On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
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A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
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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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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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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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ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
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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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A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
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Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&db_key=AST
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An IRAS/ISSA Survey of Bow Shocks Around Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2914V&db_key=AST
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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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Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..749R&db_key=AST
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The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
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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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High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548
The interstellar medium was studied in the direction to the WR stars HD96548 and HD 97152, and the results are reported. New observational dataon the UV spectra of several field stars near both these WR stars arepresented. The high-velocity gas seen in the spectra of these starssuggests that the detected expanding interstellar gas structure consistsof two OB cluster supershells. The presence of high-velocity absorptioncomponents in one of five field star spectra in the direction of themore isolated WR star HD 96548 suggests that this expanding gas does notoriginate from the optical ring nebula RCW 58 surrounding HD 96548, aspreviously believed, but instead indicates the detection of a previouslyunknown expanding interstellar shell in this line of sight.
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The Einstein X-ray Observatory Catalog of O-type stars
A catalog of X-ray count rates for all O-type stars surveyed by theEinstein Observatory is presented. The procedures by which the IPC andHigh Resolution Imager rates are converted to emitted X-ray luminositiesare discussed in detail. The catalog contains 289 stars with 89detections and 176 upper bounds for the observed count rates. Precisepositions for 43 O-type stars are given whose previously known locationswere unknown or erroneous. It is argued that most O-type stars are X-raypoint sources, but some are possibly embedded in extended nebulae and/orbubbles. The X-ray spectra of O-type stars are discussed briefly, and itis argued that their mean spectrum can reasonably be taken as an 0.5 keVthermal bremsstrahlung model. It is argued that at least 30 percent ofall O-type stars are variable in X-rays.
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The stellar winds of 203 Galactic O stars - A quantitative ultraviolet survey
Measurements of the resonance lines of C IV, N V, and Si IV in a sampleof 203 O stars observed using IUE in a high-resolution mode arepresented. The data are discussed using a consistent set of radius,luminosity, and mass estimates. The ratio of the maximum observedvelocity and the terminal (farfield) velocity is found to average at 3.0for 131 stars with strong or saturated lines, and at 2.6 for all stars.An expression is given which is the best available predictor of O starmass loss rates, giving an accuracy better than a factor of twoirrespective of luminosity class. The ionization fractions C(3+)/C andN(4+)/N are found to be independent of stellar effective temperature,but increase by a factor of about two from main sequence stars tosupergiants. Two new possible ON stars are identified, and enhancedsurface nitrogen abundance is confimed in ON stars. Discrete narrowabsorption features are found to be virtually universal characteristicof O star P Cygni profiles.
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Expanding shells of interstellar gas in the lines-of-sight to Wolf-Rayet stars
High-velocity interstellar gas was detected in the directions toward theWR stars HD 97152 and HD 96548 by interstellar resonance absorptionlines in high-resolution IUE spectra. Shifted line components in thespectra of 5 field stars covering an area of 2 deg around HD 97152exhibit velocities up to -150 km/sec. The presence of numerous otherearly-type stars in this region plus an analysis of IRAS image datasuggest that this expanding interstellar structure is a stellarwind-blown shell which may be unrelated to the WR star. High-velocitygas seen in the line-of-sight to HD 96548 does not originate from thestar's optical ring nebula (RCW 58) but from a large, expandinginterstellar shell at least 40 pc in diameter. With velocities up to-120 km/sec and a location well off the galactic plane, thisinterstellar gas may be a highly evolved supernova remnant like thatassociated with the WR star HD 50896.
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The kinematical and binary properties of association and field O stars
A catalog of 195 Galactic O-type stars brighter than V = 8.0 mag hasbeen compiled to compare the velocity distribution and binary frequencyamong cluster and association, field, and runaway stars. Both the fieldstars and runaway stars have a larger dispersion in peculiar radialvelocity, a more positive mean peculiar radial velocity, and a widerz-distribution than stars found in clusters and associations, which isconsistent with the ejection of field and runaway stars from theirbirthplaces in associations. Visual binaries are common among stars inclusters and associations, but their incidence is a factor of 2 loweramong field stars, and they are absent in the runaway stars. Similarly,there is a deficiency of spectroscopic binaries among field stars, andespecially the runaway stars, relative to the numbers found in clustersand associations. Many of these properties can be understood in terms ofejection through close gravitational interactions with binary starsduring an early high number density epoch in the evolution of clusters.
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X-ray properties of hot stars. I - On a dichotomy among O-type stars
X-ray data gathered by the Einstein Observatory are discussed in termsof the origins of the emissions from O type stars. The sampling islimited to a radius of about 2.5 kpc and energies of 0.2-4 keV.Bolometric (Lb) and X-ray (Lx) luminosities of 47 objects are listed.All slow stars in the sample are found to have an Lx/Lb ratio of morethan 0.00000016. Runaway stars are determined to have a smaller Lx valueand are not found in dense, bright nebulae. The data are used to set alimit of 10 to the 14th cm for the maximum size of an X-ray emittingregion. It is suggested that runaway O-type stars escape from dense,bright nebulae, where they are formed. Interstellar shocks appear whenthe interstellar medium encounters the dense nebular wind and emit theobserved X-rays.
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UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
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The initial mass function for massive stars
A machine readable catalog of over 750 galactic O stars with publishedphotometry, spectral types, and luminosity classes has been compiled.The catalog is probably complete to a distance of about 2.5 kpc. Fromthis volume-limited data, the initial mass function (IMF) for stars moremassive than 20 solar masses has been derived. This IMF differs fromthat of Miller and Scalo (1979) and of Lequeux (1979), in havingproportionately more O type stars and not as steep a fall-off in numberof stars with increasing mass. Dividing the sample into stars inside andoutside the solar circle, a substantial difference in the IMF of themost massive stars is found. There are proportionally more toward thegalactic center. This gradient in the IMF may be related to the observedspace density of Wolf-Rayet stars, which are descendants of O typestars.
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A search for expanding supershells of gas around OB associations
The results of a search for giant, rapidly expanding shells of gassurrounding OB associations are recorded. Two out of thirteen nearbyassociations (Orion and Carina) show supershells of gas with radii ofabout 100 pc, expansion velocities of about 100 km/sec, and ages ofabout 400,000 years. Observations of the newly discovered Carinasupershell are presented. It is suggested that these features are formedby supernova explosions in the associations. The birthrate ofassociation supernovae than lies between 1.5 x 10 to the -14th/cu pcper/year and 10 to the -13th/cu pc per/year.
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On the origin and distribution of C IV and SI IV ions in the neighboring interstellar medium
IUE spectrometer observational data are reported on the C IV, Si IV, andN V absorption lines in 46 distant stars at FWHM resolution of 30km/sec. A simple analytic theory is given for these contributions,including the effects of ionization by a soft X-ray background. Whilefor some of the most distant field stars a photoionized contribution maybe ruled out, C IV absorption lines are detected which are shallow andbroad. It is suggested that what are being detected in these cases arecontributions from the hot interstellar gas that is responsible for theO VI absorption lines. Most of the Si IV and C IV lines probably arisein the H II regions surrounding the observed star or its neighbors.
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On the 4430 A interstellar band - A visual classification
A system of visual classification of the strength of the interstellarband 4430 A has been developed, based on spectra taken at spectralclassification dispersion. The intensity of the band was divided into 8main classes, defined by a group of selected standard stars. The systemwas applied to 1,111 southern OB stars contained in the catalog ofspectral types by Garrison, Hiltner, and Schild (1977). The mean errorin the classification was estimated to be plus or minus 1 class.Equivalent widths were measured for 100 stars; an excellent correlationwith the visual estimations was obtained. A calibration between thesetwo parameters is given.
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Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...38..309H&db_key=AST
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MK spectral classifications for southern OB stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...35..111G&db_key=AST
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