Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

25 Cet



Upload your image

DSS Images   Other Images

Related articles

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.

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.

Testing stellar population models with star clusters in the Large Magellanic Cloud
We present high signal-to-noise ratio integrated spectra of 24 starclusters in the Large Magellanic Cloud (LMC), obtained using the FLAIRspectrograph at the UK Schmidt telescope. The spectra have been placedon to the Lick/IDS system in order to test the calibration of SimpleStellar Population (SSP) models. We have compared the SSP-predictedmetallicities of the clusters with those from the literature,predominantly taken from the Ca-triplet spectroscopy of Olszewski et al.(1991). We find that there is good agreement between the metallicitiesin the range -2.10 <=[Fe/H]<= 0. However, the Mg2 index(and to a lesser degree Mg b) systematically predict highermetallicities (up to +0.5 dex higher) than . Among thepossible explanations for this are that the LMC clusters possess[α/Fe] > 0. Metallicities are presented for eleven LMC clusterswhich have no previous measurements. We compare SSP ages for theclusters, derived from the Hβ, Hγ and Hδ Lick/IDSindices, with the available literature data, and find good agreement forthe vast majority. This includes six old globular clusters in oursample, which have ages consistent with their HST colour-magnitudediagram (CMD) ages and/or integrated colours. However, two globularclusters, NGC 1754 and NGC 2005, identified as old (~15 Gyr) on thebasis of HST CMDs, have Hβ line-strengths which lead ages that aretoo low (~8 and ~6 Gyr respectively). These findings are inconsistentwith their CMD-derived values at the 3σ level. Comparison betweenthe horizontal branch morphology and the Balmer line strengths of theseclusters suggests that the presence of blue horizontal branch stars hasincreased their Balmer indices by up to ~1.0 Å. We conclude thatthe Lick/IDS indices, used in conjunction with contemporary SSP models,are able to reproduce the ages and metallicities of the LMC clustersreassuringly well. The required extrapolations of the fitting functionsand stellar libraries in the models to lower ages and low metallicitiesdo not lead to serious systematic errors. However, owing to thesignificant contribution of horizontal branch stars to Balmer indices,SSP model ages derived for metal-poor globular clusters are ambiguouswithout a priori knowledge of horizontal branch morphology.

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 ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521

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( 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 ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

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.

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 (, or viahttp://cdsweb.u-strasbg.fr/Abstract.html

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.

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.

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 critical appraisal of published values of (Fe/H) for K II-IV stars
'Primary' (Fe/H) averages are presented for 373 evolved K stars ofluminosity classes II-IV and (Fe/H) values beween -0.9 and +0.21 dex.The data define a 'consensus' zero point with a precision of + or -0.018 dex and have rms errors per datum which are typically 0.08-0.16dex. The primary data base makes recalibration possible for the large(Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989).A set of (Fe/H) standard stars and a new DDO calibration are given whichhave rms of 0.07 dex or less for the standard star data. For normal Kgiants, CN-based values of (Fe/H) turn out to be more precise than manyhigh-dispersion results. Some zero-point errors in the latter are alsofound and new examples of continuum-placement problems appear. Thushigh-dispersion results are not invariably superior to photometricmetallicities. A review of high-dispersion and related work onsupermetallicity in K III-IV star is also given.

High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
A high-resolution spectroscopic survey of 671 G and K field giants isdescribed. Broad-band Johnson colors have been calibrated againstrecent, accurate effective temperature, T(eff), measurements for starsin the range 3900-6000 K. A table of polynomial coefficients for 10color-T(eff) relations is presented. Stellar atmosphere parameters,including T(eff), log g, Fe/H, and microturbulent velocity, are computedfor each star, using the high-resolution spectra and various publishedphotometric catalogs. For each star, elemental abundances for a varietyof species have been computed using a LTE spectrum synthesis program andthe adopted atmosphere parameters.

Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet
The morphology of 218 mid-UV spectra of stars ranging from O through Kin spectral type is examined. Several new line and continuum indices aredefined and their usefulness as temperature, luminosity, and metallicitydiscriminants is discussed. Mid-UV stellar continua are found to bemarkedly affected by abundance. A UV excess, delta(2600-V), is computedwhich is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B).The relative strength of spectral lines in the mid-UV is not as stronglyaffected by abundance. Mid-UV spectra are much more sensitive to thetemperature of the stellar population than to either metallicity or thedwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying nosensitivity to abundance for cool stars and a reversed sensitivity in FGdwarfs such that metal-poor stars have stronger Mg II strengths at thesame temperature than more metal-rich stars.

Large and kinematically unbiased samples of G- and K-type stars. IV - Evolved stars of the old disk population
Modified Stromgren and (R,I) photometry, along with DDO and Genevaphotometry, are presented for a complete sample of evolved old-disk Gand K giants in the Bright Star Catalogue. Stars with ages of between1.5 x 10 to the 9th and 10 to the 10th yr are found to have anear-normal distribution of heavy element abundances, centered on anFe/H abundance ratio of -0.1 dex. The old disk clusters NGC 3680 and IC4651 contain red-straggler young-disk giants that are probablycontemporaries of the blue stragglers in the clusters.

Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.

A search for lithium-rich giant stars
Lithium abundances or upper limits have been determined for 644 brightG-K giant stars selected from the DDO photometric catalog. Two of thesegiants possess surface lithium abundances approaching the 'cosmic' valueof the interstellar medium and young main-sequence stars, and eight moregiants have Li contents far in excess of standard predictions. At leastsome of these Li-rich giants are shown to be evolved to the stage ofhaving convectively mixed envelopes, either from the direct evidence oflow surface carbon isotope ratios, or from the indirect evidence oftheir H-R diagram positions. Suggestions are given for the uniqueconditions that might have allowed these stars to produce or accrete newlithium for their surface layers, or simply to preserve from destructiontheir initial lithium contents. The lithium abundance of the remainingstars demonstrates that giants only very rarely meet the expectations ofstandard first dredge-up theories; the average extra Li destructionrequired is about 1.5 dex. The evolutionary states of these giants andtheir average masses are discussed briefly, and the Li distribution ofthe giants is compared to predictions of Galactic chemical evolution.

Old stellar populations. II - an analysis of K-giant spectra
Eleven strong absorption features are studied in a sample of 110 K-giantstars, based on spectra taken at 9-A resolution, including such featuresas CN 4170 A, G-band, H-beta, Mg b, MgH, two Fe lines, NaD, and two TiObands. The surface features sensitive to surface gravity are determined;it is noted that the most accurate gravity indicator appears to be theindex Mg2. Previously identified super metal-rich stars generally showthe strongest lines of iron, CN, Mg, and NaD; essentially allintermediate and strong blends are also markedly enhanced in thesestars. Finally, iron-line residual Delta-Fe is shown to be a goodmeasure of metallicity and at the same time independent of surfacegravity.

UVBY BET photometry of equatorial and southern bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27...47H&db_key=AST

Determination of atmospheric parameters for G and K giants by means of photoelectric indices.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....15..123H&db_key=AST

Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST

Micrometer measures of companions to bright stars.
Not Available

A Catalogue of High-Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2..195R&db_key=AST

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:01h03m02.60s
Apparent magnitude:5.43
Distance:125.786 parsecs
Proper motion RA:-116.4
Proper motion Dec:-103
B-T magnitude:6.829
V-T magnitude:5.532

Catalogs and designations:
Proper Names   (Edit)
Flamsteed25 Cet
HD 1989HD 6203
TYCHO-2 2000TYC 4683-2266-1
USNO-A2.0USNO-A2 0825-00243780
BSC 1991HR 296

→ Request more catalogs and designations from VizieR