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Early-type stars observed in the ESO UVES Paranal Observatory Project - I. Interstellar NaI UV, TiII and CaII K observations*
We present an analysis of interstellar NaI (λair=3302.37 and 3302.98 Å), TiII(λair= 3383.76Å) and CaII K (λair= 3933.66 Å) absorptionfeatures for 74 sightlines towards O- and B-type stars in the Galacticdisc. The data were obtained from the Ultraviolet and Visual EchelleSpectrograph Paranal Observatory Project, at a spectral resolution of3.75 km s-1 and with mean signal-to-noise ratios per pixel of260, 300 and 430 for the NaI, TiII and CaII observations, respectively.Interstellar features were detected in all but one of the TiIIsightlines and all of the CaII sightlines. The dependence of the columndensity of these three species with distance, height relative to theGalactic plane, HI column density, reddening and depletion relative tothe solar abundance has been investigated. We also examine the accuracyof using the NaI column density as an indicator of that for HI. Ingeneral, we find similar strong correlations for both Ti and Ca, andweaker correlations for Na. Our results confirm the general belief thatTi and Ca occur in the same regions of the interstellar medium (ISM) andalso that the TiII/CaII ratio is constant over all parameters. We henceconclude that the absorption properties of Ti and Ca are essentiallyconstant under the general ISM conditions of the Galactic disc.
| High-resolution spectroscopy of the old open cluster Collinder 261: abundances of iron and other elements
We present the analysis of high resolution spectra of six red giantstars in the old open cluster Collinder 261. Reddening values forindividual stars, derived from the relation between colours andtemperatures (deduced from our fully spectroscopic analysis) areconsistent with previous determinations based on photometry. For thiscluster we derive an iron abundance of [Fe/H] = - 0.03 ± 0.03. Wealso obtain the abundances of light metals (O, Na and Al),α-elements (Mg, Si, Ca, Ti), elements of the Fe-group (Sc, Cr, Mn,Co, Ni) and the neutron-capture element Ba. No intrinsic star-to-starscatter is present in any of these elements within our sample. Wecompare our findings with previous investigations on this cluster,discussing in detail differences in analysis methods and results.
| Asphericity and clumpiness in the winds of Luminous Blue Variables
We present the first systematic spectropolarimetric study of LuminousBlue Variables (LBVs) in the Galaxy and the Magellanic Clouds, in orderto investigate the geometries of their winds. We find that at least halfof our sample show changes in polarization across the strong Hαemission line, indicating that the light from the stars is intrinsicallypolarized and therefore that asphericity already exists at the base ofthe wind. Multi-epoch spectropolarimetry on four targets revealsvariability in their intrinsic polarization. Three of these, AG Car, HRCar and P Cyg, show a position angle (PA) of polarization which appearsrandom with time. Such behaviour can be explained by the presence ofstrong wind-inhomogeneities, or “clumps” within the wind.Only one star, R 127, shows variability at a constant PA, and henceevidence for axi-symmetry as well as clumpiness. However, if viewed atlow inclination, and at limited temporal sampling, such a wind wouldproduce a seemingly random polarization of the type observed in theother three stars. Time-resolved spectropolarimetric monitoring of LBVsis therefore required to determine if LBV winds are axi-symmetric ingeneral. The high fraction of LBVs (>50%) showing intrinsicpolarization is to be compared with the lower ~20-25% for similarstudies of their evolutionary neighbours, O supergiants and Wolf-Rayetstars. We anticipate that this higher incidence is due to the lowereffective gravities of the LBVs, coupled with their variabletemperatures within the bi-stability jump regime. This is alsoconsistent with the higher incidence of wind asphericity that we find inLBVs with strong Hα emission and recent (last ~10 years) strongvariability.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Multicomponent radiatively driven stellar winds. II. Gayley-Owocki heating in multitemperature winds of OB stars
We show that the so-called Gayley-Owocki (Doppler) heating is importantfor the temperature structure of the wind of main sequence stars coolerthan the spectral type O6. The formula for Gayley-Owocki heating isderived directly from the Boltzmann equation as a direct consequence ofthe dependence of the driving force on the velocity gradient. SinceGayley-Owocki heating deposits heat directly on the absorbing ions, wealso investigated the possibility that individual components of theradiatively driven stellar wind have different temperatures. This effectis negligible in the wind of O stars, whereas a significant temperaturedifference takes place in the winds of main sequence B stars for starscooler than B2. Typical temperature differences between absorbing ionsand other flow components for such stars is of the order 103K. However, in the case when the passive component falls back onto thestar, the absorbing component reaches temperatures of order106 K, which allows for emission of X-rays. Moreover, wecompare our computed terminal velocities with the observed ones. Wefound quite good agreement between predicted and observed terminalvelocities. The systematic difference coming from the using of the socalled ``cooking formula'' has been removed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| On the nature of the bi-stability jump in the winds of early-type supergiants
We study the origin of the bi-stability jump in the terminal velocity ofthe winds of supergiants near spectral type B1. Observations show thathere the ratio {v_infty/v_esc} drops steeply from about 2.6 at typesearlier than B1 to a value of {v_infty/v_esc}=1.3 at types later thanB2. To this purpose, we have calculated wind models and mass-loss ratesfor early-type supergiants in a T_eff grid covering the range betweenT_eff = 12 500 and 40 000 K. These models show the existence of a jumpin mass loss around T_eff = 25 000 K for normal supergiants, with dot{M} increasing by about a factor five from T_eff =~ 27 500 to 22 500 Kfor constant luminosity. The wind efficiency number eta=Mȯ {v_infty} / (L_*/c) also increases drastically by afactor of 2 - 3 near that temperature. We argue that the jump in massloss is accompanied by a decrease of the ratio {v_infty/v_esc}, which isthe observed bi-stability jump in terminal velocity. Usingself-consistent models for two values of T_eff, we have derived{v_infty/v_esc} = 2.4 for T_eff = 30 000 K and {v_infty/v_esc} = 1.2 forT_eff = 17 500 K. This is within 10 percent of the observed valuesaround the jump. Up to now, a theoretical explanation of the observedbi-stability jump was not yet provided by radiation driven wind theory.To understand the origin of the bi-stability jump, we have investigatedthe line acceleration for models around the jump in detail. These modelsdemonstrate that Mȯ increases around the bi-stabilityjump due to an increase in the line acceleration of Fe iii below thesonic point. This shows that the mass-loss rate of B-type supergiants isvery sensitive to the abundance and the ionization balance of iron.Furthermore, we show that the elements C, N and O are important linedrivers in the supersonic part of the wind. The subsonic part of thewind is dominated by the line acceleration due to Fe. Therefore,CNO-processing is expected not to have a large impact on dot {M},but itmight have impact on the terminal velocities. Finally, we discuss thepossible role of the bi-stability jump on the mass loss during typicalvariations of Luminous Blue Variable stars.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
| UV Spectral Classification of O and B Stars in the Small Magellanic =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1951N&db_key=AST
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| Wind variability of B supergiants. II. The two-component stellar wind of γ Arae.
The stellar wind of the rapidly rotating early-B supergiant, γAra, is studied using time series, high-resolution IUE spectroscopysecured over ~6 days in 1993 March. Results are presented based on ananalysis of several line species, including N V, C IV, Si IV, Si III, CII, and Al III. Comparisons of the time-averaged wind line morphology ofγ Ara to the UV spectra of other OB stars, and to profiles fromspherically symmetric wind models, suggest that the wind of γ Arais equatorially enhanced. Co-existing time variable features areidentified at low-velocity (redward of ~750km/s) and at higher-speedsextending to ~-1500km/s. The observed interface between these structuresis `defined' by the appearance of a discrete absorption component whichis extremely sharp (in velocity space). The central velocity of this`Super DAC' changes only gradually, over several days, between ~-400 and-750km/s in most of the ions. However, its location is shifted redwardby almost 400km/s in Al III and C II, indicating that the physicalstructure giving rise to this feature has a substantial velocity andionization jump. Constraints on the relative ionization properties ofthe wind structures are discussed. The overall wind activity in γAra exhibits a clear ion dependence, such that low-speed features arepromoted in low-ionization species, including Al III, C II, and Si III.We also highlight that - in contrast to most OB stars - there aresubstantial differences in the epoch-to-epoch time-averaged windprofiles of γ Ara and that the high-speed component observedduring our 1993 time series is normally not present. We discuss thepotential roles of the radiative bi-stability mechanism and windcompressed regions due to rapid stellar rotation for providing grosswind distortions in γ Ara.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&db_key=AST
| Absolute Magnitude-beta Calibration for OB Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2252R&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.
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Ultraviolet and optical spectroscopy of a B supergiant star in M 31
We present and discuss the UV spectrum of the supergiant star inNGC206-277 in M 31, obtained with the Faint Object Spectrograph (FOS) onHubble Space Telescope (HST). An optical blue spectrum taken at KittPeak National Observatory (KPNO) is also shown. From the optical and UVline spectra we classify the star B1.5Ia. We fit the continuum far-UVflux distribution, deriving Teff = 20,000 K, and with thistemperature we find log g = 2.5 by comparing the Hgamma lineand He I lines with predictions from Non-Local Thermodynamic Equilibrium(NLTE) models. We analyze the stellar UV wind line profiles with the SEImethod and derive a terminal velocity of upsiloninfinityapproximately equal to 700 km/s. We fit the Halpha emissionline obtained at the WHT with a newly developed (by H.J.G.L.M.L.) codesimilar to the SEI method for UV lines, and derive dm/dt = 1.3 +/- 0.510-6 solar mass/yr. We find that the P Cygni profiles of theM 31 star have slightly weaker and narrower absorptions, and no emissioncomponent. We correct our previously published mass-loss estimate for anO star (NGC206-231) in the same association. The correct value is dm/dtapproximately equals 10-6 solar mass/yr, assuming solarabundances.
| MK spectral types for OB(+) stars in the southern Milky Way
MK spectral types are presented for 291 stars selected from theCase-Hamburg Luminous Star survey.
| UBV photometry of OB+ stars in the southern Milky Way
One thousand two hundred and twenty six new observations are combinedwith previously published results of the author to yield an internalyconsistent set of magnitudes and colors on the international UBV systemfor 666 stars classified as OB+ in the Stephenson-Sanduleak OB starsurvey. The U - B, B - V diagram indicates that these stars consistprimarily of O-type stars and early B-type supergiants, reddened by upto E(B - V) = 2.1 mag.
| Carbon and nitrogen abundances in the BN supergiant HD 93840, and their implications for normal Galactic supergiants
It is demonstrated how carbon and nitrogen abundances of luminous Bstars can be determined by a combined analysis of their UV photosphericand wind lines. It is shown that HD 93840 has nearly the sametemperature and surface gravity as the normal B1 Ib star Zeta Per. Thesetwo stars are compared on the basis of their UV photospheric siliconspectra and the differences in their photospheric CNO and metallic linesare discussed. A quantitative comparison between the wind profiles ofthe two stars is made. A simple model for the compositions of bothatmospheres is used to derive the fraction of material in eachatmosphere which has undergone CNO processing. It is argued that theenriched material must have resided in a nuclear burning core for only avery short time. Best estimates of 0.09 + or - 0.07 and 0.90 + or - 0.1are made for the carbon abundances relative to cosmic ones for HD 93840and Zeta Per, respectively.
| Contemporary optical spectral classification of the OB stars - A digital atlas
Some recent developments in the optical classification of OB spectra arereviewed in terms of a comprehensive atlas of new blue-violet digitaldata from the CTIO 1-meter photon-counting system. These developmentsinclude the O3 spectral type; luminosity criteria for the O stars;OBN/OBC anomalies; and refined, interpolated late-O/early-B types.Examples of these phenomena are included among extensive spectral- andluminosity-class sequences, comprising 75 standard objects arranged into27 montages and covering the wavelength range 3950-4750 A for typesO3-B3 (-B8 at Ia). It is intended that this atlas serve a referencefunction analogous to that of the printed MK atlases, for morphologicalinvestigations of OB spectra based on digital data, which will supersedephotographic techniques in most future applications.
| Photospheric Absorption Lines in the Ultraviolet Spectra of O-Stars and B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..392P&db_key=AST
| Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars
It is argued that easily measured, reliable estimates of terminalvelocities for early-type stars are provided by the central velocityasymptotically approached by narrow absorption features and by theviolet limit of zero residual intensity in saturated P Cygni profiles.These estimators are used to determine terminal velocities, v(infinity),for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OBstars, the values are typically 15-20 percent smaller than the extremeviolet edge velocities, v(edge), while for WR stars v(infinity) = 0.76v(edge) on average. New mass-loss rates for WR stars which are thermalradio emitters are given, taking into account the new terminalvelocities and recent revisions to estimates of distances and to themean nuclear mass per electron. The relationships between v(infinity),the surface escape velocities, and effective temperatures are examined.
| Observations of Sk-69 deg 203 and the interstellar extinction towards SN 1987A
Optical and UV spectroscopic observations of the Large Magellanic Cloud(LMC) star Sk-69 deg 203 are discussed. The optical data reveal Sk-69deg 203 to be a BO.7 Ia supergiant with a moderate nitrogen enhancement,and its UV spectrum is consistent with this classification. UVinterstellar extinction curves were constructed for the star using, asflux standards, two lightly reddened LMS supergiants, which bracketSk-69 deg 203's spectral type. The resultant extinction curves areconsistent with the extinction law derived previously for the 30 Doradusregion, and the results for Sk-69 deg 203 suggest that the general 30Doradus extinction law is appropriate for dereddening the observedfluxes of SN 1987A. Published H I 21 observations place SN 1987A in aregion with a strong E-W gradient in the total hydrogen content.Comparison with the H I column density implied by the reddeningindicates that the supernova is imbedded approximately in the middle ofthe main H I complex.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Légy |
| Rektaszcenzió: | 12h38m52.50s |
| Deklináció: | -67°11'35.0" |
| Vizuális fényesség: | 6.25 |
| Távolság: | 33333.333 parszek |
| RA sajátmozgás: | -4.7 |
| Dec sajátmozgás: | -1.1 |
| B-T magnitude: | 6.268 |
| V-T magnitude: | 6.264 |
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