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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.
| 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.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| 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.
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| The early type contact binary system V 382 Cygni
New photometric data set of the early type contact binary V 382 Cyg havebeen analyzed with emphasis on determining the photometric mass ratio ofthe system. The result (q=0.68) supports the value given by \cite[Popper& Hill (1991).]{pop91} A study of the system using new data shows aperiod increase of about 3.28 s per century, which corresponds to a verylarge rate ~ 5.0 10(-6) {M_sun/yr} of mass transfer from the lessmassive to the more massive component under the conservative masstransfer hypothesis.
| 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.
| 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.
| Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Proper motions measured by Hipparcos confirm the large anomalousvelocities of the OB associations located around the Cygnus Superbubble(Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organizedexpanding pattern in Canis Major OB1. At the distances of theseassociations, the organized velocity patterns imply LSR velocities of upto ~ 60 km s(-1) for the associations in Cygnus, and about ~ 15 km s(-1)in Canis Major OB1. The magnitude and spatial arrangement of theexpanding motions suggests that very energetic phenomena are responsiblefor the formation of the present OB associations. This is independentlysupported by observations of the associated interstellar medium carriedout in other wavelengths. The gravitational instability scenarioproposed by Comeron & Torra 1994 (ApJ 423, 652) to account for theformation of the stars in the Cygnus Superbubble region is reviewed inthe light of the new kinematic data. It is found that the energeticrequirements set by the highest velocities on the OB associationpowering the Superbubble, Cygnus OB2, are too large by orders ofmagnitude. However, the scenario can still account for the formation ofmost of the stars if, as can be reasonably expected, the stars with thehighest measured velocities are actually runaways from Cygnus OB2itself. As for Canis Major OB1, we consider their formation in asupernova remnant, as suggested by Herbst & Assousa 1977 (ApJ, 217,473). The detection of a new runaway star, HIC 35707 (=HD 57682), whosemotion is directed away from the derived center of expansion, supportsthis scenario and provides an independent age for the supernova remnant,assuming that the runaway star was the binary companion of thesupernova. Based on a number of arguments, however, we find it unlikelythat the stars are a direct consequence of instabilities in theexpanding shell. We propose instead that their formation was triggeredin preexisting clouds, accelerated and compressed by the supernovaexplosion.
| Flux Distributions for 59 Stars in Cygnus
Absolute flux distributions are given for 59 Cygnus stars in thespectral range of 320--720 nm with a step of 5 nm. Their rms errors areon the average 2--4%. The synthetic color indices calculated for theflux distributions are compared with the observed color indices in threephotometric systems.
| UV Spectral Classification of O and B Stars in the Small Magellanic =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1951N&db_key=AST
| A Survey for H alpha Emission in Massive Binaries: The Search for Colliding Wind Candidates
I report the results of the first all-sky survey of H alpha emission inthe spectra of O-type binaries. The survey includes 26 systems, of which10 have emission that extends clearly above the continuum. This is thefirst report of emission for four of these. An additional three systemsshow small distortions in the H alpha profile that may result from weakemission. I compare the distribution of emission systems in H-R diagramsfor both binary and single stars, using a survey of single O-type starsdone by Conti (1974). Emission in main-sequence systems is extremelyrare and is completely absent in my sample of binary stars. Among binarystars, 78% of the systems containing giants show some emission, while nosingle giants in Conti's sample do. In the case of supergiants, 78% ofsingle stars show emission, while all supergiant binaries show strongemission. H alpha emission may come from a variety sources, but the factthat binaries have a higher incidence and strength of emission inpost--main-sequence stages may indicate that wind interactions are acommon source of emission in massive binaries. To ascertain whether ornot colliding winds have been observed, it will be necessary to studythe H alpha line profile throughout several orbits of each candidatecolliding wind system and look for recurring orbital-phase--relatedvariations. Such a study is underway.
| 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.
| 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
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| An 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.
| An IUE survey of interstellar H I LY alpha absorption. 2: Interpretations
We present an analysis of interstellar neutral hydrogen column densitiesobtained from archival Ly alpha absorption line data toward the completesample of B2 and hotter stars observed at high spectral resolution withthe IUE satellite. The full sample includes 554 stars and more thandoubles the number of lines of sight previously observed. Many of the B2and B1.5 stars exhibit contamination from stellar Ly alpha absorption,and were excluded from the subsequent analysis. The final working sampleincludes 393 stars. We present statistical averages for a number ofquantities derived for the sample. The stars range in distance from 0.12to 11 kpc with an average distance of 2.1 kpc. Values for averagesight-line density range from 0.017 to 8.62 atoms cm-3, withan overall average of 0.23 atoms cm-3. Neutral hydrogen anddust are well correlated, with N(H I)/E(B - V) = 4.93 x 1021cm-2 mag-1, and N(H I)/E(Bump) = 2.17 x1021 cm-2 mag-1. There is an increasein the H I to dust ratios for the densest sight lines. Evidently, the HI to dust ratios in dense clouds are higher than in the lower densitymedium between the clouds and in interarm directions. The effect isprobably an indication of dust modification in the dense clouds. The H Ito dust ratios are approx. 17% smaller for the sight lines to O starscompared to the ratios found toward B stars. We have identified sightlines with anomalously large and small values of N(H I)/E(B - V) and H(HI)/E(Bump). Some of these sight lines are well-known examples ofpeculiar extinction (i.e., HD 147933 and HD 37061 (NU Ori)). Others areless well known and may provide important new examples of regions withhighly modified dust. The number of stars with anomalously low H I todust ratios is disproportionately larger than the number of stars withanomalously high H I to dust ratios. The distribution of the gas awayform the Galactic plane for the sample of objects is complex. For thesubset of 375 stars whose lines of sight have a statistically lowprobablility of intersecting a large cloud, the distribution may beroughly approximated by an exponential density distribution, with amidplane density of 0.366 atoms cm-3, a scale height of 195pc, and a random logarithmic scattering parameter sigma p of0.159 dex.
| 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
| The violent interstellar environment around the Wolf-Rayet star HD 192163
IRAS Skyflux IR images, high-dispersion IUE UV spectra, optical spectra,and optical interference filter images are used to investigate thenature of the interstellar environment around the Wolf-Rayet star HD192163. IRAS images show an apparent 1.5 x 1.8 deg IR emission shellvery nearly centered on HD 192163, which is designated G75.5+2.4. It issuggested that this shell is a possible unrecognized SNR with anestimated age of not less than 100,000 yr if at the assumed 1.8-kpcdistance of HD 192163. A well-defined 2 x 4.5 deg region of weak IRemission lying to the southeast of HD 192163 appears to be the IRsignature of the Cyg OB1 superbubble. Analysis of IUE spectra shows thathigh-velocity components of UV interstellar absorption lines are presentfor both high and low ionization lines in 18 of 22 stars located in theCyg OB1/OB3 direction with a velocity range of +/- 90 km/s. A possibleevolutionary history for this region is outlined.
| Groups of stars with common motion in the Galaxy. Groups of O and B stars
Not Available
| An IUE and optical study of interstellar gas towards stars within the Cygnus OB1 and OB3 associations
The interstellar absorption lines formed towards 13 members of the CygOB1 and OB3 associations were examined in detail using IUE and opticalspectra. Low (0 to +17 km/s), intermediate (-24 km/s), and high (-40 to-70 km/s) velocity components were detected toward most of the stars. Itis found that the main component of the highly ionized species at +17km/s can be identified with a large-scale H II region and theintermediate-velocity component may arise in the Cyg I shell surroundingCyg OB1. It is suggested that the high-velocity components are formed ina supershell (approximately greater than 70 x 100 pc) surrounding theCyg OB1 association. It is also found that, from energy considerations,the supershell could easily have been produced by a supernova and/or thecombined effects of stellar winds.
| Tomographic separation of composite spectra - The components of the O-star spectroscopic binary AO Cassiopeiae
The UV photospheric lines of the short-period, double-lined O-starspectroscopic binary AO Cas are analyzed. Archival data from IUE (16spectra uniformly distributed in orbital phase) were analyzed with atomography algorithm to produce the separate spectra of the two stars insix spectral regions. The spectral classifications of the primary andsecondary, O9.5 III and O8 V, respectively, were estimated through acomparison of UV line ratios with those in spectral standard stars. Anintensity ratio of 0.5-0.7 (primary brighter) at 1600 A is compatiblewith the data.
| Photospheric Absorption Lines in the Ultraviolet Spectra of O-Stars and B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..392P&db_key=AST
| Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars
It is argued that easily measured, reliable estimates of terminalvelocities for early-type stars are provided by the central velocityasymptotically approached by narrow absorption features and by theviolet limit of zero residual intensity in saturated P Cygni profiles.These estimators are used to determine terminal velocities, v(infinity),for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OBstars, the values are typically 15-20 percent smaller than the extremeviolet edge velocities, v(edge), while for WR stars v(infinity) = 0.76v(edge) on average. New mass-loss rates for WR stars which are thermalradio emitters are given, taking into account the new terminalvelocities and recent revisions to estimates of distances and to themean nuclear mass per electron. The relationships between v(infinity),the surface escape velocities, and effective temperatures are examined.
| ICCD speckle observations of binary stars. V - Measurements during 1988-1989 from the Kitt Peak and the Cerro Tololo 4 M telescopes
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..965M&db_key=AST
| The upper main sequence of OB associations. II - The single-lined O stars: Spectral classification of northern stars and lines of C and N
The properties of the stars close to the upper main sequence of OBassociations are studied in order to provide constraints on the theoryof evolution of massive stars. The spectral classification of northernsingle-lined O stars, most of them belonging to the associations CygOB1, Per OB1 and Cas OB6, is presented. The classification is performedaccording to Conti's classification scheme for O stars, amended byMathys (1988). The behavior of the C and N lines of the stars isstudied, in order to determine whether CNO-processed material is visibleat their surface. Three new ON stars have been discovered: BD + 36 deg4063 (O9.71), HD 13268 (O8V), and HD 110360 (O7V).
| Stellar wind velocities and luminosities of O stars
Stellar wind velocities (v-edge not greater than v-infinity) for 110 Ostars are calculated. The spectral types in the sample range from O3through B0; all luminosity classes are represented. Stars from clustersand associations (extreme Population I) as well as field stars areconsidered. There is a weak evidence of higher v-edge for extremePopulation I stars with respect to field stars. A lower limit forstellar luminosity is also computed, and a fair positive correlationbetween this quantity and v-edge is found. Evidence is found of avariation of the ratio v-infinity/v-esc within the sample.
| X-ray emission from O-type stars - Parameters which affect it
As a result of previous analyses of the X-ray fluxes of O-type stars, ithas been established that, surprisingly, there is no correlation betweenX-ray flux and such basic parameters as M, R, v(rot), T(eff), massaccretion rate v(infinity), L(w) = mass accretion rate v(infinity), andwind energy. In this paper, other factors influencing the X-ray flux ofthe hottest stars are sought. As a result of the present analysis, it isfound that stars embedded in dense clouds are often X-ray brighter,runaway stars are fainter in X-rays, massive binaries emit more X-raysthan single stars, and radio-bright stars are also more active inX-rays. All these correlations lead to the conclusion that the stellarenvironment and the interaction of the stellar wind with circumstellarmatter (possible remnants of protostellar clouds) play a dominant rolein the production of the X-ray flux.
| 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.
| 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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Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 20h18m51.71s |
| Declinazione: | +38°16'46.5" |
| Magnitudine apparente: | 7.269 |
| Distanza: | 813.008 parsec |
| Moto proprio RA: | -5.3 |
| Moto proprio Dec: | -4.3 |
| B-T magnitude: | 7.655 |
| V-T magnitude: | 7.301 |
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