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A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| AKARI's infrared view on nearby stars. Using AKARI infrared camera all-sky survey, 2MASS, and Hipparcos catalogs
Context. The AKARI, a Japanese infrared space mission, has performed anAll-Sky Survey in six infrared-bands from 9 to 180 ?m with higherspatial resolutions and better sensitivities than IRAS. Aims: Weinvestigate the mid-infrared (9 and 18 ?m) point source catalog (PSC)obtained with the infrared camera (IRC) onboard AKARI, in order tounderstand the infrared nature of the known objects and to identifypreviously unknown objects. Methods: Color-color diagramsand a color-magnitude diagram were plotted with the AKARI-IRC PSCand other available all-sky survey catalogs. We combined the Hipparcosastrometric catalog and the 2MASS all-sky survey catalog with theAKARI-IRC PSC. We furthermore searched literature and SIMBADastronomical database for object types, spectral types, and luminosityclasses. We identified the locations of representative stars and objectson the color-magnitude and color-color diagram schemes. Theproperties of unclassified sources can be inferred from their locationson these diagrams. Results: We found that the (B-V) vs.(V-S9W) color-color diagram is useful for identifying thestars with infrared excess emerged from circumstellar envelopes ordisks. Be stars with infrared excess are separated well from other typesof stars in this diagram. Whereas (J-L18W) vs. (S9W-L18W)diagram is a powerful tool for classifying several object types.Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars formdistinct sequences in this color-color diagram. Young stellarobjects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, andplanetary nebulae (PNe) have the largest mid-infrared color excess andcan be identified in the infrared catalog. Finally, we plot the L18W vs.(S9W-L18W) color-magnitude diagram, using the AKARI data togetherwith Hipparcos parallaxes. This diagram can be used to identify low-massYSOs and AGB stars. We found that this diagram is comparable to the [24]vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources usingthe Spitzer Space Telescope data. Our understanding of Galactic objectswill be used to interpret color-magnitude diagram of stellar populationsin the nearby galaxies that Spitzer Space Telescope observed. Conclusions: Our study of the AKARI color-color andcolor-magnitude diagrams will be used to explore properties ofunknown objects in the future. In addition, our analysis highlights afuture key project to understand stellar evolution with a circumstellarenvelope, once the forthcoming astronometrical data with GAIA areavailable.Catalog (full Tables 3 and 4) are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/514/A2
| The High Angular Resolution Multiplicity of Massive Stars
We present the results of a speckle interferometric survey of Galacticmassive stars that complements and expands upon a similar survey madeover a decade ago. The speckle observations were made with the Kitt PeakNational Observatory and Cerro Tololo Inter-American Observatory 4 mtelescopes and USNO speckle camera, and they are sensitive to thedetection of binaries in the angular separation regime between 0farcs03and 5'' with relatively bright companions (ΔV < 3). We reporton the discovery of companions to 14 OB stars. In total we resolvedcompanions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%),and 89 of 139 B-stars (64%; an enriched visual binary sample that weselected for future orbital determinations). We made a statisticalanalysis of the binary frequency among the subsample that are listed inthe Galactic O Star Catalog by compiling published data on other visualcompanions detected through adaptive optics studies and/or noted in theWashington Double Star Catalog and by collecting published informationon radial velocities and spectroscopic binaries. We find that the binaryfrequency is much higher among O-stars in clusters and associationscompared to the numbers for field and runaway O-stars, consistent withpredictions for the ejection processes for runaway stars. We present afirst orbit for the O-star δ Orionis; a linear solution of theclose, apparently optical, companion of the O-star ι Orionis; andan improved orbit of the Be star δ Scorpii. Finally, we listastrometric data for another 249 resolved and 221 unresolved targetsthat are lower mass stars that we observed for various other scienceprograms.
| Possible dark matter in spiral galaxies of the coma cluster
Not Available
| Near Infrared Spectra of Galactic Wolf-Rayet Stars
Spectra of 37 Galactic WR stars were observed and reduced in thespectral range 790--895 nm. The main spectral features are identifiedand the equivalent widths and FWHMs of the strongest emission lines aremeasured. The equivalent width of the diffuse interstellar band at 862nm is also measured and the new estimates of color excessesE(B-V) are derived by using an empirical relationship betweenthe equivalent width and the color excess. The equivalent width ratiosfor the lines C III 850 nm, C IV 886 nm and C II 880 nm were found tocorrelate well with the WC subtype.
| Radial pulsations of Wolf-Rayet stars and the problem of mass loss in them
In order to study the problem of mass loss by Wolf-Rayet stars, wecarried out numerical simulations of non-linear pulsations of theseobjects. Although our computations do not show direct dynamical massloss, qualitative estimates show that certain as yet unobservedpulsations could in principle, create conditions facilitating massoutflows from Wolf-Rayet stars.
| A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
New Technology Telescope (NTT)/Son of Isaac (SOFI) imaging andspectroscopy of the Wolf-Rayet population in the massive clusterWesterlund 1 are presented. Narrow-band near-infrared (IR) imagingtogether with follow up spectroscopy reveals four new Wolf-Rayet stars,of which three were independently identified recently by Groh et al.,bringing the confirmed Wolf-Rayet content to 24 (23 excluding source S)- representing 8 per cent of the known Galactic Wolf-Rayet population -comprising eight WC stars and 16 (15) WN stars. Revised coordinates andnear-IR photometry are presented, whilst a quantitative near-IR spectralclassification scheme for Wolf-Rayet stars is presented and applied tomembers of Westerlund 1. Late subtypes are dominant, with no subtypesearlier than WN5 or WC8 for the nitrogen and carbon sequences,respectively. A qualitative inspection of the WN stars suggests thatmost (~75 per cent) are highly H deficient. The Wolf-Rayet binaryfraction is high (>=62 per cent), on the basis of dust emission fromWC stars, in addition to a significant WN binary fraction from hardX-ray detections according to Clark et al. We exploit the large WNpopulation of Westerlund 1 to reassess its distance (~5.0kpc) andextinction (AKS ~ 0.96mag), such that it islocated at the edge of the Galactic bar, with an oxygen metallicity ~60per cent higher than Orion. The observed ratio of WR stars to red andyellow hypergiants, N(WR)/N(RSG + YHG) ~3, favours an age of~4.5-5.0Myr, with individual Wolf-Rayet stars descended from progenitorsof initial mass ~40-55Msolar. Qualitative estimates ofcurrent masses for non-dusty, H-free WR stars are presented, revealing10-18Msolar, such that ~75 per cent of the initial stellarmass has been removed via stellar winds or close binary evolution. Wepresent a revision to the cluster turn-off mass for other Milky Wayclusters in which Wolf-Rayet stars are known, based upon the latesttemperature calibration for OB stars. Finally, comparisons between theobserved WR population and subtype distribution in Westerlund 1 andinstantaneous burst evolutionary synthesis models are presented.Based on observations made with ESO telescopes at the La SillaObservatory under programme IDs 073.D-0321 and 075.D-0469.E-mail: Paul.crowther@sheffield.ac.uk
| The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
Context: .Very massive stars pass through the Wolf-Rayet (WR) stagebefore they finally explode. Details of their evolution have not yetbeen safely established, and their physics are not well understood.Their spectral analysis requires adequate model atmospheres, which havebeen developed step by step during the past decades and account in theirrecent version for line blanketing by the millions of lines from ironand iron-group elements. However, only very few WN stars have beenre-analyzed by means of line-blanketed models yet. Aims: .Thequantitative spectral analysis of a large sample of Galactic WN starswith the most advanced generation of model atmospheres should provide anempirical basis for various studies about the origin, evolution, andphysics of the Wolf-Rayet stars and their powerful winds. Methods:.We analyze a large sample of Galactic WN stars by means of the PotsdamWolf-Rayet (PoWR) model atmospheres, which account for iron lineblanketing and clumping. The results are compared with a syntheticpopulation, generated from the Geneva tracks for massive starevolution. Results: .We obtain a homogeneous set of stellar andatmospheric parameters for the Galactic WN stars, partly revisingearlier results. Conclusions: .Comparing the results of ourspectral analyses of the Galactic WN stars with the predictions of theGeneva evolutionary calculations, we conclude that there is roughqualitative agreement. However, the quantitative discrepancies are stillsevere, and there is no preference for the tracks that account for theeffects of rotation. It seems that the evolution of massive stars isstill not satisfactorily understood.
| 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.
| The neutral gas in the environs of the Wolf Rayet stars in the Circinus OB1 association
We have investigated the neutral hydrogen in the direction of theCircinus OB1 association with particular emphasis in the study of thevicinity of the WR stars WR 65 and WR 67. The HI line data were obtainedwith the Australia Telescope Compact Array with a synthesized beam of4\farcm0 × 2\farcm7 and a velocity resolution of 1.1 kms-1. These data led to the discovery of a large cavitysurrounded by an almost complete shell in agreement with the locationsand distances of the two WR stars. We propose that the HI featuresconstitute an interstellar bubble created by the powerful winds of theWR stars and their progenitors. By assuming a distance of 3 kpc, wecalculate for this HI bubble a linear radius of 22 pc, a swept-up massof 1600 M_ȯ and an expansion velocity of more than 7 kms-1. High angular resolution IRAS infrared data (HIRES)reveal the presence of a ring with good spatial correlation with the HIshell. Eight IRAS protostellar candidates located around the HI cavitysuggest that star formation may be taking place in the shell. Furtherinvestigation is required to confirm this proposition.
| Pismis 20: One or two clusters?
We present UBVRI polarimetric observations of stars in the direction ofthe open cluster Pismis 20 and WR67. It is found that the observed members segregatepolarimetrically into two groups, with different associated meanPmax (4.31 and 6.08% respectively). Although in theliterature these stars are considered as members of the same cluster,the polarized light from these groups clearly differs. There are twopossible explanations: very efficient polarizing dust particles existsbetween certain members of the cluster; or else Pismis20 is composed of different groupings superimposed along theline of sight. WR 67 belongs to the group moreaffected by the dust.Based on observations obtained at Complejo Astronómico ElLeoncito, operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the Universities of La Plata,Córdoba, and San Juan.
| 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.
| The enigmatic WR46: A binary or a pulsator in disguise. III. Interpretation
Photometric and spectroscopic monitoring campaigns of WR46 (WN3p), as presented in Veen et al. (2002a,b; hereafterPapers I and II, respectively), yield the following results. The light-and colour variations reveal a dominant single-wave period ofPsw89=0.1412 d in 1989, andPsw91 =0.1363 d in 1991. Because of a smalldifference in the minima, this periodicity may be a double-wavephenomenon (Pdw). The line fluxes vary in concert with themagnitudes. The significant difference of the periods can be either dueto the occurence of two distinct periods, or due to a gradual change ofthe periodicity. A gradual brightening of the system of 0.12m appearedto accompany the period change. In addition, the light variations in1989 show strong evidence for an additional period Px=0.2304d. Generally, the radial velocities show a cyclic variability on a timescale of the photometric double-wave. However, often they do not vary atall. The observed variability confirms the Population I WR nature of thelight source, as noted independently by Marchenko et al. (2000). In thepresent paper, we first show how the photometric double-wave variabilitycan be interpreted as a rotating ellipsoidal density distribution in thestellar wind. Subsequently, we discuss what mechanisms could drive sucha configuration. First, stellar rotation of a single star is discardedas a likely cause. Second, the obvious interpretation of the double-wavephotometry, i.e., a close binary system, is investigated. Howeverunlikely, we discuss how the observed period change might be reconciledwithin a model of a strongly interacting binary. Third, aninterpretation of a non-radial multi-mode pulsator is investigated. Theobserved period change and the multi-frequency behaviour do support thisinterpretation. We propose that the pulsational mode l=1 and |m|=1 maymimic a ``binary'' light- and radial-velocity curve. However, thephasing of the radial velocity and the light curve may be inconsistent.The possibility l=2 and |m|=0 is also discussed. Finally, we suggest howthe enigma of the variability of WR 46 may be solved.
| The VIIth catalogue of galactic Wolf-Rayet stars
The VIIth catalogue of galactic PopulationI Wolf-Rayet stars providesimproved coordinates, spectral types and /bv photometry of known WRstars and adds 71 new WR stars to the previous WR catalogue. This censusof galactic WR stars reaches 227 stars, comprising 127 WN stars, 87 WCstars, 10 WN/WC stars and 3 WO stars. This includes 15 WNL and 11 WCLstars within 30 pc of the Galactic Center. We compile and discuss WRspectral classification, variability, periodicity, binarity, terminalwind velocities, correlation with open clusters and OB associations, andcorrelation with Hi bubbles, Hii regions and ring nebulae. Intrinsiccolours and absolute visual magnitudes per subtype are re-assessed for are-determination of optical photometric distances and galacticdistribution of WR stars. In the solar neighbourhood we find projectedon the galactic plane a surface density of 3.3 WR stars perkpc2, with a WC/WN number ratio of 1.5, and a WR binaryfrequency (including probable binaries) of 39%. The galactocentricdistance (RWR) distribution per subtype shows RWRincreasing with decreasing WR subtype, both for the WN and WC subtypes.This RWR distribution allows for the possibility ofWNE-->WCE and WNL-->WCL subtype evolution.
| Tailored Analyses of the WN 8 Stars WR 40 and WR 16
We present the results of tailored spectral analyses of two WN 8Wolf-Rayet stars: WR 40 (HD 96548) and WR 16 (HD 86161). These analyseswere carried out utilizing line-blanketed non-LTE model atmospheres withprovisions for a clumped wind. For the first time in WN analyses,stellar parameters are derived by attempting to match the entireobserved spectrum from 900 to 35000 Å, including the complex ironpseudocontinuum between 1200-2100 Å. The inclusion of iron andother metals (O, Ne, Mg, Al, Si, S, Ar, and Ca) in the model atmosphereresults in a decrease in derived stellar radii by ~20% from previous,nitrogen-line analyses, while mass-loss rates are decreased by a factorof ~3 owing to clumping. The abundance of iron and other metals areconstrained with uncertainties of about 50%, demonstrating thatWolf-Rayet stars can be used to determine metallicities and metallicitygradients in other galaxies. We find the presence of metalssignificantly increases the radiative line force the wind experiences,allowing the outer wind to be driven to its theoretical velocitystructure and coming within a factor of 5 of the needed line force inthe inner region (an improvement over earlier radiative transfermodels). Coupled with the substantial reduction in the derivedperformance numbers (factor of ~3), this indicates that radiationpressure alone may be sufficient to drive the winds of WN 8 stars. Ourmodel parameters achieve good fits simultaneously to the H, He, and NIII-IV features of the spectra, a feat that has eluded previous efforts.Comprehensive identification of lines and line complexes are provided,and the effects of the inclusion of metals on the strengths ofdiagnostic lines are discussed.
| Exospheric models for the X-ray emission from single Wolf-Rayet stars
We review existing ROSAT detections of single Galactic Wolf-Rayet (WR)stars and develop wind models to interpret the X-ray emission. The ROSATdata, consisting of bandpass detections from the ROSAT All-Sky Survey(RASS) and some pointed observations, exhibit no correlations of the WRX-ray luminosity (LX) with any star or wind parameters ofinterest (e.g. bolometric luminosity, mass-loss rate or wind kineticenergy), although the dispersion in the measurements is quite large. Thelack of correlation between X-ray luminosity and wind parameters amongthe WR stars is unlike that of their progenitors, the O stars, whichshow trends with such parameters. In this paper we seek to (i) test byhow much the X-ray properties of the WR stars differ from the O starsand (ii) place limits on the temperature TX and fillingfactor fX of the X-ray-emitting gas in the WR winds. Adoptingempirically derived relationships for TX and fXfrom O-star winds, the predicted X-ray emission from WR stars is muchsmaller than observed with ROSAT. Abandoning the TX relationfrom O stars, we maximize the cooling from a single-temperature hot gasto derive lower limits for the filling factors in WR winds. Althoughthese filling factors are consistently found to be an order of magnitudegreater than those for O stars, we find that the data are consistent(albeit the data are noisy) with a trend of fx ∝(Mν&infy;)-1 in WR stars, as is also the casefor O stars.
| The photometric and spectroscopic characterization of the V Sagittae star V617 Sagittarii
Photometric and spectroscopic characterization of the V Sge star V617Sgr (WR 109) is presented. The orbital period, 0.207 day, is theshortest of its class. The optical light curve presents a double wavewith minima and maxima of uneven brightness. Strong emission lines ofhighly ionized species such as HeII, NV and OVI dominate the opticalspectrum. High and low photometric states have been observed and theprimary eclipse becomes shallower at eruptions. H? emissionbecomes stronger and broader at high state when compared to low state.The striking similarities to V Sge are discussed. The photometric andspectroscopic observations suggest that a high and asymmetric rim existsassociated with the accretion disk. This star is interpreted as a X-rayquiet galactic counterpart of the supersoft X-ray binaries seen in theMagellanic Clouds. Based on observations made at LaboratórioNacional de Astrofísica/CNPq, Brazil, and Cerro TololoInteramerican Observatory--CTIO, Chile.
| Wolf-Rayet stars before and after Hipparcos.
Not Available
| Coupled Line-Profile and Continuum Variations in EZ Canis Majoris: Implications for the Driving Mechanism of Global Wind Structures in Wolf-Rayet Winds
EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequencethat exhibits strong variations on a period of 3.77 days with coherencylasting typically about 10 cycles. We have used an extensive set ofoptical spectroscopic observations to investigate a possible linkbetween its line-profile and photometric continuum variability. Despitethe strong epoch dependency of the variations, a persistent correlationis found between changes in the wind line profiles (N V lambda lambda4604, 4620 in particular) and in continuum flux emanating near thestellar core. We suggest that these observations give further support tothe idea that the physical conditions prevailing in the vicinity of thestar's photosphere have a significant impact on the wind structure andthat a spatial dependence of these conditions at the base of the outflowinduces the formation of azimuthal wind structures in EZ CMa. Theepoch-dependent nature of the variability could be related to long-termbehavior of corotating magnetic structures, although pulsationalinstabilities constitute a viable alternative.
| The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTEradiation transfer calculations are performed which account for heliumand nitrogen. Grids of theoretical models are presented for the wholerelevant parameter range. The WN classification criteria are employed inorder to identify the subtype domains, and inconsistencies arediscussed. The (almost complete) sample of known Galactic WN stars isanalyzed by comparing the observed spectra with the synthetic spectra ofthe grid models. This is the first time that nitrogen line analyses areperformed for the whole WN sample, while previous comprehensive studieswere restricted to helium models. The obtained parameters roughlyconfirm the results from the previous helium analyses, as far as latesubtypes (WNL) and early subtypes with strong lines (WNE-s) areconcerned. For early subtypes with weak lines (WNE-w), however, theparameters are substantially revised. The hottest WN star, with astellar (effective) temperature of 140kK, is WR2, which could not beanalyzed previously from its helium lines due to the lack of He I. Theother members of the WNE-w subgroup have stellar temperatures between 40and 90kK, thus populating the same temperature range as the strong-linedWNE-w, but with less dense winds. The luminosities are revised accordingto the new parameters. Moreover, reddening corrections are newlydetermined form comparing IUE data with the UV model fluxes. The averageluminosity is now log L/Lsun = 5.5 for WNE stars (both,strong and weak lined), and log L/Lsun = 5.9 for WNL (notsignificantly revised). The empirical minimum WN luminosity is10(5.0}L_{sun) , reducing former incompatibilities with predictions fromevolutionary calculations. The ratio between mechanical and radiativemomentum flow is slightly affected by the revisions, but remains muchhigher than unity: 9, 9 and 29 for the WNL, WNE-w and WNE-s subclass,respectively. Partly based on observations collected at the EuropeanSouthern Observatory (ESO), La Silla, Chile, and on archival data fromthe International Ultraviolet Explorer (IUE)
| 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.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. II. Photometry
Abundant {HIPPARCOS photometry over 3 years of 141 O and Wolf-Rayetstars, including 8 massive X-ray binaries, provides a magnificentvariety of light curves at the sigma ~ 1-5% level. Among the mostinteresting results, we mention: optical outbursts in HD 102567 (MXRB),coinciding with periastron passages; drastic changes in the light curveshape of HD 153919 (MXRB); previously unknown long-term variability ofHD 39680 (O6V:[n]pe var) and WR 46 (WN3p); unusual flaring of HDE 308399(O9V); ellipsoidal variations of HD 64315, HD 115071 and HD 160641;rotationally modulated variations in HD 66811=zeta Pup (O4Inf) and HD210839=lambda Cep (O6I(n)fp); dust formation episode in WR 121 (WC9). Ina statistical sense, the incidence of variability is slightly higheramong the WR stars, which might be explained by the higher percentage ofknown binary systems. Among the presumably single WR stars, thecandidate runaways appear to be more variable then the rest. Based ondata from the ESA Hipparcos astrometry satellite
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.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/Abstract.html
| Photometric variability of the SMC W-R binary HD5980
We present the results of a photometric monitoring campaign of the W-Rbinary HD5980 conducted in November--December 1995, 16 months after theLBV-like outburst of one of the components of the system. On the basisof almost 800 y-band measurements, an improved orbital ephemeris isderived. We also report the discovery of a coherent 6h periodicoscillation visible in the Stromgren b and y bands with amplitudes ~0fm025 . This short period may be related to pulsations of the primaryor secondary component. Based on observations obtained at the EuropeanSouthern Observatory at La Silla, Chile (observing proposalsESO~56-D0392 and 56-D0249).
| Radio and infrared structure of the colliding-wind Wolf-Rayet system WR147
New, high-resolution infrared and radio images of the X-ray-luminousWolf-Rayet system WR147 (AS 431) are presented. The 5-GHz radio imageresolves both components of this double source. The emission from onecomponent, that to the south and associated with the wind of the WN8star, has an extent of ~170x253 mas^2, indicating that the stellar windis not spherically symmetric. The second, non-thermal component ~0.6arcsec north of the WN8 star is extended east-west to ~267mas. Theinfrared image reveals the presence of a companion to the WN8 star,close to the non-thermal radio source but slightly (~60 mas) moredistant from the WN8 star. The companion is DeltaK~3mag fainter than theWN8 star and has a luminosity of a B0.5V star, just sufficientlyluminous to possess a stellar wind capable of colliding with that of theWN8 star. The presence of the non-thermal emission between the two starsand much closer to that with the weaker wind is direct evidence for acolliding-wind origin for the emission. A significant portion of theX-ray emission can also be accounted for by the release of energy in thewind collision. Comparison of the non-thermal flux with those of thethree systems incorporating WC-type stars (WR125, WR140 and WR146) showsa correlation with velocity of the WR wind.
| The 73rd Name-List of Variable Stars
Not Available
| A Survey of Nebulae around Galactic Wolf-Rayet Stars in the Southern Sky. III. Survey Completion and Conclusions
We present the conclusion of a narrow-band optical CCD survey ofWolf-Rayet stars in the southern portion of the Milky Way. In this partof the survey we complete our survey of the southern Galaxy and reportthe detection of 10 new optical nebulae associated with Wolf-Rayetstars. This brings the final survey total to 40 Wolf-Rayet stars withassociated nebulae in 114 southern Galactic fields for a 35% detectionrate. Our results suggest that the Galactic environment has littleapparent effect on the detection rate of nebulae associated withWolf-Rayet stars. Indeed, a more important role in the production ofnebulae is likely to be played by the evolution of the central star. Thesurvey results also suggest a slightly higher incidence of nebuladetection around WN stars over WC stars, although nebulae associatedwith WC stars are noted as being generally larger and some may have beenmissed through being larger than the CCD array used. Indeed, theincreased rate of nebula detection compared to that of a northernGalactic survey can be accounted for solely through the fact that alarger region of sky around the Wolf-Rayet stars was imaged in oursouthern survey as compared to the northern survey. Larger nebulaeexisting around WC as opposed to WN stars are also consistent with thecurrent theory of the evolution of Wolf-Rayet stars from WN to WC.
| Large IRAS Shells Around Galactic Wolf-Rayet Stars and the O Star Phase of Wolf-Rayet Evolution
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....112.2828M
| A three-dimensional classification for WN stars
A three-dimensional classification for WN stars is presented using (1)the HeII 5411/HeI 5875 ratio as a primary indicator of ionization, (2)FWHM 4686 and EW 5411 as indicators of line width and strength, and (3)an oscillating Pickering decrement as an indicator of the presence ofhydrogen. All WN stars in the Galaxy and two-thirds of the LMC stars areclassified on the new system. Almost all spectra inspected fall smoothlyinto categories within which the spectra are very similar. Allionization subclasses show a tight correlation between line strength andwidth, with stars containing hydrogen at the weak, narrow end, and WN/Cstars near the strong, broad end. H^+/He^++ correlates with strength andwidth with a cut-off for the presence of hydrogen, which is slightlydependent on ionization subclass, at about FWHM 4686=30A and EW5411=25A. The correlations found indicate that high (initial) mass starsevolve as narrow-line stars from late to early ionization subclass.Lower (initial) mass stars evolve with increasing line strength andwidth, probably to earlier ionization subclass. The HeII 4686/NV,III4604-40 ratio shows a clear correlation with Galactocentric radius,presumably an effect of the Z gradient. CIV 5808/HeII 5411 shows no suchcorrelation. LMC WN stars can be classified without difficulty by thecriteria established for Galactic WN stars. While individual spectra ofa given subtype are similar in the two galaxies, the frequencydistributions over ionization subclass, over EW and FWHM in subclassesWN4 and WN5, and hydrogen content in subclasses WN6-8 are different. Theeffects are presumably due to metallicity, but the causal connection isunclear.
| Existence of a short period (3.5-4 hours) in the photometric variability of WR66.
We report here on an independent detection of a short period (~4hours)in the photometric variations of WR66, thus confirming in broad termsthe discovery by Antokhin et al.. In addition, we present the firstspectroscopic variability analysis for this star. A few peculiarities ofthe spectrum of WR66 are also discussed. Finally, we perform a briefexamination of different possible origins of the phenomenon.
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| Csillagkép: | Körző |
| Rektaszcenzió: | 15h14m57.70s |
| Deklináció: | -59°50'30.2" |
| Vizuális fényesség: | 11.45 |
| RA sajátmozgás: | -4.7 |
| Dec sajátmozgás: | -3 |
| B-T magnitude: | 12.194 |
| V-T magnitude: | 11.512 |
Katalógusok és elnevezések:
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