple-to-quadruple systems among the stars of oursample is equal to 71:28:6:1.
| Measuring the Balmer Jump and the Effective Gravity in FGK Stars
It is difficult to accurately measure the effective gravity (logg) inlate-type stars using broadband (e.g., UBV or SDSS) or intermediate-band(uvby) photometric systems, especially when the stars can cover a rangeof metallicities and reddenings. However, simple spectroscopicobservational and data reduction techniques can yield accurate valuesfor logg through comparison of the Balmer jumps of low-resolutionspectra with recent grids of synthetic flux spectra.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Metallicity and absolute magnitude calibrations for UBV photometry
Calibrations are presented here for metallicity ([Fe/H]) in terms of theultraviolet excess, [δ(U - B) at B - V = 0.6, hereafterδ0.6], and also for the absolute visual magnitude(MV) and its difference with respect to the Hyades(ΔMHV) in terms of δ0.6 and(B - V), making use of high-resolution spectroscopic abundances from theliterature and Hipparcos parallaxes. The relation[Fe/H]-δ0.6 has been derived for dwarf plus turn-offstars, and also for dwarf, turn-off, plus subgiant stars classifiedusing the MV-(B - V)0 plane of Fig. 11, which iscalibrated with isochrones from Bergbusch & VandenBerg (and alsoVandenBerg & Clem). The [Fe/H]-δ0.6 relations inour equations (5) and (6) agree well with those of Carney, as can beseen from Fig. 5(a). Within the uncertainties, the zero-points,+0.13(+/-0.05) of equation (5) and +0.13(+/-0.04) of equation (6), arein good agreement with the photometric ones of Cameron and of Carney,and close to the spectroscopic ones of Cayrel et al. and of Boesgaard& Friel for the Hyades open cluster. Good quantitative agreementbetween our estimated [Fe/H] abundances with those from uvby-βphotometry and spectroscopic [Fe/H]spec values demonstratesthat our equation (6) can be used in deriving quality photometric metalabundances for field stars and clusters using UBV data from variousphotometric surveys.For dwarf and turn-off stars, a new hybrid MV calibration ispresented, based on Hipparcos parallaxes withσπ/π <= 0.1 and with a dispersion of +/-0.24in MV. This hybrid MV calibration containsδ0.6 and (B - V) terms, plus higher order cross-termsof these, and is valid for the ranges of +0.37 <= (B - V)0<= +0.88,- 0.10 <= δ0.6 <= +0.29 and 3.44<= MV <= 7.23. For dwarf and turn-off stars, therelation for ΔMHV is revised and updated interms of (B - V) and δ0.6, for the ranges of -0.10<= δ0.6 <= +0.29, and +0.49 <= (B -V)0 <= +0.89, again making use of Hipparcos parallaxeswith σπ/π <= 0.1. These parallaxes formetal-poor dwarf and turn-off stars in our sample reveal that thedifference of ΔMHV(B - V) relative to Hyadesat (B - V) = +0.70 should be 1.37mag, instead of the 1.58mag given byLaird et al. In general, Hipparcos parallaxes are larger thanground-based ones, causing a divergence of ourΔMHV(B - V,δ0.6) relation(the solid line in Fig. 15b), from the one of Laird et al. (the dashedline) for the range +0.10 <= δ0.6 <= +0.29 ourabsolute magnitudes are fainter, as has been confirmed for localsubdwarfs by Reid. Our final calibrations forΔMHV(B - V, δ0.6),equations (16) and (17), are third-order polynomials inδ0.6, pass through the origin, and provide photometricdistances in reasonable agreement with those obtained directly fromHipparcos parallaxes (Fig. 18).
| 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.
| Chemical abundances of very metal-poor stars
High-resolution and high signal-to-noise ratio spectra of 32 verymetal-poor stars were obtained with the Coudé echellespectrograph mounted on the 2.16-m telescope at the NationalAstronomical Observatories (Xinglong, China). Equivalent widths of FeI,FeII, OI, NaI, MgI, AlI, SiI, SiII, KI, CaI, ScII, TiI, VI, CrI, MnI,NiI, CuI and BaII lines were measured. Stellar effective temperatureswere determined by colour indices. Stellar surface gravities werecalculated from Hipparcos parallaxes and stellar evolutionary tracks.Photospheric abundances of 16 elements were derived by localthermodynamical equilibrium analysis. Stellar space motions (U, V, W)and Galactic orbital parameters were calculated. Based on kinematics,sample stars were separated into dissipative collapse and accretioncomponents of halo population. The global kinematics of the twocomponents were analysed. Element abundances were discussed as functionsof metallicities. The results of oxygen and α-elements abundanceconfirmed the previous works. The [K/Fe] shows a gradual systematicincrease toward a lower metallicity, such as in the case ofα-elements. The [Ba/Fe] trend suggests that the s-processdominated Ba production at least for the metal-poor stars with[Fe/H]> -2.0.
| 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.
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| 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
| Lithium Abundance of Metal-poor Stars
High-resolution, high signal-to-noise ratio spectra have been obtainedfor 32 metal-poor stars. The equivalent widths of Li λ6708Åwere measured and the lithium abundances were derived. The averagelithium abundance of 21 stars on the lithium plateau is 2.33±0.02dex. The Lithium plateau exhibits a marginal trend along metallicity,dA(Li)/d[Fe/H] = 0.12±0.06, and no clear trend with the effectivetemperature. The trend indicates that the abundance of lithium plateaumay not be primordial and that a part of the lithium was produced inGalactic Chemical Evolution (GCE).
| Abundances for metal-poor stars with accurate parallaxes. I. Basic data
We present element-to-element abundance ratios measured from highdispersion spectra for 150 field subdwarfs and early subgiants withaccurate Hipparcos parallaxes (errors <20%). For 50 stars new spectrawere obtained with the UVES on Kueyen (VLT UT2), the McDonald 2.7 mtelescope, and SARG at TNG. Additionally, literature equivalent widthswere taken from the works by Nissen & Schuster, Fulbright, andProchaska et al. to complement our data. The whole sample includes boththick disk and halo stars (and a few thin disk stars); most stars havemetallicities in the range -2<[Fe/H]<-0.6. We found our data, thatof Nissen & Schuster, and that of Prochaska to be of comparablequality; results from Fulbright scatter a bit more, but they are stillof very good quality and are extremely useful due to the large size ofhis sample. The results of the present analysis will be used inforthcoming papers to discuss the chemical properties of thedissipational collapse and accretion components of our Galaxy.Based in part on data collected at the European Southern Observatory,Chile, at the MacDonald Observatory, Texas, USA, and at the TelescopioNazionale Galileo, Canary Island, INAF,Italy-Spain.}\fnmsep\thanks{Table 1 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia\resizebox{8.8cm}{2.2mm}htpp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/187}
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Abundances of Cu and Zn in metal-poor stars: Clues for Galaxy evolution
We present new observations of copper and zinc abundances in 90metal-poor stars, belonging to the metallicity range -3<[Fe/H]<-0.5. The present study is based on high resolutionspectroscopic measurements collected at the Haute Provence Observatoire(R= 42 000, S/N>100). The trend of Cu and Zn abundances as a functionof the metallicity [Fe/H] is discussed and compared to that of otherheavy elements beyond iron. We also estimate spatial velocities andgalactic orbital parameters for our target stars in order to disentanglethe population of disk stars from that of halo stars using kinematiccriteria. In the absence of a firm a priori knowledge of thenucleosynthesis mechanisms controlling Cu and Zn production, and of therelative stellar sites, we derive constraints on these last from thetrend of the observed ratios [Cu/Fe] and [Zn/Fe] throughout the historyof the Galaxy, as well as from a few well established properties ofbasic nucleosynthesis processes in stars. We thus confirm that theproduction of Cu and Zn requires a number of different sources (neutroncaptures in massive stars, s-processing in low and intermediate massstars, explosive nucleosynthesis in various supernova types). We alsoattempt a ranking of the relative roles played by different productionmechanisms, and verify these hints through a simple estimate of thegalactic enrichment in Cu and Zn. In agreement with suggestionspresented earlier, we find evidence that type Ia Supernovae must play arelevant role, especially for the production of Cu. Based on the spectracollected with the 1.93-m telescope of Haute Provence Observatory.
| 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.
| 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.
| A search for previously unrecognized metal-poor subdwarfs in the Hipparcos astrometric catalogue
We have identified 317 stars included in the Hipparcos astrometriccatalogue that have parallaxes measured to a precision of better than 15per cent, and the location of which in the(MV,(B-V)T) diagram implies a metallicitycomparable to or less than that of the intermediate-abundance globularcluster M5. We have undertaken an extensive literature search to locateStrömgren, Johnson/Cousins and Walraven photometry for over 120stars. In addition, we present new UBV(RI)C photometry of 201of these candidate halo stars, together with similar data for a further14 known metal-poor subdwarfs. These observations provide the firstextensive data set of RCIC photometry ofmetal-poor, main-sequence stars with well-determined trigonometricparallaxes. Finally, we have obtained intermediate-resolution opticalspectroscopy of 175 stars. 47 stars still lack sufficient supplementaryobservations for population classification; however, we are able toestimate abundances for 270 stars, or over 80 per cent of the sample.The overwhelming majority have near-solar abundance, with theirinclusion in the present sample stemming from errors in the colourslisted in the Hipparcos catalogue. Only 44 stars show consistentevidence of abundances below [Fe/H]=-1.0. Nine are additions to thesmall sample of metal-poor subdwarfs with accurate photometry. Weconsider briefly the implication of these results for clustermain-sequence fitting.
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לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h09m01.41s |
| סירוב: | +42°51'54.9" |
| גודל גלוי: | 10.136 |
| תנועה נכונה: | 118.3 |
| תנועה נכונה: | 340.3 |
| B-T magnitude: | 10.704 |
| V-T magnitude: | 10.183 |
קטלוגים וכינוים:
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