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Публикации по объекту
uvby-? photometry and kinematics of metal-poor stars: A search for moving groups in the Galactic Stellar Halo
The possible presence of moving groups in the local Galactic stellarhalo has been examined based on new uvby-? photometry for a sampleof 143 metal-poor stars joined to the photometry of 1553 stars from theprevious catalogues of Schuster & Nissen (1988), Schuster et al.(1993), and Schuster et al. (2006). This new set of photometric data,together with radial velocities and proper motions taken from theliterature, have allowed us to obtain Galactic space velocities U', V',and W' for nearly the entire sample. With this kinematic information,three diagrams: the [Fe/H] vs V_rot, the Bottlinger (V' vs U') and theToomre (V' vs (U'^2 + W'^2)^{1/2}) have been obtained and used toidentify probable groups of stars in common between them. Onceidentified, these groups were compared to moving groups reported in theliterature. In particular, probable members of the Kapteyn group and? Cen were identified.
| 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
| 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
| 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.
| 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.
| Population Synthesis in the Blue. IV. Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
We present a new set of model predictions for 16 Lick absorption lineindices from Hδ through Fe5335 and UBV colors for single stellarpopulations with ages ranging between 1 and 15 Gyr, [Fe/H] ranging from-1.3 to +0.3, and variable abundance ratios. The models are based onaccurate stellar parameters for the Jones library stars and a new set offitting functions describing the behavior of line indices as a functionof effective temperature, surface gravity, and iron abundance. Theabundances of several key elements in the library stars have beenobtained from the literature in order to characterize the abundancepattern of the stellar library, thus allowing us to produce modelpredictions for any set of abundance ratios desired. We develop a methodto estimate mean ages and abundances of iron, carbon, nitrogen,magnesium, and calcium that explores the sensitivity of the variousindices modeled to those parameters. The models are compared to high-S/Ndata for Galactic clusters spanning the range of ages, metallicities,and abundance patterns of interest. Essentially all line indices arematched when the known cluster parameters are adopted as input.Comparing the models to high-quality data for galaxies in the nearbyuniverse, we reproduce previous results regarding the enhancement oflight elements and the spread in the mean luminosity-weighted ages ofearly-type galaxies. When the results from the analysis of blue and redindices are contrasted, we find good consistency in the [Fe/H] that isinferred from different Fe indices. Applying our method to estimate meanages and abundances from stacked SDSS spectra of early-type galaxiesbrighter than L*, we find mean luminosity-weighed ages of theorder of ~8 Gyr and iron abundances slightly below solar. Abundanceratios, [X/Fe], tend to be higher than solar and are positivelycorrelated with galaxy luminosity. Of all elements, nitrogen is the morestrongly correlated with galaxy luminosity, which seems to indicatesecondary nitrogen enrichment. If that interpretation is correct, thisresult may impose a lower limit of 50-200 Myr to the timescale of starformation in early-type galaxies. Unlike clusters, galaxies show asystematic effect whereby higher order, bluer, Balmer lines yieldyounger ages than Hβ. This age discrepancy is stronger for lowerluminosity galaxies. We examine four possible scenarios to explain thistrend. Contamination of the bluer indices by a metal-poor stellarpopulation with a blue horizontal branch cannot account for the data.Blue stragglers and abundance-ratio effects cannot be ruled out, as theycan potentially satisfy the data, even though this can only be achievedby resorting to extreme conditions, such as extremely high [O/Fe] orspecific blue-straggler frequencies. The most likely explanation is thepresence of small amounts of a young/intermediate-age stellar populationcomponent. We simulate this effect by producing two-component models andshow that they provide a reasonably good match to the data when the massfraction of the young component is typically a few percent. Ifconfirmed, this result implies star formation has been extended inearly-type galaxies, and more so in less massive galaxies, which seemsto lend support to the ``downsizing'' scenario. Moreover, it impliesthat stellar population synthesis models are capable of constraining notonly the mean ages of stellar populations in galaxies, but also theirage spread.
| 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.
| 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.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| 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.
| 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
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries
We report 25,563 radial velocity measurements for 1359 single-linedstars in the Carney-Latham sample of 1464 stars selected for high propermotion. For 171 of these, we present spectroscopic orbital solutions. Wefind no obvious difference between the binary characteristics in thehalo and the disk populations. The observed frequency is the same, andthe period distributions are consistent with the hypothesis that the twosets of binaries were drawn from the same parent population. Thissuggests that metallicity in general, and radiative opacities inparticular, have little influence over the fragmentation process thatleads to short-period binaries. All the binaries with periods shorterthan 10 days have nearly circular orbits, while the binaries withperiods longer than 20 days exhibit a wide range of eccentricities and amedian value of 0.37. For the metal-poor high-velocity halo binaries inour sample, the transition from circular to eccentric orbits appears tooccur at about 20 days, supporting the conclusion that tidalcircularization on the main sequence is important for the oldestbinaries in the Galaxy. Some of the results presented here usedobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| 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.
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| A survey of proper motion stars. 12: an expanded sample
We report new photometry and radial velocities for almost 500 stars fromthe Lowell Proper Motion Catalog. We combine these results with ourprior sample and rederive stellar temperatures based on the photometry,reddening, metallicities (using chi squared matching of our 22,500 lowSignal to Noise (S/N) high resolution echelle spectra with a grid ofsynthetic spectra), distances, space motions, and Galactic orbitalparameters for 1269 (kinematics) and 1261 (metallicity) of the 1464stars in the complete survey. The frequency of spectroscopic binariesfor the metal-poor ((m/H) less than or equal to -1.2) stars with periodsshorter than 3000 days is at least 15%. The spectroscopic binaryfrequency for metal-rich stars ((m/H) greater than -0.5) appears to belower, about 9%, but this may be a selection effect. We also discussspecial classes of stars, including treatment of the double-linedspectroscopic binaries, and identification of subgiants. Four possiblenew members of the class of field blue stragglers are noted. We pointout the detection of three possible new white dwarfs, six broad-lined(binary) systems, and discuss briefly the three already knownnitrogen-rich halo dwarfs. The primary result of this paper will beavailable on CD-ROM, in the form of a much larger table.
| High-tangential-velocity stars
Two lists of high tangential velocity (greater than 100 km/s) starscontained in the Lowell Northern Hemisphere proper motion surveycatalogue have been compiled, the stellar distances being inferred fromeither trigonometric or spectroscopic parallaxes. The information givenincludes equatorial coordinates, corrected photographic magnitudes,proper motions, trigonometric or spectroscopic parallaxes, and spectraltypes.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 10h50m56.63s |
| Склонение: | +53°14'51.2" |
| Видимая звёздная величина: | 10.44 |
| Собственное движение RA: | -222.1 |
| Собственное движение Dec: | -186.3 |
| B-T magnitude: | 10.928 |
| V-T magnitude: | 10.481 |
Каталоги и обозначения:
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