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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.
| Physical parameters and wind properties of galactic early B supergiants
We present optical studies of the physical and wind properties, plus CNOchemical abundances, of 25 O9.5-B3 Galactic supergiants. We employnon-LTE, line blanketed, extended model atmospheres, which provide amodest downward revision in the effective temperature scale of early Bsupergiants of up to 1-2 kK relative to previous non-blanketed results.The so-called "bistability jump" at B1 (Teff 21 kK)from Lamers et al. is rather a more gradual trend (with large scatter)from v&infy;/vesc3.4 for B0-0.5 supergiantsabove 24 kK to v&infy;/vesc 2.5 for B0.7-1supergiants with 20 kK ≤ Teff ≤ 24 kK, andv&infy;/vesc 1.9 for B1.5-3 supergiants below20 kK. This, in part, explains the break in observed UV spectralcharacteristics between B0.5 and B0.7 subtypes as discussed by Walbornet al. We compare derived (homogeneous) wind densities with recentresults for Magellanic Cloud B supergiants and generally confirmtheoretical expectations for stronger winds amongst Galacticsupergiants. However, winds are substantially weaker than predictionsfrom current radiatively driven wind theory, especially at mid-Bsubtypes, a problem which is exacerbated if winds are already clumped inthe Hα line forming region. In general, CNO elemental abundancesreveal strongly processed material at the surface of Galactic Bsupergiants, with mean N/C and N/O abundances 10 and 5 times higher thanthe Solar value, respectively, with HD 2905 (BC0.7 Ia) indicating thelowest degree of processing in our sample, and HD 152236 (B1.5Ia+) the highest.
| A Medium Resolution Near-Infrared Spectral Atlas of O and Early-B Stars
We present intermediate-resolution (R~8000-12,000) high signal-to-noise(S/N) H- and K-band spectroscopy of a sample of 37 optically visiblestars, ranging in spectral type from O3 to B3 and representing mostluminosity classes. Spectra of this quality can be used to constrain thetemperature, luminosity, and general wind properties of OB stars, whenused in conjunction with sophisticated atmospheric model codes. Mostimportant is the need for moderately high resolutions (R>=5000) andvery high signal-to-noise (S/N>=150) spectra for a meaningful profileanalysis. When using near-infrared spectra for a classification system,moderately high signal-to-noise (S/N~100) is still required, though theresolution can be relaxed to just a thousand or two. In the Appendix weprovide a set of very high-quality near-infrared spectra of Brackettlines in six early-A dwarfs. These can be used to aid in the modelingand removal of such lines when early-A dwarfs are used for telluricspectroscopic standards.
| 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.
| The Ultraviolet and Optical Spectra of Luminous B-Type Stars in the Small Magellanic Cloud
We present ultraviolet spectra from the Space Telescope ImagingSpectrograph (STIS) of 12 early B-type stars in the Small MagellanicCloud (SMC), composed of nine supergiants and three giants. Amorphological comparison with Galactic analogs is made using archivaldata from the International Ultraviolet Explorer (IUE). In general, theintensity of the P Cygni emission in the UV resonance lines is greaterand is seen to later spectral types in the Galactic spectra than intheir metal-deficient SMC counterparts. We attribute these effects asmost likely arising from weaker stellar winds in the SMC targets, aspredicted by radiatively driven wind theory. We also include unpublishedSTIS observations of two late O-type stars in the SMC. In combinationwith published O-type STIS data, we now have an extensive ultravioletspectral library of metal-deficient stars to use in the study ofunresolved starbursts and high-redshift star-forming galaxies. In thiscontext, we present empirical measurements for the B-type spectra of thenew ``1978 index'' suggested by Rix et al. as a probe of metallicity insuch systems.
| Terminal Velocities of Luminous, Early-Type Stars in the Small Magellanic Cloud
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS)are used to determine terminal velocities for 11 O and B-type giants andsupergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IVresonance lines. Using archival data from observations with the GoddardHigh-Resolution Spectrograph and the International Ultraviolet Explorertelescope, terminal velocities are obtained for a further five B-typesupergiants. We discuss the metallicity dependence of stellar terminalvelocities for supergiants, finding no evidence for a significantscaling between Galactic and SMC metallicities forTeff<30,000 K, consistent with the predictions ofradiation-driven wind theory. A comparison of thev&infy;/vesc ratio between the SMC and Galacticsamples, while consistent with the above statement, emphasizes that theuncertainties in the distances to galactic OB-type stars are a seriousobstacle to a detailed comparison with theory. For the SMC sample thereis considerable scatter in v&infy;/vesc at agiven effective temperature, perhaps indicative of uncertainties instellar masses.
| 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.
| Space Telescope Imaging Spectrograph Ultraviolet Spectroscopy of Early B Supergiants in M31
We analyze Space Telescope Imaging Spectrograph (STIS) spectra in the1150-1700 Å wavelength range obtained for six early B supergiantsin the neighboring galaxy M31. Because of their likely high (nearlysolar) abundance, these stars were originally chosen to be directlycomparable to their Galactic counterparts and represent a much neededaddition to our current sample of B-type supergiants, in our efforts tostudy the dependence of the wind momentum-luminosity relationship onspectral type and metallicity. As a first step to determine wind momentawe fit the P Cygni profiles of the resonance lines of N V, Si IV, and CIV with standard methods and derive terminal velocities for all of theSTIS targets. From these lines we also derive ionic stellar wind columndensities. Our results are compared with those obtained previously inGalactic supergiants and confirm earlier claims of ``normal'' wind lineintensities and terminal velocities in M31. For one-half of the samplewe find evidence for an enhanced maximum turbulent velocity whencompared to Galactic counterparts. Based on observations with theNASA/ESA Hubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555.
| The Spectrum of the Mass Donor Star in SS 433
We present results from a short series of blue, moderate-resolutionspectra of the microquasar binary SS 433. The observations were made ata time optimized to find the spectrum of the donor star, i.e., when thedonor was in the foreground and well above the plane of the obscuringdisk. In addition to the well-known stationary and jet emission lines,we find evidence of a weak absorption spectrum that resembles that of anA-type evolved star. These lines display radial velocity shifts oppositeto those associated with the disk surrounding the compact star, and theyappear strongest when the disk is maximally eclipsed. All theseproperties suggest that these absorption lines form in the atmosphere ofthe hitherto unseen mass donor star in SS 433. The radial velocityshifts observed are consistent with a mass ratioMX/MO=0.57+/-0.11 and masses ofMO=19+/-7 Msolar and MX=11+/-5Msolar. These results indicate that the system consists of anevolved, massive donor and a black hole mass gainer.
| An analysis of STIS HST UV spectra of M 33 early B supergiants
We present terminal velocities of M 33 B-supergiants, obtained from STISHST spectra as part of our programme to investigate the Wind Momentum -Luminosity Relationship (WLR) in the Local Group. Terminal velocitiesare derived from their N V, C Iv, and Si Iv resonance lines in UVspectra. Comparing with IUE spectra of Galactic B-supergiants we foundevidence of low metallicity in three of our objects. The terminalvelocities are consistent with the corresponding values of Galacticstars, except for B-133. For this star we find a very largevinfty and a red Si Iv component deeper than the blue one,that might be an indication of binarity. The average ratio betweenterminal and turbulent wind velocities is 0.25, well above the valuefound for Galactic stars. Partly based on INES data from the IUEsatellite.
| B Stars as a Diagnostic of Star Formation at Low and High Redshift
We have extended the evolutionary synthesis models by Leitherer et al.by including a new library of B stars generated from the IUEhigh-dispersion spectra archive. We present the library and show how thestellar spectral properties vary according to luminosity classes andspectral types. We have generated synthetic UV spectra for prototypicalyoung stellar populations varying the IMF and the star formation law.Clear signs of age effects are seen in all models. The contribution of Bstars in the UV line spectrum is clearly detected, in particular forgreater ages when O stars have evolved. With the addition of the newlibrary we are able to investigate the fraction of stellar andinterstellar contributions and the variation in the spectral shapes ofintense lines. We have used our models to date the spectrum of the localsuper-star cluster NGC 1705-1. Photospheric lines of C III λ1247,Si III λ1417, and S V λ1502 were used as diagnostics todate the burst of NGC 1705-1 at 10 Myr. Interstellar lines are clearlyseen in the NGC 1705-1 spectrum. Broadening and blueshifts of severalresonance lines are stronger in the galaxy spectrum than in our modelsand are confirmed to be intrinsic of the galaxy. Si II λ1261 andAl II λ1671 were found to be pure interstellar lines with anaverage blueshift of 78 km s-1 owing to a directed outflow ofthe interstellar medium. We have selected the star-forming galaxy1512-cB58 as a first application of the new models to high-z galaxies.This galaxy is at z=2.723, it is gravitationally lensed, and its highsignal-to-noise ratio Keck spectrum shows features typical of localstarburst galaxies, such as NGC 1705-1. Models with continuous starformation were found to be more adequate for 1512-cB58 since there arespectral features typical of a composite stellar population of O and Bstars. A model with Z=0.4 Zsolar and an IMF with α=2.8reproduces the stellar features of the 1512-cB58 spectrum.
| Hot massive stars in Local Group galaxies.
Not Available
| 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
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. I. Canis Major - Puppis - Vela
Strömgren and Hβ photometry of OB-stars generally brighterthan 9.5 mag in the Canis Major - Puppis - Vela region of Milky Way isreported. The observations are based on the Milky Way luminous-star (LS)identifications and are designed to create a complete, magnitude-limitedsample of LS for this field. We present new uvby photometry for 127 LSand Hβ photometry for 25 of them. These observations are part of anongoing effort to improve the completeness of the existing uvbybetadata-base for the bright OB-type stars in the Milky Way, with the aim toinvestigate the structure of selected star-forming regions. Based ondata from the Strömgren Automatic Telescope of the CopenhagenAstronomical Observatory, La Silla. Tables 3 and 4 are only available inelectronic form at the CDS via anonymous ftp to 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&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.
| 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.
| Far-ultraviolet stellar photometry: Fields in Sagittarius and Scorpius
Far-ultraviolet photometry for 741 objects in a field in Sagittariuscentered near M8 and 541 objects in a field centered near sigma Scorpiiis presented. These data were extracted from electographic imagesobtained with two cameras during a shuttle flight in 1991 April/May. Thecameras provided band passes with lambdaeff = 1375 A andlambdaeff = 1781 A. Synthetic colors show that these bandsare sensitive to effective temperature for hot stars. Our measurementswere placed on a quantitative far-ultraviolet magnitude scale byconvolving the spectra of stars observed by IUE with our cameras'spectral response functions. Fifty-eight percent of the ultravioletobjects were identified with visible stars using the SIMBAD databasewhile another 40% of the objects are blends of early type stars tooclose together to separate with our resolution. Our photometry iscompared with that from the TD-1, OAO 2, and ANS satellites and the S201(Apollo 16) far-ultraviolet camera and found to agree at the level of afew tenths of a magnitude. Unlike previous studies, almost half of theidentified visual counterparts to the ultraviolet objects are early Bstars. A plot of distance modulus against ultraviolet color excessreveals a significant population of stars with strong ultravioletexcess.
| 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.
| Ultraviolet FeIII lines in the spectra of high galactic latitude early-type stars
Using high resolution spectral data from the International UltravioletExplorer satellite, we present qualitative and quantitative comparisonsof blends of Fe III absorption lines in the region1890A<=λ<=1930A for a sample of fifteen high latitudeB-type and standard stars. Standard and halo stars were matched ineffective temperature and surface gravity using Stroemgren [c_1_] andHβ photometry, and LTE model atmosphere codes were used toinvestigate whether they had similar iron abundances. We conclude thatwhile most of the halo stars have Population I iron abundances and maybe young objects, one star, HD 177566, has significant iron and silicondepletions and is most probably an old, evolved star. In view of thecoincidence of the atmospheric parameters of this star with those ofyoung B-type stars, we consider a post-AGB evolutionary status to belikely for HD 177566.
| Groups of stars with common motion in the Galaxy. Groups of O and B stars
Not Available
| Photospheric velocity gradients in B1 supergiants
We present IUE spectra for a set of B1 supergiants. These data clearlydemonstrate that the Si III 1300A multiplet (lower level 6.6 ev aboveground) becomes progressively more asymmetric with increasing luminosityor, equivalently, mass loss. In the most luminous supergiants, the coresof the 1300A multiplets become displaced by up to -150 km/s relative tonearby, weaker lines. In addition, systematic velocity shifts andasymmetries are also present in the strong Si III singlets 1312A and1417A in the more luminous stars. The obvious implication of theseobservations is that the outer photospheres of B supergiants areaffected by radial expansion, and this may account for why even non-LTEline analyses of these stars require large micro-turbulent velocityfields, and why line blanketed LTE models underestimate their overall UVline blanketing.
| 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.
| Massa's star, HD 93840 - A new extreme BN supergiant
New optical digital spectrograms of HD 93840 and several comparisonobjects are presented and discussed, together with IUE high-resolutiondata for the same stars. The optical observations confirm HD 93840 (BN1Ib) as an extreme nitrogen-enhanced supergiant, as originally suggestedby Massa (1989). The contrasts with HD 96248 (BC1.5 Iab) are especiallystriking. The rich UV stellar-wind phenomenology of these objects isdiscussed in some detail. The spectroscopic characteristics andintermediate galactic latitude of HD 93840 suggest a relationship to RhoLeo, and perhaps to HD 105056.
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