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Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| Dark matter in early-type galaxies: dynamical modelling of IC 1459, IC 3370, NGC 3379 and NGC 4105
We analyse long-slit spectra of four early-type galaxies which extendfrom ~1 to 3 effective radii: IC 1459; IC 3370; NGC 3379 and NGC 4105.We have extracted the full line-of-sight velocity distribution (in thecase of NGC 3379 we also used data from the literature), which we modelusing the two-integral approach. Using two-integral modelling, we findno strong evidence for dark haloes, but the fits suggest thatthree-integral modelling is necessary. We also find that the inferredconstant mass-to-light ratio in all the four cases is typical forearly-type galaxies. Finally, we also discuss the constraints on themass-to-light ratio, which can be obtained using X-ray haloes in thecase of IC 1459, NGC 3379 and NGC 4105, and compare the estimated valueswith the predictions from the dynamical modelling.
| UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar Spectra
We present an extended ultraviolet-blue (850-4700 Å) library oftheoretical stellar spectral energy distributions computed at highresolution, λ/Δλ=50,000. The UVBLUE grid, as wenamed the library, is based on LTE calculations carried out with ATLAS9and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800entries that cover a large volume of the parameter space. It spans arange in Teff from 3000 to 50,000 K, the surface gravityranges from logg=0.0 to 5.0 with Δlogg=0.5 dex, while sevenchemical compositions are considered:[M/H]=-2.0,-1.5,-1.0,-0.5,+0.0,+0.3, and +0.5 dex. For its coverageacross the Hertzsprung-Russell diagram, this library is the mostcomprehensive one ever computed at high resolution in theshort-wavelength spectral range, and useful application can be foreseenfor both the study of single stars and in population synthesis models ofgalaxies and other stellar systems. We briefly discuss some relevantissues for a safe application of the theoretical output to ultravioletobservations, and a comparison of our LTE models with the non-LTE (NLTE)ones from the TLUSTY code is also carried out. NLTE spectra are found,on average, to be slightly ``redder'' compared to the LTE ones for thesame value of Teff, while a larger difference could bedetected for weak lines, which are nearly wiped out by the enhanced coreemission component in case of NLTE atmospheres. These effects seem to bemagnified at low metallicity (typically [M/H]<~-1). A match with aworking sample of 111 stars from the IUE atlas, with availableatmosphere parameters from the literature, shows that UVBLUE modelsprovide an accurate description of the main mid- and low-resolutionspectral features for stars along the whole sequence from the B to ~G5type. The comparison sensibly degrades for later spectral types, withsupergiant stars that are in general more poorly reproduced than dwarfs.As a possible explanation of this overall trend, we partly invoke theuncertainty in the input atmosphere parameters to compute thetheoretical spectra. In addition, one should also consider the importantcontamination of the IUE stellar sample, where the presence of binaryand variable stars certainly works in the sense of artificiallyworsening the match between theory and observations.
| Nearby early-type galaxies with ionized gas. I. Line-strength indices of the underlying stellar population
With the aim of building a data-set of spectral properties of wellstudied early-type galaxies showing emission lines, we presentintermediate resolution spectra of 50 galaxies in the nearby Universe.The sample, which covers several of the E and S0 morphologicalsub-classes, is biased toward objects that might be expected to haveongoing and recent star formation, at least in small amounts, because ofthe presence of the emission lines. The emission is expected to comefrom the combination of active galactic nuclei and star formationregions within the galaxies. Sample galaxies are located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. Our long-slit spectra coverthe 3700-7250 Å wavelength range with a spectral resolution of≈7.6 Å at 5550 Å. The specific aim of this paper, and ourfirst step in the investigation, is to map the underlying galaxy stellarpopulation by measuring, along the slit positioned along the galaxymajor axis, line-strength indices at several, homogeneousgalacto-centric distances. For each object we extracted 7luminosity-weighted apertures (with radii 1.5´´,2.5´´, 10´´, r_e/10, r_e/8, r_e/4 and r_e/2)corrected for the galaxy ellipticity and 4 gradients (0 ≤ r ≤r_e/16, r_e/16 ≤ r ≤ r_e/8, r_e/8 ≤ r ≤ r_e/4 and r_e/4≤ r ≤ r_e/2). For each aperture and gradient we measured 25line-strength indices: 21 of the set defined by the Lick-IDS“standard” system (Trager et al. [CITE], ApJS, 116, 1) and 4introduced by Worthey & Ottaviani ([CITE], ApJS, 111, 377).Line-strength indices have been transformed to the Lick-IDS system.Indices derived then include Hβ, Mg1, Mg2, Mgb, MgFe, Fe5270,Fe5335 commonly used in classic index-index diagrams. The paperintroduces the sample, presents the observations, describes the datareduction procedures, the extraction of apertures and gradients, thedetermination and correction of the line-strength indices, the procedureadopted to transform them into the Lick-IDS System and the proceduresadopted for the emission correction. We finally discuss the comparisonsbetween our dataset and line-strength indices available in theliterature. A significant fraction, about 60%, of galaxies in thepresent sample has one previous measurement in the Lick-IDS system butbasically restricted within the r_e/8 region. Line-strength measuresobtained both from apertures and gradients outside this area and withinthe r_e/8 region, with the present radial mapping, are completely new.Full appendix and Figs. 8 to 13 are only available in electronic form athttp://www.edpsciences.org Full Tables 6, 7, 9 and 10 are only availableat the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/497 Based onobservations obtained at the European Southern Observatory, La Silla,Chile (Programs Nr. 60.A-0647 and 61.A-0406).
| 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.
| 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.
| The Ratio of α-Elements to Iron in Early-Type Galaxies from TIO and MG2
In order to derive the ratio of α-elements to iron in galaxies, wehave observed the strongest TiO band heads of the γ and γ'systems at 7000-7500 Å in a sample of a dozen early-type galaxies.The equivalent widths of the TiO bands are compared with syntheticspectra for single-aged stellar populations and composite galaxy models,all computed with [α/Fe]=0.0 and +0.3. The same method is alsoapplied to the and Mg2 Lick indices for the samplegalaxies. The results obtained are [Ti/Fe]~[Mg/Fe]~+0.3, indicating aclear enhancement of the α-elements-to-iron ratio for our sampleof early-type galaxies. Based on observations in the Observatóriodo Pico dos Dias, operated by the Laboratório Nacional deAstrofísica/CNPq/MCT, Brazil.
| Empirical calibration of the lambda 4000 Å break
Empirical fitting functions, describing the behaviour of the lambda 4000Ä break, D4000, in terms of effective temperature,metallicity and surface gravity, are presented. For this purpose, thebreak has been measured in 392 stars from the Lick/IDS Library. We havefollowed a very detailed error treatment in the reduction and fittingprocedures, allowing for a reliable estimation of the breakuncertainties. This calibration can be easily incorporated into stellarpopulation models to provide accurate predictions of the break amplitudefor, relatively old, composite systems. Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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
| 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.
| Integrated Ultraviolet Spectra and Line Indices of M31 Globular Clusters and the Cores of Elliptical Galaxies
We present observations of the integrated light of four M31 globularclusters (MIV, MII, K280, and K58) and of the cores of six ellipticalgalaxies (NGC 3605, 3608, 5018, 5831, 6127, and 7619) made with theFaint Object Spectrograph on the Hubble Space Telescope. The spectracover the range 2200-4800 Å at a resolution of 8 Å withsignal-to-noise ratio of more than 20 and flux accuracy of ~5%. To thesedata we add from the literature IUE observations of the dwarf ellipticalgalaxy M32, Galactic globular clusters, and Galactic stars. The stellarpopulations in these systems are analyzed with the aid of mid-UV andnear-UV colors and absorption line strengths. Included in the measuredindices is the key NH feature at 3360 Å. We compare these lineindex measures with the 2600 - 3000 colors of these stars and stellarpopulations. We find that the M31 globular clusters, Galactic globularclusters/Galactic stars, and elliptical galaxies represent threedistinct stellar populations, based on their behavior in color-linestrength correlations involving Mg II, NH, CN, and several UV metallicblends. In particular, the M31 globular cluster MIV, as metal-poor asthe Galactic globular M92, shows a strong NH 3360 Å feature. Otherline indices, including the 3096 Å blend that is dominated bylines of Mg I and Al I, show intrinsic differences as well. We also findthat the broadband line indices often employed to measure stellarpopulation differences in faint objects, such as the 4000 Å andthe Mg 2800 breaks, are disappointingly insensitive to these stellarpopulation differences. We find that the hot (T > 20,000 K) stellarcomponent responsible for the ``UV upturn'' at shorter wavelengths canhave an important influence on the mid-UV spectral range (2400-3200Å) as well. The hot component can contribute over 50% of the fluxat 2600 Å in some cases and affects both continuum colors and linestrengths. Mid-UV spectra of galaxies must be corrected for this effectbefore they can be used as age and abundance diagnostics. Of the threestellar populations studied here, M31 globular clusters and ellipticalgalaxies are more similar to each other than either is to the Galacticstellar populations defined by globular clusters and nearby stars.Similarities between the abundance-pattern differences currentlyidentified among these stellar populations and those among globularcluster stars (N, Al enhancements) present a curious coincidence thatdeserves future investigation. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| 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.
| The Abundance of CN. Calcium and Heavy Elements in High Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..825E&db_key=AST
| 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
| 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
| Star Streams and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1595E&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.
| 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.
| Spectral classification of symbiotic stars in the near infrared.
We present preliminary results of near infrared observations of 6 S typesymbiotic binaries, made with the aim of confirming and improvingprevious spectral classifications of the cool component. RepresentativeCCD spectra of some symbiotic and comparison stars in the region of theCaII infrared triplet are displayed. On our spectrograms at a dispersionof 33A/mm the FeI/TiII blend at 8469A and the FeI line at 8514A are moreuseful luminosity discriminants for symbiotics than the CaII triplet(8498, 8542 and 8662A) which is disturbed in some symbiotic spectra byemission components of the CaII triplet and of Paschen lines. Thetemperature classification of late M cool components can be reliablyderived from strengths of TiO and VO bands. Preliminary new spectraltypes and luminosity classes of six observed symbiotic stars aredescribed and discussed.
| The southern Vilnius photometric system. I - Transformation to the standard system
This paper is the first in a series on the extension of the Vilniusphotometric system to the southern hemisphere. Observations of a commonset of 73 stars measured in both hemispheres are described and ananalysis of the differences is given.
| Old stellar populations. IV - Empirical functions for features in the spectra of G and K stars
Empirical fitting functions are derived for 11 atomic and molecularfeatures prominent in the spectra of G and K stars. The fitting behaviorclosely mimics that expected from the physics of stellar atmospheres,except for the index CN (4150 A), for which only minimal evidence isfound for traditional gravity effects but strong evidence forevolutionary mixing of CNO products to the stellar surface. This findingis important for modeling the integrated CN indices of external stellarpopulations.
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| Spectral synthesis in the ultraviolet. IV - A library of mean stellar groups
A library of mean UV stellar energy distributions is derived from IUEspectrophotometry of 218 stars. The spectra cover 1230-3200 A with aspectral resolution of about 6 A. They have been corrected forinterstellar extinction and converted to a common flux and wavelengthscale. Individual stars were combined into standard groups according totheir continuum colors, observed UV spectral morphology, MK luminosityclass, and metal abundance. The library consists of 56 groups: 21dwarf(V), 8 subgiant(IV), 16 giant(III), and supergiant(I + II) groups,covering O3-M4 spectral types. A metal-poor sequence is included,containing four dwarf and two giant groups, as is a metal-enhancedsequence with a single dwarf, subgiant, and giant group. Spectralindices characterizing the continuum and several strong absorptionfeatures are examined as temperature, luminosity, and abundancediagnostics. The library is intended to serve as a basis forinterpreting the composite UV spectra of a wide variety of stellarsystems, e.g., elliptical galaxies, starburst systems, and high-redshiftgalaxies.
| A new library of stellar optical spectra
Attention is given to a new digital optical stellar library consistingof spectra covering 3510-8930 R at 11-A resolution for 72 differentstellar types. These types extend over the spectral classes O-M andluminosity classes I-V. Most spectra are of solar metallicity stars butsome metal-rich and metal-poor spectra are included. This new library isquantitatively compared to two previously published libraries. It offersseveral advantages over them: it is photometrically well-calibratedindividually and consistently from star to star. Good temperature andluminosity coverage has been achieved. The incorporation of stars withwell-determined temperature, metallicity, and surface gravity parametersincreases the accuracy of the spectral type assigned to each compositelibrary star.
| The magnesium Mg2 index as an indicator of metallicity in elliptical galaxies
A quantitative calibration of the Mg2 index is attempted deriving ametallicity scale for elliptical galaxies. The dependence of the indexon stellar temperature, gravity, and metallicity has been studiedthrough spectroscopic observations of 87 standards applying the derivedcalibration to models for stellar population synthesis. Buzzoni's (1989)computational code has been used to explore the behavior of the indexversus age, IMF, and metallicity of simple stellar populations,inferring galactic metallicity for the Davies et al. (1987) extensiveobservational database. It appears that ellipticals are old metal-richsystems, with age about 15 Gyr and (Fe/H) = + 0.15. A large spread ofnearly one order of magnitude is, however, derived for metallicity amongsingle galaxies confirming that (Fe/H) is the driving parameter inducingthe color spread in the galaxy population. Evolutionary behavior of Mg2is briefly discussed giving its expected variations at early epochs forcomparison with high-redshift galaxies.
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Osservazione e dati astrometrici
| Costellazione: | Bilancia |
| Ascensione retta: | 14h58m53.60s |
| Declinazione: | -11°08'39.0" |
| Magnitudine apparente: | 5.87 |
| Distanza: | 96.899 parsec |
| Moto proprio RA: | -107.1 |
| Moto proprio Dec: | -61.9 |
| B-T magnitude: | 7.533 |
| V-T magnitude: | 6.003 |
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INHABITED SKY
