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C II Abundances in Early-Type Stars: Solution to a Notorious Non-LTE Problem
We address a long-standing discrepancy between non-LTE analyses of theprominent C II 4267 and 6578/82 Å multiplets in early-type stars.A comprehensive non-LTE model atom of C II is constructed based oncritically selected atomic data. This model atom is used for anabundance study of six apparently slow-rotating main-sequence and giantearly B-type stars. High-resolution and high S/N spectra allow us toderive highly consistent abundances not only from the classical featuresbut also from up to 18 additional C II lines in the visual-including twoso far unreported emission features equally well reproduced in non-LTE.These results require the stellar atmospheric parameters to bedetermined with care. A homogeneous (slightly) subsolar present-daycarbon abundance from young stars in the solar vicinity (in associationsand in the field) of log(C/H)+12=8.29+/-0.03 is indicated.
| The epoch of the constellations on the Farnese Atlas and their origin in Hipparchus's lost catalogue
Not Available
| 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 total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| 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
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 148: HR 7955
Not Available
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| An All-Sky Catalog of Faint Extreme Ultraviolet Sources
We present a list of 534 objects detected jointly in the ExtremeUltraviolet Explorer (EUVE) 100 Angstroms all-sky survey and in theROSAT X-Ray Telescope 0.25 keV band. The joint selection criterionpermits use of a low count rate threshold in each survey. This lowthreshold is roughly 60% of the threshold used in the previous EUVEall-sky surveys, and 166 of the objects listed here are new EUV sources,appearing in neither the Second EUVE Source Catalog nor the ROSAT WideField Camera Second Catalog. The spatial distribution of this all-skycatalog shows three features: an enhanced concentration of objects inUrsa Major, where the Galactic integrated H I column reaches its globalminimum; an enhanced concentration in the third quadrant of the Galaxy(lII from 180 deg to 270 deg) including the Canis Major tunnel, whereparticularly low H I columns are found to distances beyond 200 pc; and aparticularly low number of faint objects in the direction of the fourthquadrant of the Galaxy, where nearby intervening H I columns areappreciable. Of particular interest is the composition of the 166detections not previously reported in any EUV catalog. We offerpreliminary identifications for 105 of these sources. By far the mostnumerous (81) of the identifications are late-type stars (F, G, K, M),while 18 are other stellar types, only five are white dwarfs (WDs), andnone are extragalactic. The paucity of WDs and extragalactic objects maybe explained by a strong horizon effect wherein interstellar absorptionstrongly limits the effective new-source search volume and, thereby,selectively favors low-luminosity nearby sources over more luminous butdistant objects.
| Fundamental Stellar Parameters of gamma 2 Velorum from HIPPARCOS Data
We report parallax measurements by the HIPPARCOS satellite of gamma 2Velorum and a few related objects. The distance of gamma 2 Vel is d =258 ^{+41}_{-31} pc, significantly smaller than the commonly adoptedvalue to Vela OB2. For zeta Puppis d = 429 ^{+120}_{-77} pc is inagreement with the canonical distance. The total mass of gamma 2 Velderived from its parallax, the angular size of the semimajor axis asmeasured with intensity interferometry, and the period are M(W-R + O) =29.5 +/- 15.9 Msolar. This result favors the orbital solution of Pike etal. over that of Moffat et al. The stellar parameters for the O starcompanion derived from line-blanketed non-LTE atmosphere models are Teff= 34,000 +/- 1500 K, log L/Lsolar = 5.3 +/- 0.15, from which anevolutionary mass of M = 29 +/- 4 Msolar and an age of 4.0^{+0.8}_{-0.5} Myr is obtained from single-star evolutionary models.With non-LTE model calculations including He and C, we derive aluminosity log L/Lsolar ~ 4.7 +/- 0.2 for the W-R star. Themass-luminosity relation of hydrogen-free W-R stars implies a mass ofMW-R ~ 5 +/- 1.5 Msolar. From our data we favor an age of about 10 Myrfor the bulk of the Vela OB2 stars. Evolutionary scenarios for zeta Pupand gamma 2 Vel are discussed in the light of our results.
| 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
| Transformations from Theoretical Hertzsprung-Russell Diagrams to Color-Magnitude Diagrams: Effective Temperatures, B-V Colors, and Bolometric Corrections
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...469..355F&db_key=AST
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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.
| Interstellar NaI absorption towards stars in the region of the IRAS VELA shell.
Not Available
| Chemical abundances in early B-type stars. 5: Metal abundances and LTE/NLTE comparison
Chemical abundances of neon, magnesium, aluminum, sulfur, and iron arederived for a sample of 21 unevolved B-stars in the local field andnearby associations. While aluminum, sulfur, and iron are underabundantin nearly all stars, near solar abundances are found for magnesium andneon. In agreement with earlier results for carbon, nitrogen, oxygen,and silicon (Kilian 1992), the present results show no correlation withsurface gravities or evolutionary states, which indicates that the metalabundances reflect the original composition of the interstellar medium.The results are supplemented by a comparison of local thermodynamicequilibrium (LTE) and non-LTE (NLTE) abundances for C, N, O, Si, Mg, andAl. In most cases the differences amount to +/- (0.1-0.2) dex, whichslightly exceeds the estimated accuracy of the NLTE abundancedetermination. However, a clear temperature gradient is evident for mostelements, which indicates systematic LTE abundance errors with a maximumamplitude of 0.4 dex between 21 000 K and 31 000 K.
| Rotational velocity of Be stars correlated with extinction law
The paper presents the comparison of the extinction curves extractedfrom spectra of 35 Be stars. It is suggested that high rotationalvelocity relates to 'peculiar' shape of extinction curve i.e., the lackof the 2200 A bump. This phenomenon occurs only if the total reddeningis not very high. We assume that such extinction curves originate solelyin circumstellar disks surrounding the high rotational velocity stars.Other objects are probably also obscured by some additional interstellarclouds.
| On the determination of effective temperature and surface gravity of B, A, and F stars using Stromgren UVBY beta photometry
The determination of stellar temperatures and surface gravities by meansof the Stromgren uvby beta photometric system is examined in the regionof main sequence stars. We used a sample of stars with independentlyderived temperatures and gravities. In particular, the calibrations ofMoon & Dworetsky (1985), Lester et al. (1986), and Balona (1984) arediscussed. We compare our results with Castelli (1991) and present newtemperature calibrations for normal, Johnson, and Ap stars. The use ofintegrated fluxes and especially the infrared flux method fordetermining stellar temperatures is discussed. Surface gravities of Band A stars, derived by fitting theoretical profiles to the Balmerlines, are used to check the calibrations.
| 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.
| The quantitative assessment of UV extinction derived from IUE data of giants and supergiants
It is shown here that the UV interstellar extinction towards hotluminous stars can be determined as accurately as for hot main-sequencestars. An atlas of IUE dereddened fluxes is presented for 13 lightlyreddened stars within the 1160-3125 A range. The fluxes of these starshow absorption line strengths that allow a rather accurate determinationof relative temperatures and luminosities which is more suitable for thedetermination of UV extinction via the pair method than choosing acomparison star based on quoted optical MK classifications.
| Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
| Chemical abundances in early B-type stars. IV - He, CNO, and SI abundances
Chemical abundances of 21 unevolved B-stars in the local field andnearby associations are given. LTE model atmospheres and non-LTE lineformation calculations were used for the abundance determination of He,C, N, O, and Si. A comparison with evolutionary tracks from Maeder &Meynet (1988) shows that all stars are near the main sequence. In theatmospheres of two stars processed matter has been detected, which canbe explained by the assumption of fast rotation. Differences in theobserved abundances lead to the conclusion that the interstellar matteris well mixed on a large scale but inhomogeneous on a small scale.
| The surface-brightness method and the dependence of the bolometric correction on star effective temperature.
Not Available
| The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification
Empirical effective temperature of 211 early-type stars found in aprevious investigation (Kontizas and Theodossiou, 1980; Theodossiou,1985) are combined with the effective temperatures of 313 early-typestars from the literature. From these effective temperatures of a totalnumber of 524 early-type stars of spectral types from O8 to F6 a newstellar temperature scale is developed along with the standard deviationof the MK spectral classification.
| Chemical abundances in early B-type stars. III - NLTE temperature and gravity determination
Effective temperatures Teff and gravities log g of l9 unevolved B starsin the local field and nearby associations are given. Determinations ofTeff due to non-LTE analyses of silicon line formation and non-LTEanalyses of helium line formation are compared, and a reasonableagreement is obtained. Small differences were observed for four B starsonly. The temperature calibration of some important photometricobservables is discussed, with particular emphasis on a comparison withsynthetic spectral indices. Temperatures obtained from thenonthermodynamic ionization equilibria of helium and silicon were foundto be systematically higher by 2000 K than those calculated fromsynthetic photometry and LTE assumptions.
| 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.
| The interstellar medium in the solar vicinity - Analysis of the distribution of colour excesses E(b-y) towards 10 selected areas
The distribution of color excesses, E(b-y), and the distances to about680 stars (mainly of spectral types A and F belonging to ten Kapteyn'sselected areas) are analyzed in order to investigate some of thereddening properties of the interstellar obscuring matter in the solarvicinity. Particular attention among these areas is given to sevenregions with line-of-sight toward the Gum Nebula and the interfacebetween the Local and Loop I Bubbles. It is shown that the Gum Nebulaand the interface between the Local Bubble and the Loop I Bubble arelikely to be the main sources of the diffuse absorbing material in thedirection of the seven low-galactic-latitude areas analyzed.
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
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Osservazione e dati astrometrici
| Costellazione: | Poppa |
| Ascensione retta: | 07h49m14.30s |
| Declinazione: | -46°22'24.0" |
| Magnitudine apparente: | 4.11 |
| Distanza: | 602.41 parsec |
| Moto proprio RA: | -3.5 |
| Moto proprio Dec: | 9.6 |
| B-T magnitude: | 3.846 |
| V-T magnitude: | 4.056 |
Cataloghi e designazioni:
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