On the origin of field O-type stars
Aims. We aim to identify the origins of field O-stars in the nearest 2to 3 kpc around the Sun using the best presently available kinematicdata on O-stars and on young open clusters. We investigate the questionof whether the present-day data are consistent with the assumption thatO-stars have formed in groups (clusters, associations), or in isolation. Methods: We apply the epicycle theory to back-trace the orbits ofO-type stars and of candidate parent open clusters. Results: From the370 O-stars in the “Galactic O star catalog v 2.0” (GOSV2)we have investigated 93 stars classified as field, and found the originfor 73 of them in 48 open clusters younger than 30 Myr. Only for 32stars or about 9% of all O-stars from this catalogue is the question oftheir origin in groups not solved; some of them may have originated inisolation or may have disintegrated the group in which they formed.Fifty percent of the young open clusters (age < 30 Myr) in the“Catalogue of Open Cluster Data” (COCD) have O-stars asmembers, or have ejected at least one O-star in the first 10 Myr oftheir life, or both. During this period the average mass loss from openclusters by ejecting O-stars is found to be 3 to 5 M_ȯ per Myr. Weprove that ζ Pup had its origin in the open cluster Trumpler 10which it left about 2.5 Myr ago, and that its present-day distance is300 pc (compared to 440 pc before). The revised distance implies asignificant revision of the stellar parameters (a radius of 14 R_ȯ,a mass of 22.5 M_ȯ, and a luminosity of log L/L_ȯ of 5.74)i.e., ζ Pup is closer, less massive, and less luminous thanpreviously thought. Our findings provide independent estimates of thepresent-day distances and absolute magnitudes of field O-stars.
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Adaptive Optics Photometry and Astrometry of Binary Stars. III. a Faint Companion Search of O-Star Systems
We present the results of an adaptive optics survey for faint companionsamong Galactic O-type star systems (with V lsim 8) using the AdvancedElectro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyedthese O-star systems in the I-band, typically being able to detect acompanion with a magnitude difference of utrimI lsim 6 in theprojected separation range 0farcs5 < ρ < 1farcs0, andutrimI lsim 9.5 in the range 1farcs0 < ρ < 5farcs0.In the course of the survey, we discovered 40 new companions among 31 ofthe 116 objects examined and made astrometric and differential magnitudemeasurements of 24 additional known pairs, several of them beingconfirmation detections. We present new astrometric orbits for twobinaries, BU 1032AB (WDS 05387–0236 σ Ori AB) and SEE 322(WDS 17158–3344 HD 155889AB). We lack magnitude differences forother filter bands, so it is difficult to determine physical fromline-of-sight companions, but we present empirical arguments for thelimiting magnitude difference where field contamination is significant.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate.
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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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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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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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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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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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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Binarity among B-stars in NGC 6231.
We have measured radial velocities for 53 B-type stars, between B1 andB9, in the young open cluster NGC6231 through a cross-correlationtechnique with synthetic spectra. Two measurements for 36 stars of thesample were obtained with a time separation of about two years. Wederived a minimum binary fraction of 52% in the considered population.The velocity determination precisions were simulated and we analysedtheir dependence upon the S/N ratios of the spectra and upon the stellarrotational velocities. We discuss the selection of the templates for thecorrelation.
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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
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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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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.
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The Spacelab-1 Very Wide Field Survey of UV-excess objects. IV. The performance of the instrument in combination with optical photometry as a means of identifying stars with peculiar properties.
UV (195 nm) and Stroemgren uvby photometry of a 110 square degree fieldat high southern galactic latitudes are analyzed through a comparison ofi) UV magnitudes for 57 stars of various types common to the publishedTD1 catalogue and the Very Wide Field Camera (VWFC); and ii) observedand theoretical two-colour diagrams. The higher sensitivity of the VWFC(=~0.5magnitude) and its more complete survey are exemplified by thedetection and UV measurement of a series of objects with moderateUV-excess in addition to detection of some very blue objects of variousnature down to fainter than 12th magnitude in the optical domain. Adeeper survey with a VWFC-type instrument could provide a completesample for studies of the group properties of faint blue stars. Duringthe uvby reductions it was found that the usual procedure of plottingresiduals as functions of declination, hour angle and airmass can be apowerful and diagnostic test of photometer rigidity.
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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.
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A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
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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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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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Variability and mass loss in IA O-B-A supergiants
Recently completed catalogs of MK spectral types and UBV photometry of1227 OB stars in the southern Milky Way have been analyzed toinvestigate brightness and color variability among the Ia supergiants.It is found that brightness variability is common among the O9-B1supergiants with typical amplitudes about 0.1 and time scales longerthan a week and shorter than 1000 days. Among the A supergiantsfluctuations in U-B color are found on similar time scales and withamplitude about 0.1. For many early Ia supergaints there is a poorcorrelation between Balmer jump and spectral type, as had been knownpreviously. An attempt to correlate the Balmer jump deficiency with massloss rate yielded uncertain results.
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On the apparent normality of O and B stars far from the galactic plane
Results of a search for subluminosity or other peculiarities in thespectra of apparently normal OB stars located at large distances fromthe galactic plane are presented. Photographic spectrograms werecompared for stars of type B5 and earlier located within 0.5 kpc of andfurther than 1.5 kpc from the galactic plane, and for three subdwarfstars. Values of the projected axial rotation, surface gravity, absolutemagnitude and the strengths of certain He I and Balmer lines determinedfor both groups of OB stars are found to be similar, and distinct fromthe spectral characteristics of the subdwarfs. The results suggest that,unless the normality of the distant OB stars is illusory, either OBstars can be formed outside the galactic plane, or a mechanism mustexist to eject them from the plane with large velocities, unless theirmain sequence lifetimes are substantially longer than currentlybelieved.
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Infrared photometry of southern early-type stars
The paper presents infrared photometry tied to the JHKL (1.2-3.5microns) broadband photometric system for 229 southern early-type stars.To determine data for stars of low reddening intrinsic visual-IR colorindices were used; the E(V-K)/E(B-V) diagram was applied to evaluate theratio of total selective extinction. A mean value of R = 3.12 plus orminus 0.05 was found for stars close to the galactic plane, but a highervalue of R (about 4.0) applies to the Orion and Sco-Oph regions.Infrared two-color diagrams were used to investigate the occurrence ofinfrared excess emission in different classes of shell star; no excesseswere found for supergiants or Of stars. It is concluded that theanomalous position HD 164740 in the two-color diagrams is produced bystrong infrared excess and not by a peculiar extinction law.
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On the origin of intermediate-latitude OB stars
An attempt is made to trace the origin of early-type stars observed atappreciable distances from the galactic plane. Because uncertainties inthe proper motions make space motions and hence dynamical lifetimesrather inaccurate, a theory of oscillations normal to the plane has beenused to compute radial velocities for 138 intermediate-latitude OBstars. These theoretical values are then compared with the observedradial velocities, and it is found that the low-velocity stars wereprobably ejected from the plane some time after formation, while thehigh-velocity stars were ejected very soon after formation. Velocitiesof ejection perpendicular to the plane are computed and show a narrowdistribution with a mean absolute value of 7 km/s together with a spreadof velocities from about 40 to over 200 km/s. The data are in reasonableagreement with a 'sling' effect and 'runaway' origin for the stars inthe sample.
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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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Spectroscopic studies of O-type stars. VIII - Radial velocities and the K-term
Radial velocities are measured on coude spectrograms of over 200 O-typestars in both hemispheres. The selection of effective wavelengths forthe stellar lines to be measured is reviewed, and the measuredvelocities are compared with those available in a catalog of O stars.The Trumpler (1935) effect (a reported anomalous redshift in certain Ostars) is inconclusively reinvestigated, atmospheric motions in Of starsare examined, and some kinematic properties of O stars are discussedstatistically. It is found that 58% of all O stars and 41% of all the Ofstars considered are certain or probable binaries. A K-term in the rangefrom 1 to 2 km/s is derived for the O stars, but the Of stars are shownto have a highly significant negative K-term. It is suggested that thesystematically negative peculiar velocities of the Of stars are due tooutflow of material beginning at the photospheric level.
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Spectroscopic studies of O-type stars. VII. Rotational velocities V*sin(i) and evidence for macroturbulent motions.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJ...213..438C&db_key=AST
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The OBn and OBc stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..419W&db_key=AST
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INHABITED SKY
