내용
사진
사진 업로드
DSS Images Other Images
관련 글
Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| 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.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| 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 statistical search for supermetallicity in F, G and K stars
High-dispersion and low-resolution data are combined to search forsuper-metal-rich (SMR) FGK stars in the solar neighbourhood and Baade'sWindow. The data are assessed by using statistical analysis, with theirrms errors playing a key role. A star is considered to be SMR if itsvalue of [Fe/H]>+0.2dex, while `borderline' SMR status may beassigned if +0.1<[Fe/H]<=+0.2dex. Borderline SMR status isassigned to μ Leo and three other giants, but no full-fledged SMRgiants are found in either Baade's Window or the solar neighbourhood. Bycontrast, the existence of SMR class IV-V stars turns out to be wellestablished, with values found for [Fe/H] that are as large as ~+0.4dex.It is concluded that this apparent contrast between class IV-V stars andgiants should not be interpreted in astrophysical terms at presentbecause of marked shortcomings in the available data base for giants.Recommendations are made about future research that may cure thisproblem and extend present knowledge about SMR dwarfs.
| A Study of the Direct Fitting Method for Measurement of Galaxy Velocity Dispersions
We have measured the central stellar velocity dispersions of 33 nearbyspiral and elliptical galaxies, using a straightforward template-fittingalgorithm operating in the pixel domain. The spectra, obtained with theDouble Spectrograph at Palomar Observatory, cover both the Ca tripletand the Mg I b region, and we present a comparison of the velocitydispersion measurements from these two spectral regions. Model fits tothe Ca triplet region generally yield good results, with littlesensitivity to the choice of template star. In contrast, the Mg I bregion is more sensitive to template mismatch and to details of thefitting procedure, such as the order of a polynomial used to match thecontinuum shape of the template to the object. As a consequence of thecorrelation of the [Mg/Fe] ratio with velocity dispersion, it isdifficult to obtain a satisfactory model fit to the Mg I b lines and thesurrounding Fe blends simultaneously, particularly for giant ellipticalgalaxies with large velocity dispersions. We demonstrate that if themetallicities of the galaxy and template star are not well matched, thendirect template-fitting results are improved if the Mg I b linesthemselves are excluded from the fit and the velocity dispersion isdetermined from the surrounding weaker lines.
| Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocitydispersions for a sample of 148 early-type galaxies in differentenvironments. The wavelength region covered by the observations (lambda=~ 4600 to 6600 Å) includes the Lick/IDS indices Hβ,Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,Fe5709, Fe5782, NaD, TiO1 and TiO2. The data areintended to address possible differences of the stellar populations ofearly-type galaxies in low- and high-density environments. This paperdescribes the sample properties, explains the data reduction andpresents the complete list of all the measurements. Most galaxies of thesample (85%) had no previous measurements of any Lick/IDS indices andfor 30% of the galaxies we present first-time determinations of theirvelocity dispersions. Special care is taken to identify galaxies withemission lines. We found that 62 per cent of the galaxies in the samplehave emission lines, as measured by the equivalent width of the [OIII]5007Å line, EW[OIII] > 0.3 Å. Tables 5 and 6 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/395/431. They are also available via ftp atftp.mpe.mpg.de in the directory people/dthomas/Beuing02 or via WWW atftp://ftp.mpe.mpg.de/people/dthomas/Beuing02.
| Lick Spectral Indices for Super-Metal-rich Stars
We present Lick spectral indices for a complete sample of 139 candidatesuper-metal-rich stars of different luminosity classes (MK type from Ito V). For 91 of these stars we were able to identify, in anaccompanying paper, the fundamental atmosphere parameters. This confirmsthat at least 2/3 of the sample consists of stars with [Fe/H] in excessof +0.1 dex. Optical indices for both observations and fiducialsynthetic spectra have been calibrated to the Lick system according toWorthey et al. and include the Fe I indices of Fe5015, Fe5270, andFe5335 and the Mg I and MgH indices of Mg2 and Mg b at 5180Å. The internal accuracy of the observations is found to beσ(Fe5015)=+/-0.32 Å, σ(Fe5270)=+/-0.19 Å,σ(Fe5335)=+/-0.22 Å, σ(Mg2)=+/-0.004 mag,and σ(Mg b)=+/-0.19 Å. This is about a factor of 2 betterthan the corresponding theoretical indices from the synthetic spectra,the latter being a consequence of the intrinsic limitations in the inputphysics, as discussed by Chavez et al. By comparing models andobservations, we find no evidence for nonstandard Mg versus Fe relativeabundance, so [Mg/Fe]=0, on the average, for our sample. Both theWorthey et al. and Buzzoni et al. fitting functions are found tosuitably match the data and can therefore confidently be extended forpopulation synthesis application also to supersolar metallicity regimes.A somewhat different behavior of the two fitting sets appears, however,beyond the temperature constraints of our stellar sample. Its impact onthe theoretical output is discussed, as far as the integratedMg2 index is derived from synthesis models of stellaraggregates. A two-index plot, such as Mg2 versus Fe5270, isfound to provide a simple and powerful tool for probing distinctiveproperties of single stars and stellar aggregates as a whole. The majoradvantage, over a classical CM diagram, is that it is both reddeningfree and distance independent. Based on observations collected at theInstituto Nacional de Astrofísica, Optica y Electrónica(INAOE) ``G. Haro'' Observatory, Cananea (Mexico).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Observations and Atmospheric Parameters of Super-Metal-rich Candidates
The spectroscopic properties of a sample of 92 Population I bright stars(V<8) with literature values of [Fe/H]>=+0.1 are reviewed in orderto study the metallicity scale at supersolar regimes. For 73 of thesecandidate super-metal-rich (SMR) stars we identified the photosphericfiducial parameters (Teff, logg, [M/H]) from among publishedparameter sets via a comparison of new observations in the wavelengthrange 5034-5398 Å with synthetic spectra derived from the 1997database of Chavez et al. As a main issue in our analysis, we find thata ``genuine'' SMR stellar component in the Galactic disk exists withmore than one-fourth of the stars in our sample fulfilling the criterion[Fe/H]>=0.2 dex, and three of them as rich as [Fe/H]>+0.4 dex.Based on observations collected at the INAOE ``G. Haro'' Observatory,Cananea (Mexico).
| The stellar populations of early-type galaxies in the Fornax cluster
We have measured central line strengths for a magnitude-limited sampleof early-type galaxies in the Fornax cluster, comprising 11 elliptical(E) and 11 lenticular (S0) galaxies, more luminous thanMB=-17. When compared with single-burst stellar populationmodels we find that the centres of Fornax ellipticals follow a locus offixed age and have metallicities varying roughly from half solar totwice solar. The centres of (lower luminosity) lenticular galaxies,however, exhibit a substantial spread to younger luminosity-weightedages, indicating a more extended star formation history. Galaxies withold stellar populations show tight scaling relations between metal-lineindices and the central velocity dispersion. Remarkably also, the Felines are well correlated with σ0. Our detailedanalysis of the stellar populations suggests that these scalingrelations are driven mostly by metallicity. Galaxies with a youngstellar component do generally deviate from the main relation. Inparticular, the lower luminosity S0s show a large spread. Ourconclusions are based on several age/metallicity diagnostic diagrams inthe Lick/IDS system comprising established indices such asMg2 and Hβ as well as new and more sensitive indicessuch as HγA and Fe3, a combination of three prominentFe lines. The inferred difference in the age distribution betweenlenticular and elliptical galaxies is a robust conclusion, as the modelsgenerate consistent relative ages using different age and metallicityindicators, even though the absolute ages remain uncertain. The absoluteage uncertainty is mainly caused by the effects of non-solar abundanceratios which are not yet accounted for by the stellar population models.Furthermore, we find that elliptical galaxies and the bulge of onebright S0 are overabundant in magnesium, where the most luminousgalaxies show the strongest overabundances. The stellar populations ofyoung and faint S0s are consistent with solar abundance ratios or a weakMg underabundance. Two of the faintest lenticular galaxies in our samplehave blue continua and extremely strong Balmer-line absorption,suggesting star formation <2Gyr ago.
| Magnitudes absolues des étoiles standards MK des types G à M à partir des parallaxes Hipparcos. The absolute magnitudes of the G to M type MK standards from the Hipparcos parallaxes
We analyse a sample of about 500 MK standards of cool spectral types (Gto M) for to compare the visual absolute magnitudes obtained from bothHipparcos data and Schmidt-Kaler calibrations. Our purpose is tovalidate our spectroscopic work \cite[(Ginestet et al. 1997, 1999)]{G97}on stars with composite spectra with the help of Hipparcos data.Contrary to what is claimed in other papers, the absolute magnitudedomain devoted to the giant stars does not overlap the domain of dwarfs.We find that the discrepancies between absolute magnitudes fromHipparcos data and absolute magnitudes deduced from Schmidt-Kalercalibrations increase with the relative error sigma (pi )/pi on theparallaxes. So, for sigma (pi )/pi <= 0.05 only 3% of the starspresent a discrepancy of one luminosity class, while this percentagereaches 54% for 0.25 < sigma (pi )/pi <= 0.50. Curiously, theluminosity of the giants seems to increase with the distance of thestars, whereas the supergiants of the sample appear underluminous atleast for d < 600 pc! We point out a list of 14 MK standards whoseluminosity classes may be erroneous and need a new spectralclassification, in the near infrared. The case of composite-spectrumbinaries is also discussed. Most of these are too distant for accurateparallaxes even with Hipparcos: only sixteen stars have sigma (pi )/pi<= 0.10; for these, we give new spectral classifications in agreementwith both our classifications in the near infrared of the coolcomponents and Hipparcos data. Finally, for stars having high-precisionparallaxes (sigma (pi )/pi <= 5%) there is no serious problem forSchmidt-Kaler calibrations whith respect to Hipparcos data. The datacorresponding to parallaxes of lower precisions should be used withcaution and only for statistical analyses.
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Probing the {Na} BT I D and {K} BT I lambda 7699 resonance lines sensitivity to background opacity in late-type stars
We have measured the equivalent width WK of the K i resonanceline at 7699 Angstroms for a large sample of low activity late-typestars observed with high spectral resolution and we have verified thatthe relation WK vs. Teff is monotonicallydecreasing, for both dwarf and giant stars. This behaviour is differentfrom that of the Na I D lines for stars of the same type, which showedthat the relation WNa vs. Teff has a maximum forTeff ~ 4000 K, which is better defined for giants than fordwarfs (Tripicchio et al. 1997). The fit of the observed K I equivalentwidths by means of a NLTE spectral line synthesis using conventionalbackground opacity shows that, for dwarf stars, the adopted modelsoverestimate the observed WK for temperatures <~ 4000 K.This result is similar to that discussed for the Na I D lines in ourprevious paper. On the other hand, for giant stars with Teff<~ 3800 K these models in general underestimate WK. Thediscrepancies between observed and computed WK andWNa for cool stars are much stronger than the variations dueto uncertainties in either atmospheric model or line parameters, likeeffective temperature and surface gravity, or Van der Waals broadening.For M dwarf stars, the most convincing explanation for the disagreementis the lack of atomic and molecular line opacity in the adopted models.In fact, a NLTE spectral synthesis including an additional backgroundopacity reproduces with a good level of accuracy the equivalent widths,as well as the general shape of the profiles for both the Na I D and K Ilines, in a subsample of early-M dwarfs. Based on observations collectedat the European Southern Observatory (ESO), La Silla, Chile, and at theMcDonald Observatory, Mt. Locke, Texas, USA
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The NaI resonance lines as a spectroscopic test of late-type stellar atmospheres.
We have tested current models for the atmospheres (including photosphereand low chromosphere) of late-type stars using the D resonance lines ofneutral sodium as a diagnostic. To this end, we have measured theequivalent widths of the D lines for a sample of 39 dwarf and 45 giantlate-type stars observed with high spectral resolution. We constructedphotospheric models over a grid in effective temperature and surfacegravity spanning the spectral types F to M, and luminosity classes V andIII of the sample stars. The model photospheres were extended into thechromosphere by assuming a suitable scaling from the Sun, andtheoretical Nai D equivalent widths were computed over the grid ofmodels including the deviations from local thermodynamic equilibrium. Bytaking into account both the experimental errors and the possiblevariations of stellar parameters (effective temperature, surfacegravity, sodium abundance and microturbulence), the comparison betweenobserved and computed equivalent widths allows us to state that themodel atmospheres we have used can reproduce the observations for thetwo luminosity classes and for all the spectral types except for theM-type stars. We have discussed the importance of line blanketing in thespectral analysis of these stars, but at present we cannot conclude thatthis effect would reduce the discrepancy.
| Giants with infrared excess.
We have correlated optical and infrared catalogs in order to extract alarge sample of luminosity class III stars with known infrared fluxdensities. For a non-negligible fraction of G and K giants, afar-infrared excess emission was found, starting beyond 25μm. Anexplanation in terms of present-day mass loss thus becomes unlikely,since the dust should then be warmer and the excess emission less far inthe infrared. We believe that the far-infrared excesses of theseobjects, most likely first-ascent giants, are related to the Vegaphenomenon. The dusty disks around these stars, gradually cooled downduring their main-sequence phase, could be reheated once the star leavesthe main sequence and enters the luminous post-main-sequence phase. Thefairly large sample we constructed enables us to derive an estimationfor the occurrence of excesses. This fraction of G or K giants withfar-infrared excess appears to be distinctly smaller than amongmain-sequence stars. Since the higher radiation field of giants couldlead to a larger evaporation rate of the circumstellar debris, this factdoes not conflict with our hypothesis.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| Supermetallicity at the Quarter-Century Mark: A Conservative Statistician's Review of the Evidence
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..102..105T&db_key=AST
| New synthetic Mg2 indices
Using the most recent grid of Kurucz model atmospheres and his improvedset of numerical codes to compute synthetic stellar spectra, we havecalculated the strength of the magnesium absorption feature at 5175 A(Mg2 index) from a set of 141 computed synthetic spectra. The indexvalues refer to the effective temperature range 4000-6000 K, surfacegravity from 1.5 to 4.5 dex, and metallicity from -0.5 to 1.0 dex. Thecomputed index for the solar model matches very well the value obtainedfrom observational data. Above 5000 K, the new Mg2 values and previouscalculations agree to within 0.02 mag, but discrepancies can reachalmost 0.58 mag for cool, metal-rich, low-gravity stars, so that largevalues of Mg2 previously obtained for low temperature dwarfs are nowobtained for giants as well. A comparison with observational data isalso presented.
| Chemical Abundances for Very Strong-Lined Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2968L&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Abundances and velocities for open and globular cluster giants: The data.
We present a large dataset consisting of giants in the field, and inopen and globular clusters. A total of 122 giants were observed in thefields of 8 open clusters. A total of 342 giants were observed in thefields of 25 globular clusters. A total of 36 field stars with wellknown abundances and luminosities were also observed. Radial velocitiesare determined for most giants, some of which have no photometryavailable. We have analyzed several spectral features in order to definea grid that will allow the determination of metal abundances for haloand bulge giants. The errors involved in the determination of radialvelocities and [Fe/H] are carefully examined. We find that field andopen cluster stars on one side, and globular cluster giants on the otherside, do not follow the same calibration. This is possibly due toenhanced [α/Fe] abundances in globular clusters. Therefore, wehave defined a calibration based only on globular cluster giants, validfrom [Fe/H]=-2.0 to +0.5. This calibration is carried out with thepurpose of measuring metallicities for bulge and halo giants, with theunderlying assumption that the abundance ratios of the relevant elementsrelative to iron are similar to the calibrating stars. Adopting asstandards the globular clusters NGC 288, NGC 362, NGC 1851, NGC 6356,NGC 6624, 47 Tuc, M 4 , M 3, and M 22 we derive metallicities forglobular clusters with less well known compositions, like M 28, and NGC6637. In particular, we confirm a low metallicity for M 28([Fe/H]=-1.35+/-0.2), a cluster that has a disk orbit.
| SMR stars, strong-CN stars and R stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..103K&db_key=AST
| Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars
Twenty-one optical absorption features, 11 of which have been previouslydefined, are automatically measured in a sample of 460 stars. FollowingGorgas et al., the indices are summarized in fitting functions that giveindex strengths as functions of stellar temperature, gravity, and(Fe/H). This project was carried out with the purpose of predictingindex strengths in the integrated light of stellar populations ofdifferent ages and metallicities, but the data should be valuable forstellar studies in the Galaxy as well. Several of the new indices appearto be promising indicators of metallicity for old stellar populations. Acomplete list of index data and atmospheric parameters is available incomputer-readable form.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
