A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
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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.
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The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/523
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Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
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Wind variability of B supergiants. IV. A survey of IUE time-series data of 11 B0 to B3 stars
We present the most suitable data sets available in the InternationalUltraviolet Explorer (IUE) archive for the study of time-dependentstellar winds in early B supergiants. The UV line profile variability in11 B0 to B3 stars is analysed, compared and discussed, based on 16separate data sets comprising over 600 homogeneously reducedhigh-resolution spectrograms. The targets include ``normal'' stars withmoderate rotation rates and examples of rapid rotators. A gallery ofgrey-scale images (dynamic spectra) is presented, which demonstrates therichness and range of wind variability and highlights differentstructures in the winds of these stars. This work emphasises thesuitability of B supergiants for wind studies, under-pinned by the factthat they exhibit unsaturated wind lines for a wide range of ionization.The wind activity of B supergiants is substantial and has highly variedcharacteristics. The variability evident in individual stars isclassified and described in terms of discrete absorption components,spontaneous absorption, bowed structures, recurrence, and ionizationvariability and stratification. Similar structures can occur in stars ofdifferent fundamental parameters, but also different structures mayoccur in the same star at a given epoch. We discuss the physicalphenomena that may be associated with the spectral signatures. Thediversity of wind patterns evident likely reflects the role of stellarrotation and viewing angle in determining the observationalcharacteristics of azimuthally extended structure rooted at the stellarsurface. In addition, SEI line-synthesis modelling of the UV wind linesis used to provide further information about the state of the winds inour program stars. Typically the range, implied by the line profilevariability, in the product of mass-loss rate and ion fraction (mdotq_i) is a factor of ~ 1.5, when integrated between 0.2 and 0.9 v_infty ;it can however be several times larger over localised velocity regions.At a given effective temperature the mean relative ion ratios can differby a factor of 5. The general excess in predicted (forward-scattered)emission in the low velocity regime is discussed in terms of structuredoutflows. Mean ion fractions are estimated over the B0 to B1 spectralclasses, and trends in the ionic ratios as a function of wind velocityare described. The low values obtained for the ion fractions of UVresonance lines may reflect the role of clumping in the wind.
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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.
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Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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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
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Carina OB2 and its surrounding ISM.
Not Available
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Repetitive structure in the stellar wind of HD 93843: a normal O-type star
We present the results from a 28-day IUE time-series campaign monitoringthe stellar wind of the O5-type giant HD 93843. The principal aim was tostudy variability in the wind of a star with a normal projected rotationvelocity. Systematic changes are identified, amidst continuousline-profile variability, in the absorption troughs of the Siiv and Nvresonance lines. The patterns observed have characteristic time-scalesof several days and are mimicked by fluctuations (of several 100 kms^-1) in the blue wings of the saturated Civ P Cygni profile. Fourieranalysis provides support for the repeatability of wind structures in HD93843 on a 7.1-d `period'. Power at this frequency is evident only atintermediate and high velocities (i.e., above ~0.3 of the terminalvelocity). The long modulation time-scale suggests that changes in thestar itself probably provide the physical source for triggering theonset of wind structure. Unfortunately the rotational, photometric,pulsational and magnetic properties of HD 93843 are too poorlyconstrained or known to permit a more detailed interpretation of the7.1-d wind modulation in terms of potential inhomogeneities at thestellar surface. Nevertheless, our study demonstrates that the incidenceof cyclic, possibly regular, stellar-wind variability is not restrictedto rapid rotators. Comparisons with other OB stars which have exhibitedrepetitive wind changes on `periods' of several days suggest that thetime-dependent UV properties of HD 93843 are more akin to those of theO4-type supergiant zeta Puppis.
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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.
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A study of the interstellar gas surrounding Carina OB2
A huge Hi cavity delimited by a large and ellipsoidal Hi feature, hasbeen found toward the stellar association Car OB2. Based on the goodagreement found between the mean radial velocity of the Hi feature (V_HI~ -27+/-5 km s(-1) ) and the radial velocity of the OB association (V_*~ -33+/-8 km s(-1) ), and the coincidence in position between thebarycentral position of the Hi feature and the optical position of CarOB2, a physical link between the neutral gas and the stellar associationis suggested. The interaction of the stellar winds of the most massivemembers of Car OB2 with its local ISM could have given rise to both theHi low emissivity region and the surrounding \HI\ shell. The \HI\ shellappears to be expanding at ~ 22 km s(-1) . The Hi feature has acounterpart in the CO emission. The size and kinematical parameters ofthe molecular gas almost mimic those of the atomic gas. Based on theevidence presented in this paper, the anomalous behavior of the Hi alongl~ 290degr , first noticed by Humphreys & Kerr (1974), would merelybe a perturbation of the Hi local to Car OB2, and would not represent aphenomenon on a galactic scale.
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Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
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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
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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.
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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
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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.
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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.
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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.
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Ubvy-Beta Photometry of 100 Stars in the Region of Eta-Carinae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..857S&db_key=AST
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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.
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Stromgren and H-Beta Photometry of OB Associations and Open Clusters - Part Two - TRIANGULUM:16 and CARINA:OB2
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.261..847K&db_key=AST
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The chemical composition of B-supergiant atmospheres
Not Available
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A possible outburst of V430 Carinae.
Not Available
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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
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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.
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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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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.
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INHABITED SKY
