Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Chemical similarities between Galactic bulge and local thick disk red giant stars
Context: The evolution of the Milky Way bulge and its relationship withthe other Galactic populations is still poorly understood. The bulge hasbeen suggested to be either a merger-driven classical bulge or theproduct of a dynamical instability of the inner disk. Aims: To probethe star formation history, the initial mass function and stellarnucleosynthesis of the bulge, we performed an elemental abundanceanalysis of bulge red giant stars. We also completed an identical studyof local thin disk, thick disk and halo giants to establish the chemicaldifferences and similarities between the various populations. Methods:High-resolution infrared spectra of 19 bulge giants and 49 comparisongiants in the solar neighborhood were acquired with Gemini/Phoenix. Allstars have similar stellar parameters but cover a broad range inmetallicity. A standard 1D local thermodynamic equilibrium analysisyielded the abundances of C, N, O and Fe. A homogeneous and differentialanalysis of the bulge, halo, thin disk and thick disk stars ensured thatsystematic errors were minimized. Results: We confirm thewell-established differences for [O/Fe] (at a given metallicity) betweenthe local thin and thick disks. For the elements investigated, we findno chemical distinction between the bulge and the local thick disk,which is in contrast to previous studies relying on literature valuesfor disk dwarf stars in the solar neighborhood. Conclusions: Ourfindings suggest that the bulge and local thick disk experiencedsimilar, but not necessarily shared, chemical evolution histories. Weargue that their formation timescales, star formation rates and initialmass functions were similar.
| Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants
We present the parameters of 891 stars, mostly clump giants, includingatmospheric parameters, distances, absolute magnitudes, spatialvelocities, galactic orbits and ages. One part of this sample consistsof local giants, within 100 pc, with atmospheric parameters eitherestimated from our spectroscopic observations at high resolution andhigh signal-to-noise ratio, or retrieved from the literature. The otherpart of the sample includes 523 distant stars, spanning distances up to1 kpc in the direction of the North Galactic Pole, for which we haveestimated atmospheric parameters from high resolution but lowsignal-to-noise Echelle spectra. This new sample is kinematicallyunbiased, with well-defined boundaries in magnitude and colours. Werevisit the basic properties of the Galactic thin disk as traced byclump giants. We find the metallicity distribution to be different fromthat of dwarfs, with fewer metal-rich stars. We find evidence for avertical metallicity gradient of -0.31 dex kpc-1 and for atransition at ~4-5 Gyr in both the metallicity and velocities. Theage-metallicity relation (AMR), which exhibits a very low dispersion,increases smoothly from 10 to 4 Gyr, with a steeper increase for youngerstars. The age-velocity relation (AVR) is characterized by thesaturation of the V and W dispersions at 5 Gyr, and continuous heatingin U.
| Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity
We present rotational and radial velocities for a sample of 761 giantsselected from the Hipparcos Catalogue to lie within 100 pc of the Sun.Our original goal was to examine stellar rotation in field giants usingspectroscopic line broadening to look for evidence of excess rotationthat could be attributed to planets that were engulfed as the parentstars expanded. Thus we were obliged to investigate other sources ofline broadening, including tidal coupling in close binaries andmacroturbulence. For all the binaries in our sample with periods shorterthan 20 days the orbits have been circularized, while about half theorbits with periods in the range 20-100 days still show significanteccentricity. All our primaries in orbits shorter than 30 days show linebroadening consistent with synchronized rotation, while about half theprimaries with periods in the range 30-120 days are synchronized. Tostudy the dependence of rotation on stellar evolution when tidal effectsare not important, we used a subsample of single stars and members inwide binaries. We found evidence to suggest that the first dredge-up mayplay a role in speeding up the rotation of the observable outer layersof giants and that the rotational velocity of horizontal branch stars islarger by a few km s-1 than that of first-ascent giants withsimilar mass, effective temperature, and radius. Finally, we found threegiants that rotate more rapidly than expected. We conjecture that theyacquired their excess angular momentum by ingesting planets.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 abundances of nearby red clump giants
Based on the analysis of high-resolution spectra with a highsignal-to-noise ratio, we have determined the abundances of theα-elements O, Si, Ca and Ti, the iron peak elements V, Fe and Ni,and the heavy element Ba without the consideration of non-localthermodynamic equilibrium (NLTE) effect and the light neutron-richelements Na, Mg and Al with an NLTE analysis for 63 nearby red clumpgiants. Fe abundances cover a logarithmic range between -0.60 and +0.35relative to solar. All abundance ratios with respect to Fe are similarto those found in the Sun. Hyperfine structure (HFS) was taken intoaccount when calculating V lines. The difference in abundances obtainedwith and without HFS can be as large as 0.5 dex.Based on observations collected at the European Southern Observatory(ESO) 1.52-m telescope at the La Silla Observatory in 2002 August.E-mail: gzhao@bao.ac.cn
| Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
Context: A radial velocity survey of about 380 G and K giant stars isongoing at Lick observatory. For each star we have a high signal tonoise ratio template spectrum, which we use to determine spectroscopicstellar parameters. Aims: The aim of this paper is to presentspectroscopic stellar parameters, i.e. effective temperature, surfacegravity, metallicity and rotational velocity for our sample of G and Kgiant stars. Methods: Effective temperatures, surface gravities andmetallicities are determined from the equivalent width of iron lines, byimposing excitation and ionisation equilibrium through stellaratmosphere models. Rotational velocities are determined from the fullwidth at half maximum (FWHM) of moderate spectral lines. A calibrationbetween the FWHM and total broadening (rotational velocity and macroturbulence) is obtained from stars in common between our sample and thesample from Gray (1989, ApJ, 347, 1021). Macro turbulence is determinedfrom the macro turbulence vs. spectral type relations from Gray (2005,The Observation and Analysis of Stellar Photospheres). Results: Themetallicity we derive is essentially equal to the literature values,while the effective temperature and surface gravity are slightly higherby 56 K and 0.15 dex, respectively. A method comparison is performedwith 72 giants in common with Luck & Heiter (2007, AJ, 133, 2464),which shows that both methods give similar results. Our rotationalvelocities are comparable with those obtained by Gray (1989, ApJ, 347,1021), but somewhat higher than those of de Medeiros & Mayor (1999,A&AS, 139, 433), which is consistent with the different diagnosticsused to determine them. Conclusions: We are able to determinespectroscopic stellar parameters for about 380 G and K giant starsuniformly (112 stars are being analysed spectroscopically for the firsttime). For stars available in the literature, we find reasonableagreement between literature values and values determined in the presentwork. In addition, we show that the metallicity enhancement of companionhosting stars might also be valid for giant stars, with the planethosting giants being 0.13 ± 0.03 dex (i.e. 35 ± 10%) moremetal rich than our total sample of stars.Based on data obtained at UCO/Lick Observatory, USA. Table 4 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1003
| Deriving temperature, mass, and age of evolved stars from high-resolution spectra. Application to field stars and the open cluster IC 4651
Aims.We test our capability of deriving stellar physical parameters ofgiant stars by analysing a sample of field stars and the well studiedopen cluster IC 4651 with different spectroscopic methods. Methods: Theuse of a technique based on line-depth ratios (LDRs) allows us todetermine with high precision the effective temperature of the stars andto compare the results with those obtained with a classical LTEabundance analysis. Results: (i) For the field stars we find that thetemperatures derived by means of the LDR method are in excellentagreement with those found by the spectral synthesis. This result isextremely encouraging because it shows that spectra can be used tofirmly derive population characteristics (e.g., mass and age) of theobserved stars. (ii) For the IC 4651 stars we use the determinedeffective temperature to derive the following results. a) The reddeningE(B-V) of the cluster is 0.12±0.02, largely independent of thecolor-temperature calibration used. b) The age of the cluster is1.2±0.2 Gyr. c) The typical mass of the analysed giant stars is2.0±0.2~Mȯ. Moreover, we find a systematicdifference of about 0.2 dex in log g between spectroscopic andevolutionary values. Conclusions: We conclude that, in spite of knownlimitations, a classical spectroscopic analysis of giant stars mayindeed result in very reliable stellar parameters. We caution that thequality of the agreement, on the other hand, depends on the details ofthe adopted spectroscopic analysis.Based on observations collected at the ESO telescopes at the Paranal andLa Silla Observatories, Chile.
| The Tennessee State University Automatic Spectroscopic Telescope: Data Processing and Velocity Variation of Cool Giants
This paper discusses data reduction for an echelle spectrograph we havedeveloped for an automatic telescope at Tennessee State University andare using to monitor radial velocities and line profiles of cool giantand supergiant stars. Although our approach to data reduction is ratherconventional, we discuss flat-fielding and extraction of velocities inways that should be of general interest, establish a transformation tothe IAU radial velocity system (+0.35 +/- 0.09 km s-1), anddetermine the external precision for measured velocities (0.10-0.11 kms-1). Also, we present results of the first 2-3 years ofmonitoring radial velocities in about 120 cool giants and compare thoseresults with the level of variability found with photometry. These newdata confirm the widely held understanding that K and M giants are allradial velocity variables at the level of 0.1 km s-1.
| Giants in the Local Region
We present parameter and abundance data for a sample of 298 nearbygiants. The spectroscopic data for this work have a resolution ofR~60,000, S/N>150, and spectral coverage from 475 to 685 nm. Overalltrends in the Z>10 abundances are dominated by Galactic chemicalevolution, while the light-element abundances are influenced by stellarevolution, as well as Galactic evolution. We find several super-Li starsin our sample and confirm that Li abundances in the first giant branchare related to mixing depths. Once astration of lithium on the mainsequence along with the overall range of main-sequence lithiumabundances are taken into account, the lithium abundances of the giantsare not dramatically at odds with the predictions of standard stellarevolution. We find the giants to be carbon-diluted in accord withstandard stellar evolution and that the carbon and oxygen abundancesdetermined for the local giants are consistent with those found in localfield dwarfs. We find that there is evidence for systematic carbonvariations in the red giant clump in the sense that the blue side of theclump is carbon-poor (more diluted) than the red side.
| 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.
| Basic physical parameters of a selected sample of evolved stars
We present the detailed spectroscopic analysis of 72 evolved stars,which were previously studied for accurate radial velocity variations.Using one Hyades giant and another well studied star as the referenceabundance, we determine the [Fe/H] for the whole sample. Thesemetallicities, together with the T_eff values and the absolute V-bandmagnitude derived from Hipparcos parallaxes, are used to estimate basicstellar parameters (ages, masses, radii, (B-V)0 and log g)using theoretical isochrones and a Bayesian estimation method. The(B-V)0 values so estimated turn out to be in excellentagreement (to within ~0.05 mag) with the observed (B-V), confirming thereliability of the T_eff-(B-V)0 relation used in theisochrones. On the other hand, the estimated log g values are typically0.2 dex lower than those derived from spectroscopy; this effect has anegligible impact on [Fe/H] determinations. The estimated diametersθ have been compared with limb darkening-corrected ones measuredwith independent methods, finding an agreement better than 0.3 maswithin the 1<θ<10 mas interval (or, alternatively, findingmean differences of just 6%). We derive the age-metallicity relation forthe solar neighborhood; for the first time to our knowledge, such arelation has been derived from observations of field giants rather thanfrom open clusters and field dwarfs and subdwarfs. The age-metallicityrelation is characterized by close-to-solar metallicities for starsyounger than ~4 Gyr, and by a large [Fe/H] spread with a trend towardslower metallicities for higher ages. In disagreement with other studies,we find that the [Fe/H] dispersion of young stars (less than 1 Gyr) iscomparable to the observational errors, indicating that stars in thesolar neighbourhood are formed from interstellar matter of quitehomogeneous chemical composition. The three giants of our sample whichhave been proposed to host planets are not metal rich; this result is atodds with those for main sequence stars. However, two of these starshave masses much larger than a solar mass so we may be sampling adifferent stellar population from most radial velocity searches forextrasolar planets. We also confirm the previous indication that theradial velocity variability tends to increase along the RGB, and inparticular with the stellar radius.
| 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.
| Sulphur abundances in disk stars as determined from the forbidden λ10821 [S I] line
Aims.In this paper we aim to study the chemical evolution of sulphur inthe galactic disk, using a new optimal abundance indicator: the [S i]line at 10821 Å. Similar to the optimal oxygen indicators, the [Oi] lines, the [S i] line has the virtues of being less sensitive to theassumed temperatures of the stars investigated and of likely being lessprone to non-LTE effects than other tracers.Methods.High-resolution, near-infrared spectra of the [S i] line arerecorded using the Phoenix spectrometer on the Gemini South telescope.The analysis is based on 1D, LTE model atmospheres using a homogeneousset of stellar parameters.Results.The λ10821 [S i] line issuitable for an abundance analysis of disk stars, and the sulphurabundances derived from it are consistent with abundances derived fromother tracers. We corroborate that, for disk stars, the trend ofsulphur-to-iron ratios with metallicity is similar to that found forother alpha elements, supporting the idea of a common nucleosyntheticorigin.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A New Definition for the Ca4227 Feature: Is Calcium Really Underabundant in Early-Type Galaxies?
We have investigated the abundance of calcium in early-type galaxies bymeasuring the strength of the Ca I λ4227 absorption line in theirintegrated spectra. The database used is the large sample of early-typegalaxy integrated spectra in Caldwell and coworkers. We have measured Caabundances from the Ca I λ4227 feature both by using the LickCa4227 index and by defining a new index, Ca4227r, thatavoids the CN4216 molecular band in the continuum on the blueward sideof the line. With the new index definition we measure Ca abundances thatare systematically ~0.3 dex higher than with the Lick Ca4227 index. Theresult is that with the new index definition we obtain higher [Ca/Fe]abundances in early-type galaxies, which are more consistent with theirwell-known [Mg/Fe] overabundances. Hence, we suggest that Ca might beslightly enhanced, relative to Fe, in early-type galaxies.
| Shapes of Spectral Line Bisectors for Cool Stars
The shape of the line bisector for the prototype spectral line Fe Iλ6253 was measured for an array of 54 stars on the cool half ofthe HR diagram. These bisectors are given in tables along with theirerrors. The classic C shape is shown by only a rather restricted rangein effective temperature and luminosity. The detailed change in bisectorshape with effective temperature and luminosity is documented moreprecisely than in previous work. The most blueward point on the bisectorchanges its height systematically with luminosity and can be used as aluminosity or gravity discriminant. The wide range of bisector shapescontains significant information about the velocity fields in theatmospheres of these stars, but extracting that information may requireextensive modeling.
| The epoch of the constellations on the Farnese Atlas and their origin in Hipparchus's lost catalogue
Not Available
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| 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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Spectral analysis of red clump giants and their use as standard candles in the wavebands I and K
Using high resolution and high signal-to-noise ratio observational data,we determined the stellar atmospheric parameters of 19 metal-poor redclump giants and their chemical abundances of the four α elements(i.e., O, Mg, Ca, Si). We discuss the variations, with the ironabundance, of the atmospheric parameters and of the α elementsabundances. We examined the absolute stellar magnitudes of 58 red clumpgiants in the I and K wavebands as well as their relations with the ironabundance, and found that for the analysed range of iron abundance, thecorrelation with the iron abundance is weaker for the absolute magnitudein the K band than that in the I band, in agreement with theoreticalexpectations.
| Determination of fundamental characteristics for stars of the F, G, and K spectral types. the surface gravities and metallicity parameters
We give some results of determination of the surface gravities andmetallicity parameters derived by the method of comparison of energydistributions in observed stellar spectra with calculated theoreticalones. Data of the Crimean, Pulkovo and Odesa catalogues are used.
| Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch
We present the results of our radial velocity (RV) measurements of G andK giants, concentrating on the presence of multiple systems in oursample. Eighty-three giants have been observed for 2.5 years with thefiber-fed echelle spectrograph FEROS at the 1.52 m ESO telescope in LaSilla, Chile. Seventy-seven stars (93%) of the targets have beenanalyzed for RV variability using simultaneous Th-Ar calibration and across-correlation technique. We estimate the long-term precision of ourmeasurement as better than 25 m s-1. Projected rotationalvelocities have been measured for most stars of the sample. Within ourtime-base only 21 stars (or 27%) show variability below 2\sigma, whilethe others show RV variability with amplitudes up to several kms-1. The large amplitude (several km s-1) andshape (high eccentricity) of the RV variations for 11 of the programstars are consistent with stellar companions, and possibly brown dwarfcompanions for two of the program stars. In those systems for which afull orbit could be derived, the companions have minimum masses from0.6 M\sun down to 0.1 M\sun. To thesemultiple systems we add the two candidates of giant planets alreadydiscovered in the sample. This analysis shows that multiple systemscontribute substantially to the long-term RV variability of giant stars,with about 20% of the sample being composed of multiple systems despitescreening our sample for known binary stars. After removing binaries,the range of RV variability in the whole sample clearly decreases, butthe remaining stars retain a statistical trend of RV variability withluminosity: luminous cool giants with B-V≥1.2 show RV variationswith \sigma_{/lineRV} > 60 m s-1, while giants with B-V< 1.2 including those in the clump region exhibit less variability orthey are constant within our accuracy. The same trend is observed withrespect to absolute visual magnitudes: brighter stars show a largerdegree of variability and, when plotted in the RV variability vs.magnitude diagram a trend of increasing RV scatter with luminosity isseen. The amplitude of RV variability does not increase dramatically, aspredicted, for instance, by simple scaling laws. At least two luminousand cooler stars of the sample show a correlation between RV andchromospheric activity and bisector asymmetry, indicating that in thesetwo objects RV variability is likely induced by the presence of(chromospheric) surface structures.Based on observations collected at the 1.52 m-ESO telescope at the LaSilla Observatory from Oct 1999 to Feb. 2002 under ESO programs and theESO-Observatório Nacional, Brazil, agreement and in part onobservations collected on the Alfred Jensch 2 m telescope of theThüringer Landessternwarte Tautenburg.
| 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.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| 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
| 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.
| 1-1.4 Micron Spectral Atlas of Stars
We present a catalog of J-band (1.08 to 1.35 μm) stellar spectra atlow resolution (R~400). The targets consist of 105 stars ranging inspectral type from O9.5 to M7 and luminosity classes I through V. Therelatively featureless spectra of hot stars, earlier than A4, can beused to remove the atmospheric features which dominate ground-basedJ-band spectroscopy. We measure equivalent widths for three absorptionlines and nine blended features which we identify in the spectra. Usingdetailed comparison with higher resolution spectra, we demonstrate thatlow-resolution data can be used for stellar classification, sinceseveral features depend on the effective temperature and gravity. Forexample, the CN index (1.096-1.104 μm) decreases with temperature,but the strength of a blended feature at 1.28 μm (consisting ofprimarily Pβ) increases. The slope of a star's spectrum can also beused to estimate its effective temperature. The luminosity class of astar correlates with the ratio of the Mg I (1.1831 μm) line to ablend of several species at 1.16 μm. Using these indicators, a starcan be classified to within several subclasses. Fifteen stars withparticularly high and low metal abundances are included in the catalog,and some spectral dependence on metal abundance is also found.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Line Absorption as a Metallicity Index for Giant Stars
The fraction of light removed from a star's spectrum by the spectrallines, the line absorption, is shown to be a precise empirical indicatorof metallicity. We measured the line absorption in 89 class III giantstars in a 42.5 Å window between 6219.0 and 6261.5 Å andthen calibrated these values against published metallicities. We showthat the line absorption can be measured precisely enough to improve themetallicity precision about fivefold over the original calibrationmetallicities, reaching a precision of 0.01 dex in favorable cases.
| Dating the Almagest star catalogue using proper motions : a reconsideration.
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Рибе |
| Ректацензија: | 23h17m09.94s |
| Deклинација: | +03°16'56.2" |
| Apparent магнитуда: | 3.703 |
| Proper motion RA: | 759.6 |
| Proper motion Dec: | 17.8 |
| B-T magnitude: | 4.845 |
| V-T magnitude: | 3.798 |
Каталог и designations:
|
