Contents
Images
Upload your image
DSS Images Other Images
Related articles
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
| The atmospheric parameters and spectral interpolator for the MILES stars
Context. Empirical libraries of stellar spectra are used to classifystars and synthetize stellar populations. MILES is a mediumspectral-resolution library in the optical domain covering a wide rangeof temperatures, surface gravities and metallicities. Aims: Weredetermine the atmospheric parameters of these stars in order toimprove the homogeneity and accuracy. We build an interpolating functionthat returns a spectrum as a function of the three atmosphericparameters, and finally we characterize the precision of the wavelengthcalibration and stability of the spectral resolution. Methods: Weused the ULySS program with the ELODIE library as a reference andcompared the results with those in the literature. Results: Weobtain precisions of 60 K, 0.13, and 0.05 dex, respectively, forTeff, log g, and [Fe/H] for the FGK stars. For the M stars,the mean errors are 38 K, 0.26, and 0.12 dex and 3.5%, 0.17, and 0.13dex for the OBA. We construct an interpolator that we test against theMILES stars themselves. We test it also by measuring the atmosphericparameters of the CFLIB stars with MILES as reference and find it to bemore reliable than the ELODIE interpolator for the evolved hot stars,like those of the blue horizontal branch in particular.FITS files are only and Table 1 also available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A165
| Element abundances in the stars of the MILES spectral library: the Mg/Fe ratio
We have obtained [Mg/Fe] measurements for 76.3 per cent of the stars inthe Mid-resolution Isaac Newton Telescope Library of Empirical Spectra(MILES) spectral library used for understanding stellar atmospheres andstellar populations in galaxies and star clusters. These abundanceratios were obtained through (1) a compilation of values from theliterature using abundances from high-resolution (HR) spectroscopicstudies and (2) a robust spectroscopic analysis using the MILESmid-resolution (MR) optical spectra. All the [Mg/Fe] values werecarefully calibrated to a single uniform scale, by using an extensivecontrol sample with results from HR spectra. The small averageuncertainties in the calibrated [Mg/Fe] values [respectively 0.09 and0.12 dex with methods (1) and (2)] and the good coverage of the starswith [Mg/Fe] over stellar atmospheric parameter space of the librarywill permit the building of new simple stellar populations (SSPs) withempirical ?-enhancements. These will be available for a range of[Mg/Fe], including both sub-solar and super-solar values, and forseveral metallicities and ages. These models will open up new prospectsfor testing and applications of evolutionary stellar populationsynthesis.
| Coudé-feed stellar spectral library - atmospheric parameters
Context. Empirical libraries of stellar spectra play an important rolein different fields. For example, they are used as reference for theautomatic determination of atmospheric parameters, or for buildingsynthetic stellar populations to study galaxies. The CFLIB(Coudé-feed library, Indo-US) database is at present one of themost complete libraries, in terms of its coverage of the atmosphericparameters space (T{eff}, log g and [Fe/H]) and wavelengthcoverage 3460-9464 Å at a resolution of 1 Å FWHM. Althoughthe atmospheric parameters of most of the stars were determined fromdetailed analyses of high-resolution spectra, for nearly 300 of the 1273stars of the library at least one of the three parameters is missing.For the others, the measurements, compiled from the literature, areinhomogeneous. Aims: In this paper, we re-determine theatmospheric parameters, directly using the CFLIB spectra, and comparethem to the previous studies. Methods: We use the ULySS programto derive the atmospheric parameters, using the ELODIE library as areference. Results: Based on comparisons with several previousstudies we conclude that our determinations are unbiased. For the 958 F,G, and K type stars the precision on T{eff}, log g, and[Fe/H] is respectively 43 K, 0.13 dex and 0.05 dex. For the 53 M starsthey are 82 K, 0.22 dex and 0.28 dex. And for the 260 OBA type stars therelative precision on T{eff} is 5.1%, and on log g, and[Fe/H] the precision is respectively 0.19 dex and 0.16 dex. Theseparameters will be used to re-calibrate the CFLIB fluxes and to producesynthetic spectra of stellar populations.Tables 2 and 3 are only available in electronic form 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/525/A71
| Multiplicity and Period Distribution of Population II Field Stars in Solar Vicinity
We examine a sample of 223 F, G, and early K metal-poor subdwarfs ([m/H]< -1) with high proper motions (?>0farcs2yr-1) at distances of up to 250 pc from the Sun. Bymeans of our own speckle interferometric observations conducted on the 6m Bolshoi Azimuthal Telescope of the Special Astrophysical Observatoryof the Russian Academy of Sciences, and the spectroscopic and visualdata taken from the literature, we determine the frequency of binary andmultiple systems in this sample. The ratio of single, binary, triple,and quadruple systems among 221 primary components of the sample is147:64:9:1. We show that the distribution of orbital periods of binaryand multiple subdwarfs is asymmetric in the range of up to P =1010 days, and has a maximum at P =102-103 days, which differs from the distribution,obtained for the thin disk G dwarfs. We estimated the number ofundetected companions in our sample. Comparing the frequency of binarysubdwarfs in the field and in the globular clusters, we show that theprocess of halo field star formation by the means of destruction ofglobular clusters is very unlikely in our Galaxy. We discuss themultiplicity of old metal-poor stars in nearby stellar streams.
| The Lick/SDSS Library. I. Synthetic Index Definition and Calibration
A new synthetic library of spectral feature indices, Lick/Sloan DigitalSky Survey (SDSS), for stellar population studies is presented.Lick/SDSS is computed from synthetic spectra with resolving power R =1800 to fully exploit the content of the spectroscopic SDSS-DR7 stellardatabase. The Lick/SDSS system is based on the Lick/IDS one complementedwith a UV index in the wavelength region of Ca II H and K lines. Thesystem is well suited to study ?-element abundances in F, G, and Kstars. The reliability of synthetic indices in reproducing the behaviorsof observational ones with effective temperature, surface gravity,overall metallicity, and ?-element abundances is tested by usingempirical stellar libraries (ELODIE, INDO-U.S., and MILES) and theSDSS-DR7 spectroscopic database. The importance of using the sametemperature scale in comparing theoretical and observational indices isdiscussed. The full consistency between Lick/SDSS and observationalindices derived from the above mentioned stellar libraries is assessed.The comparison with indices computed from SDSS-DR7 spectra evidencesgood consistency for "dwarf" stars and significant disagreement for"giant" stars due to systematic overestimation of the stellar Teff by the SEGUE Stellar Parameter Pipeline.
| 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.
| 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.
| 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.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| 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.
| Metal-poor Field Blue Stragglers: More Evidence for Mass Transfer
We report radial velocity studies of five candidate metal-poor fieldblue stragglers, all known to be deficient in lithium. Four of the fivestars are single-lined spectroscopic binaries, with periods ranging from302 to 840 days, and low orbital eccentricities, in agreement withsimilar behavior found for other blue straggler candidates by Preston& Sneden and Carney et al. The limited data available for lithiumabundances indicate that all blue straggler binaries have depletedlithium, but that constant velocity stars generally have normal lithiumabundances. This suggests that the ``lithium gap'' for hot metal-poormain-sequence stars may not exist or lies at higher temperatures thanfound in the Hyades. Our results and those of Preston & Sneden showhigher values of vrotsini for the binary stars than those ofcomparable temperature constant velocity stars. The orbital periods aretoo long for tidal effects to be important, implying that spin-up duringmass transfer when the orbital separations and periods were smaller isthe cause of the enhanced rotation. The mass function distribution issteeper for the blue straggler binary stars than that of lower masssingle-lined spectroscopic binaries, indicating a narrower range insecondary masses. We argue that if all secondaries are white dwarfs withthe same mass, it is probably around 0.55 Msolar. The modelsof Rappaport et al., applied to white dwarf secondaries, suggest thatthe orbital elements of all metal-poor binary blue stragglers areconsistent with stable mass transfer, with the possible exception ofG202-65.Some of the results presented here used observations made with theMultiple Mirror Telescope, a joint facility of the SmithsonianInstitution and the University of Arizona.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
In order to investigate the formation of O I 7771-5 and [O I] 6300/6363lines, extensive non-LTE calculations for neutral atomic oxygen werecarried out for wide ranges of model atmosphere parameters, which areapplicable to early-K through late-F halo/disk stars of variousevolutionary stages.The formation of the triplet O I lines was found to be well described bythe classical two-level-atom scattering model, and the non-LTEcorrection is practically determined by the parameters of theline-transition itself without any significant relevance to the detailsof the oxygen atomic model. This simplifies the problem in the sensethat the non-LTE abundance correction is essentially determined only bythe line-strength (Wlambda ), if the atmospheric parametersof Teff, log g, and xi are given, without any explicitdependence of the metallicity; thus allowing a useful analytical formulawith tabulated numerical coefficients. On the other hand, ourcalculations lead to the robust conclusion that LTE is totally valid forthe forbidden [O I] lines.An extensive reanalysis of published equivalent-width data of O I 7771-5and [O I] 6300/6363 taken from various literature resulted in theconclusion that, while a reasonable consistency of O I and [O I]abundances was observed for disk stars (-1 <~ [Fe/H] <~ 0), theexistence of a systematic abundance discrepancy was confirmed between OI and [O I] lines in conspicuously metal-poor halo stars (-3 <~[Fe/H] <~ -1) without being removed by our non-LTE corrections, i.e.,the former being larger by ~ 0.3 dex at -3 <~ [Fe/H] <~ -2.An inspection of the parameter-dependence of this discordance indicatesthat the extent of the discrepancy tends to be comparatively lessenedfor higher Teff/log g stars, suggesting the preference ofdwarf (or subgiant) stars for studying the oxygen abundances ofmetal-poor stars.Tables 2, 5, and 7 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/402/343 and Table\ref{tab3} is only available in electronic form athttp://www.edpsciences.org
| IRFM temperature calibrations for the Vilnius, Geneva, RI(C) and DDO photometric systems
We have used the infrared flux method (IRFM) temperatures of a largesample of late type dwarfs given by Alonso et al. (\cite{alonso:irfm})to calibrate empirically the relations Teff=f (colour,[Fe/H]) for the Vilnius, Geneva, RI(C) (Cousins) and DDOphotometric systems. The resulting temperature scale and intrinsiccolour-colour diagrams for these systems are also obtained. From thisscale, the solar colours are derived and compared with those of thesolar twin 18 Sco. Since our work is based on the same Teffand [Fe/H] values used by Alonso et al. (\cite{alonso:escala}) tocalibrate other colours, we now have an homogeneous calibration for alarge set of photometric systems.Based on data from the GCPD.
| 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. XIV. Spectroscopic Binaries among Metal-poor Field Blue Stragglers
We summarize the results from a program of monitoring the radialvelocities of 10 metal-poor, high-velocity field stars whose colors are0.01 to 0.13 mag bluer than main-sequence turnoffs ofcomparable-metallicity globular clusters. Two of the candidate halo bluestragglers (BD +72 94 and BD +40 1166) show no signs of velocityvariability, one (HD 84937) shows only weak signs of variability, one(BD +25 1981) appears to be a very long-period binary, and six (BD -122669, HD 97916, HD 106516, BD +51 1817, G66-30, and G202-65) aresingle-lined spectroscopic binaries, with periods ranging from 167 to844 days. Velocity coverage for the four candidates without orbitalsolutions ranges from 15.9 to 19.0 years. The orbital eccentricities areall low, e<0.30 and =0.11. Five of the six binary orbitshave very low eccentricities, with =0.07. We have reanalyzedthe velocity data from Preston & Sneden and have derived orbitalsolutions similar to theirs for 10 of the spectroscopic binaries amongtheir ``blue metal-poor'' stars with [Fe/H]<=-0.6. We confirm theirconclusion that the binary frequency is high; we find 47+/-10% if weinclude only the definite binaries with [Fe/H]<=-0.6. Our orbitalsolutions for the seven binaries with periods longer than 20 days allhave low eccentricities, with e<=0.26 and =0.11. Theseorbital characteristics are very similar to the Ba II, CH, subgiant CH,and dwarf carbon stars, suggesting that mass transfer has been involvedin their formation. Of the five binary stars in our program withpublished abundances of lithium, all have been found to be deficient(and one in beryllium as well). In contrast, two of the three apparentlysingle stars have published lithium abundances and show no deficiency.The mass functions for the six binaries in our program and seven similarsystems studied by Preston & Sneden are consistent with their unseencompanions all being white dwarfs with M~0.55 Msolar andrandom orbital inclinations. Taking all of our observations and those ofothers together, we argue that the results are consistent with all fieldblue stragglers being binary systems with long periods and loweccentricities, the primary stars being deficient in lithium and thesecondary stars being normal-mass white dwarfs. All these properties aresuggestive of a blue-straggler formation model that involves masstransfer. For six of the 13 stars in the two programs for whichs-process elemental abundances are available, no signs of enhancementare discernible, suggesting that the donor star was a first-ascent redgiant. For the star with the longest orbital period (1307 days), CS22956-028, s-process abundance enhancements have been reported. Thisstar may be a precursor to the subgiant CH class, as suggested by Luck& Bond. Some of the results presented here used observations madewith the Multiple Mirror Telescope, a joint facility of the SmithsonianInstitution 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/.
| A database of high and medium-resolution stellar spectra
We present a database of 908 spectra of 709 stars obtained with theELODIE spectrograph at the Observatoire de Haute-Provence. 52 orders ofthe echelle spectra have been carefully fitted together to providecontinuous, high-resolution spectra in the wavelength range lambdalambda = 410-680 nm. The archive provides a large coverage of the spaceof atmospheric parameters: T_eff from 3700 K to 13 600 K, log g from0.03 to 5.86 and [Fe/H] from -2.8 to +0.7. At the nominal resolution,R=42 000, the mean signal-to-noise ratio is 150 per pixel. The spectragiven at this resolution are normalized to their pseudo-continuum andare intended to serve for abundance studies, spectral classification andtests of stellar atmosphere models. A lower resolution version of thearchive, at R=10 000, is calibrated in physical flux with a broad-bandphotometric precision of 2.5% and narrow-band precision of 0.5%. It iswell suited to stellar population synthesis of galaxies and clusters,and to kinematical investigations of stellar systems. The archive isdistributed in FITS format through the HYPERCAT and CDS databases. Basedon observations made on the 193 cm telescope at the Haute-ProvenceObservatory, France. Table 1 is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/1048
| Abundances and Evolution of Lithium in the Galactic Halo and Disk
We have measured the Li abundance of 18 stars with -2<~[Fe/H]<~-1and 6000<~Teff<~6400 K, a parameter range that waspoorly represented in previous studies. We examine the Galactic chemicalevolution (GCE) of this element, combining these data with previoussamples of turnoff stars over the full range of halo metallicities. Wefind that A(Li) increases from a level of ~2.10 at [Fe/H]=-3.5 to ~2.40at [Fe/H]=-1.0, where A(Li)=log10(n(Li)/n(H))+12.00. We comparethe observations with several GCE calculations, including existingone-zone models and a new model developed in the framework ofinhomogeneous evolution of the Galactic halo. We show that Li evolved ata constant rate relative to iron throughout the halo and old disk epochsbut that during the formation of young disk stars, the production of Lirelative to iron increased significantly. These observations can beunderstood in the context of models in which postprimordial Li evolutionduring the halo and old disk epochs is dominated by Galactic cosmic-rayfusion and spallation reactions, with some contribution from theν-process in supernovae. The onset of more efficient Li production(relative to iron) in the young disk coincides with the appearance of Lifrom novae and asymptotic giant branch (AGB) stars. The major challengefacing the models is to reconcile the mild evolution of Li during thehalo and old disk phases with the more efficient production (relative toiron) at [Fe/H]>-0.5. We speculate that cool-bottom processing(production) of Li in low-mass stars may provide an importantlate-appearing source of Li, without attendant Fe production, that mightexplain the Li production in the young disk. Based on observationsobtained with the University College London échelle spectrograph(UCLES) on the Anglo-Australian Telescope (AAT) and the Utrechtéchelle spectrograph (UES) on the William Herschel Telescope(WHT).
| Ultra-Lithium-deficient Halo Stars and Blue Stragglers: A Common Origin?
We present data for four ultra-Li-deficient, warm, halo stars. The Lideficiency of two of these is a new discovery. Three of the four starshave effective temperatures Teff~6300 K, in contrast topreviously known Li-deficient halo stars, which spanned the temperaturerange of the Spite plateau. In this paper we propose that these andpreviously known ultra-Li-deficient halo stars may have had theirsurface lithium abundances reduced by the same mechanism as produceshalo field blue stragglers. Even though these stars have yet to revealthemselves as blue stragglers, they might be regarded as``blue-stragglers-to-be.'' In our proposed scenario, the surfaceabundance of Li in these stars could be destroyed (1) during the normalpre-main-sequence single-star evolution of their low-mass precursors,(2) during the post-main-sequence evolution of an evolved mass donor,and/or (3) via mixing during a mass-transfer event or stellar merger.The warmest Li-deficient stars at the turnoff would be regarded asemerging ``canonical'' blue stragglers, whereas cooler ones representsub-turnoff-mass blue-stragglers-to-be. The latter are presently hiddenon the main sequence, Li depletion being possibly the clearest signatureof their past history and future significance. Eventually, themain-sequence turnoff will reach down to their mass, exposing thoseLi-depleted stars as canonical blue stragglers when normal stars of thatmass evolve away. Arguing against this unified view is the observationthat the three Li-depleted stars at Teff~=6300 K are allbinaries, whereas very few of the cooler systems show evidence forbinarity; it is thus possible that two separate mechanisms areresponsible for the production of Li-deficient main-sequence halo stars.Based on observations obtained with the University College Londonéchelle spectrograph (UCLES) on the Anglo-Australian Telescope(AAT) and the Utrecht échelle spectrograph (UES) on the WilliamHerschel Telescope (WHT).
| Abundances of light elements in metal-poor stars. III. Data analysis and results
We present the results of the analysis of an extensive set of new andliterature high quality data concerning Fe, C, N, O, Na, and Mg. Thisanalysis exploited the T_eff scale determined in Gratton et al. (1996a),and the non-LTE abundance corrections computed in Gratton et al.(1999a). Results obtained with various abundance indices are discussedand compared. Detailed comparison with models of galactic chemicalevolution will be presented in future papers of this series. Our non-LTEanalysis yields the same O abundances from both permitted and forbiddenlines for stars with T_eff >4600 K, in agreement with King (1993),but not with other studies using a lower T_eff -scale for subdwarfs.However, we obtain slightly smaller O abundances for the most luminousmetal-poor field stars than for fainter stars of similar metallicities,an effect attributed to inadequacies of the adopted model atmospheres(Kurucz 1992, with overshooting) for cool stars. We find a nearlyconstant O overundance in metal-poor stars ([Fe/H]<-0.8), at a meanvalue of 0.46+/- 0.02 dex (sigma =0.12, 32 stars), with only a gentleslope with [Fe/H] ( ~ -0.1); this result is different from the steeperslope recently obtained using OH band in the near UV. If only bonafideunmixed stars are considered, C abundances scale with Fe ones (i.e.[C/Fe]~ 0) down to [Fe/H] ~ -2.5. Due to our adoption of a differentT_eff scale, we do not confirm the slight C excess in the most metalpoor disk dwarfs (-0.8<[Fe/H]<-0.4) found in previousinvestigations. Na abundances scale as Fe ones in the high metallicityregime, while metal-poor stars present a Na underabundance. None of thefield stars analyzed belong to the group of O-poor and Na-rich starsobserved in globular clusters. Na is deficient with respect to Mg inhalo and thick disk stars; within these populations, Na deficiency maybe a slow function of [Mg/H]. Solar [Na/Mg] ratios are obtained for thindisk stars. Tables~ 2 to 9 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strabg.fr/Abstract.html
| 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
| The evolution of ^6Li in standard cosmic-ray nucleosynthesis
We review the Galactic chemical evolution of ^6Li and compare theseresults with recent observational determinations of the lithium isotopicratio. In particular, we concentrate on so-called standard Galacticcosmic-ray nucleosynthesis in which Li, Be, and B are produced(predominantly) by the inelastic scattering of accelerated protons andalpha off of CNO nuclei in the ambient interstellar medium. If O/Fe isconstant at low metallicities, then the ^6Li versus Fe/H evolution - aswell as Be and B versus Fe/H - has difficulty in matching theobservations. However, recent determinations of Population II oxygenabundances, as measured via OH lines, indicate that O/Fe increases atlower metallicity; if this trend is confirmed, then the ^6Li evolutionin a standard model of cosmic-ray nucleosynthesis is consistent with thedata. We also show that another key indicator of ^6LiBeB origin is the^6Li/Be ratio which also fits the available data if O/Fe is not constantat low metallicity. Finally we note that ^6Li evolution in this scenariocan strongly constrain the degree to which ^6Li and ^7Li are depleted inhalo stars.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cassiopeia |
| Right ascension: | 01h47m12.39s |
| Declination: | +73°28'27.2" |
| Apparent magnitude: | 9.98 |
| Proper motion RA: | -204 |
| Proper motion Dec: | 161.1 |
| B-T magnitude: | 10.426 |
| V-T magnitude: | 10.017 |
Catalogs and designations:
|
