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The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars
The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksecXMM-Newton, observation, implying an upper limit to the X-ray luminosityof LX < 2.5x 1030 erg s-1 andto the X-ray to bolometric luminosity ratio ofLX/Lbol < 4*E-9. This confirmsindications from earlier less sensitive measurements that there has beenno convincing X-ray detection of any single WC star. This lack ofdetections is reinforced by XMM-Newton, and CHANDRA observations of WCstars. Thus the conclusion has to be drawn that the stars withradiatively-driven stellar winds of this particular class areinsignificant X-ray sources. We attribute this to photoelectronicabsorption by the stellar wind. The high opacity of the metal-rich anddense winds from WC stars puts the radius of optical depth unity athundreds or thousands of stellar radii for much of the X-ray band. Webelieve that the essential absence of hot plasma so far out in the windexacerbated by the large distances and correspondingly high ISM columndensities makes the WC stars too faint to be detectable with currenttechnology. The result also applies to many WC stars in binary systems,of which only about 20% are identified X-ray sources, presumably due tocolliding winds.
| Kinematical Structure of Wolf-Rayet Winds. I.Terminal Wind Velocity
New terminal wind velocities for 164 Wolf-Rayet stars (from the Galaxyand LMC) based on PCyg profiles of lambda1550 CIV resonance line werederived from the archive high and low resolution IUE spectra availableform the INES database. The high resolution data on 59 WR stars (39 fromthe Galaxy and 20 from LMC) were used to calibrate the empiricalrelation lambda_min^Abs- lambda_peak^Emis vs terminal wind velocity,which was then used for determinations of the terminal wind velocitiesfrom the low resolution IUE data. We almost doubled the previous mostextended sample of such measurements. Our new measurements, based onhigh resolution data, are precise within 5-7%. Measurements, based onthe low resolution spectra have the formal errors of approx 40-60%. Acomparison of the present results with other determinations suggestshigher precision of approx 20%. We found that the terminal windvelocities for the Galactic WC and WN stars correlate with the WRspectral subtype. We also found that the LMC WN stars have winds slowerthan their Galactic counterparts, up to two times in the case of the WNEstars. No influence of binarity on terminal wind velocities was found.Our extended set of measurements allowed us to test application of theradiation driven wind theory to the WR stars. We found that, contrary toOB stars, terminal wind velocities of the WR stars correlate only weaklywith stellar temperature. We also note that the terminal to escapevelocity ratio for the WR stars is relatively low: 2.55 pm 1.14 for theGalactic WN stars and 1.78 pm 0.70 for the Galactic WCs. This ratiodecreases with temperature of WR stars, contrary to what is observed inthe case of OB stars. The presented results show complex influence ofchemical composition on the WR winds driving mechanism efficiency. Ourkinematical data on WR winds suggest evolutionary sequence: WNL -->WNE --> WCE --> WCL.
| 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.
| 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.
| Radio Continuum Measurements of Southern Early-Type Stars. III. Nonthermal Emission from Wolf-Rayet Stars
The Australia Telescope Compact Array (ATCA) has been used to search forradio continuum emission at 2.4 and 1.4 GHz from a sample of 36 southernWolf-Rayet stars. Seven Wolf-Rayet stars were detected at 2.4 GHz, ofwhich two were also detected at 1.4 GHz. We have identified sixWolf-Rayet stars, WR 14, 39, 48, 90, 105, and 112, that have nonthermalemission. The ATCA data confirm that at least 40% of Wolf-Rayet starswith measured spectral indices have nonthermal emission at centimeterwavelengths. Properties of each of the six sources are discussed. Themeasured spectral indices are between 0 and -1.0, and the radioluminosities are of order 10^29 ergs s^-1. So far 10 confirmed sourcesof nonthermal emission are known, including the six ATCA detections andfour previously known cases, WR 125, 140, 146, and 147. In all cases,the nonthermal radio emission almost certainly originates from aninteraction between the Wolf-Rayet stellar wind and the wind from amassive companion star. The radio observations agree well withtheoretical predictions for colliding winds. Synchrotron emission occursfrom relativistic electrons accelerated in strong shocks. The nonthermalspectral indices are likely to be close to -0.5. For WR 39, the detectedradio emission is offset by ~3" from the optical position of WR 39 andby ~2" from the optical position of WR 38B. We suggest that the radioemission may originate from a wind-wind interaction between WR 39 and WR38B, although this is not confirmed. For WR 11, the radio spectral indexincreases from +0.3 between 3 and 6 cm to +1.2 between 13 and 20 cm.This is interpreted as evidence for a highly attenuated nonthermalcomponent that originates well within the ionized wind of the W-R starfrom an interaction with the wind of the O9 companion star.
| 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
| Quantitative classification of WC and WO stars
We present a quantitative classification scheme for carbon and oxygensequence Wolf-Rayet stars. Our scheme uses new high-quality optical AATand INT observations of 20 stars for which we provide narrow-bandphotometry and estimates of interstellar reddenings. In increasing orderof excitation, our spectral classes range from WC11 to WC4 forWolf-Rayet stars with a dominant carbon line visual spectrum, andsubsequently from WO4 to WO1 for those with predominantly oxygen lines.We refine existing WC and WO schemes to incorporate stars with higherand lower excitation spectral features. Both massive stars and centralstars of planetary nebulae (CSPNe) can be classified with the unifiedsystem. We have found no criterion that cleanly separates spectra of thetwo types of star, including elemental abundances (C/O or C/He).However, CSPNe show a wider range of line strength and width thanmassive stars in the same ionization subclass. Systematically lowerFWHM(Civ lambda5808) values are observed from WO-type CSPNe than frommassive WO stars. For WC4-11 stars, our primary diagnostic is theequivalent width or line flux ratio Civlambdalambda5801-12/Ciiilambda5696. We extend the use of this as theprincipal criterion throughout the WC sequence, with fewreclassifications necessary relative to Smith, Shara & Moffat. ForWO stars, Ciii is absent and our new criteria, using primarily oxygenlines, take over smoothly. We define subclasses WO4-1, using Ovilambdalambda3811-34/Ov lambda5590 as our primary diagnostic. Thecontinuation in spectral sequence from WC to WO is used to indicate thatthe sequence is a result primarily of excitation effects, rather thansignificant abundance differences. Our scheme allows us to confirm thatmassive stars and CSPNe are differently distributed over the subclasses.Around 3/5 of massive WC stars lie within the range WC5-8, while<=1/5 of CSPNe are found within these spectral types. Stars withinboth the highest (WO1) and lowest (WC10-11) excitation spectral classesare unique to CSPNe. A WC classification for the hot RCrB star V348 Sgris excluded (previously [WC12]) since both Ciii lambda5696 and Civlambda5808 are absent in its optical spectrum. Additional criteria allowus to distinguish between WC-type, `weak emission line' CSPNe, and Ostars, allowing us to reclassify the central star of IRAS 21282+5050(previously [WC11]) as an O star.
| 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. 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
| Radio Continuum Measurements of Southern Early-Type Stars. II. A Distance-limited Sample of Wolf-Rayet Stars
A distance-limited sample of southern Wolf-Rayet stars within 3 kpc ofthe Sun has been observed with the Australia Telescope Compact Array at8.64 and 4.80 GHz. Radio continuum flux densities at one or bothfrequencies were obtained for 10 sources and upper limits for 20; foursources are found to be thermal emitters on the basis of the observedspectral index. Five sources are classified as nonthermal. One sourcecould not be classified. We derive mass-loss rates for the thermalsources. After combining them with all existing radio mass-loss rates ofWolf-Rayet stars in the northern and southern hemisphere, we perform acomparison with mass-loss rates derived from optical emission lines. Thetwo methods lead to consistent results, which suggests either that theassumption of a spherically symmetric, stationary, homogeneous stellarwind is correct or that deviations from this assumption affect bothmethods in the same way. Wolf-Rayet mass-loss rates are surprisinglyuniform across spectral type. We find an average mass-loss rate of 4 x10-5 Mȯ yr-1 for all types observed, except for WC9 stars, whichhave rates that are lower by at least a factor of 2. An alternativeexplanation could be partial recombination of helium from He+ to He0 inthe radio region, which would lead to a reduced number of freeelectrons, and therefore reduced radio flux for WC9 stars. Mass-lossrates of 8 x 10-5 Mȯ yr-1 for late WN stars favored in recentstellar evolution models disagree with the observations of thesesubtypes. The results of this survey suggest that ~40% of all Wolf-Rayetstars with measured spectral index are nonthermal emitters at centimeterwavelengths. This percentage is nearly twice as high as that ofnonthermal emitters among OB stars and is higher than that previouslyestimated for WR stars. The nature of the nonthermal emission is stillnot fully understood. Possible causes of nonthermal emission arediscussed. In particular, we speculate that nonthermal emission mayarise from an interaction between a thermal WR wind and surroundingmaterial owing to a shell ejected during a previous evolutionary stageor owing the wind of a companion star.
| 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
| H-beta Photometry of Southern Luminous Stars
H-beta photometry for 116 stars listed in Stephenson and Sanduleak's(1971) catalog of _Luminous Stars in the Southern Milky Way_ isreported. The vast majority of these objects are O and B-type stars; afew are A, F, or Wolf-Rayet stars. A systematic difference of on theorder of 30 mmag between the present results and those of otherinvestigators is noted. (SECTION: Stars)
| An IRAS-based Search for New Dusty Late-Type WC Wolf-Rayet Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..413C&db_key=AST
| Spectral analyses of 25 Galactic Wolf-Rayet stars of the carbon sequence.
We present a grid of helium-carbon models for Wolf-Rayet (WR) stars ofthe carbon sequence (WC) with β_ C_=0.2 (carbon mass fraction),thus extending our previously released grid with β_C_=0.6 to adifferent chemical composition. The WR model atmospheres are based onthe so-called standard assumptions. The calculations account for non-LTEradiation transfer in spherically expanding atmospheres. Helium andcarbon are represented by detailed model atoms, especially concerningthe ions Ciii and Civ. Using the model grids 25 Galactic WC stars ofintermediate subtype (WC5 to WC8) are analyzed. Subsequently we performfine analyses by calculating several individual models for each of theprogram stars. Temperatures, radii, mass-loss rates and terminalvelocities are determined together with the carbon to helium ratio. Theanalyzed WC stars are found to form two groups, which can bedistinguished by the strength of their emission lines. Stars with weaklines (WC-w) have effective temperatures close to 50kK and their windsare relatively thin, forming the continuous spectrum in regions withsmall expansion velocities. WC stars with strong lines (WC-s) havehigher effective temperatures (60 to 100kK, referring to the coreradius) and thick winds. Thus there is a strong analogy to thedistribution of the early-type WN stars (WNE-w and WNE-s, respectively).For the WC stars we determine luminosities between 10^4.7^ and10^5.5^Lsun_ and mass-loss rates from 10^-4.8^ to10^-3.9^Mȯ/yr. The carbon mass fraction varies from 0.2 to 0.6. Nocorrelation is found between the carbon abundance and any of the stellarparameters (e.g. temperature, luminosity) or the spectral subtype. Theevolution of WR stars is discussed by comparing the results of ouranalyses with evolutionary tracks.
| A Large Bubble External to the Wolf-Rayet Ring Nebula NGC 6888
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....109.2257M
| 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.
| Terminal Velocities of Wolf-Rayet Star Winds from Low Resolution IUE Spectra
Attracted by the simplicity of the recently published by Prinja (1994)method of determination of terminal wind velocities in hot stars fromlow resolution IUE spectra we investigate its application to WR stars.With a large sample of low resolution IUE spectra of WR stars we foundeven simpler, that is linear instead of square, empirical relationbetween Delta lambda as defined by Prinja (1994) and terminal windvelocity -- vinfty. Using this new empirical relation wepresent vinfty for a sample of 85 galactic and LMC stars, 19of them determined for the first time. We almost tripled the number ofterminal velocity determinations for LMC WR stars. The comparison withother determinations shows that this simple method is accurate to within10-20%. We confirm the correlation between terminal velocity and WCsubtype. We also show that terminal velocities of WN stars are lowerthan that of WCE. A comparison between galactic and LMC stars shows thatthe LMC WN stars have slower winds in most of WN subtypes.
| The ROSAT PSPC survey of the Wolf-Rayet stars
Not Available
| The interstellar medium around Wolf-Rayet stars: clues to evolution (Invited)
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| Low resolution IUE spectra of Wolf-Rayet stars.
We present uniformly reduced and measured equivalent widths, FWHM andobserved line fluxes for 94 "single" WR stars (34 galactic WN, 22galactic WC, 31 LMC WN and 7 LMC WC) based on the archive IUE spectra ofWR stars gathered from different observational runs and from differentepochs. The spectra are used for spectral classification in theultraviolet region and for searching correlations among the strength andwidths of emission lines of different ions. Some correlations withoptical and near IR lines observed by other authors are given as well.The set of spectra we use is almost complete to 12 magnitude andrepresentative according to spectral subtype of WR stars.
| The origin of extended interstellar shells around Wolf-Rayet stars having bright optical ring nebulae
Investigations of the interstellar environment around Wolf-Rayet (WR)stars have lead to the discovery of extended shells of gas and dust50-100 pc in diameter in the lines of sight toward three WR stars. Inthis paper, several origins for these extended shells are discussed.While positional coincidences cannot be excluded, the locations of theWR stars near the projected centers of the shells, the detection of onlyshortward-shifted, high-velocity UV absorption line components in theirIUE spectra, plus commonality of some WR star properties which are rarein the general WR star population suggest some casual connectionsbetween the WR stars and formation of interstellar shells. To accesswhether the high-velocity UV interstellar absorption lines are afrequent phenomenon related to WR stellar winds, we present a survey ofsuch features in all WR stars observed with IUE through 1991. Of 35stars studied, only four are found to have components with velocitydisplacements greater than 45 km/s which are not attributable topreviously identified OB association superbubbles. The means asurprising 82% of non-OB association WR stars show no evidence ofhigh-velocity gas in their lines of sight at IUE's spectral resolution,suggesting that high-velocity interstellar absorption lines are not acommon consequence of Wolf-Rayet star stellar winds alone. We review theproperties of three WR stars (HD 50896, HD 96548, and HD 192163) whichmay reside inside extended interstellar shells and find that they aresimilar in terms of spectral class (WN5-8), presence of an optical ringnebula, and reported photometric variability. Evaluation of possibleorigins of the extended shells suggests these three stars are in a postX-ray binary stage of high-mass binary star evolution. If this iscorrect, then the large interstellar shells detected might be evidenceof either supernova remnant shells generated by the explosion of thebinary's primary star, or non-conservative mass transfer during a RocheLobe overflow stage of the binary after the supernova explosion. Ineither of these cases the bright optical ring nebulae associated withthese three WR stars may signify recent Roche Lobe overflows consistentwith spectroscopic abundance analysis.
| A survey of nebulae around Galactic Wolf-Rayet stars in the southern sky, 1
Images are presented from the first half of a survey of all GalacticWolf-Rayet stars in the catalog of van der Hucht et al. (1981) residingin the southern skies. Previous surveys used only existing broad-bandphotographic plates. Encouraged by successes using CCD imaging withinterference filters of the LMC and northern Galaxy (Miller & Chu1993), we have expanded the survey to the southern hemisphere. In thefirst half of our southern survey, H alpha and (O III) narrow-band CCDimages of fields centered on known Wolf-Rayet stars have indicated theexistence of six new ring nebulae as well as revealing previouslyunobserved morphological features in the known ring nebulae. An exampleof this is an almost perfect ring of (O III) emission residing interiorto the previously observed H alpha filaments of the Wolf-Rayet ringnebulae RCW 104. Our surveys to date indicate that 21% of all Wolf-Rayetstars have ring nebulae, with WN-type Wolf-Rayet stars having a greaterlikelihood for an associated ring.
| Not Available
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| Spectrophotometry of Wolf-Rayet stars. I - Continuum energy distributions
All available low-resolution IUE spectra are assembled for Galactic,LMC, and SMC W-R stars and are merged with ground-based optical and NIRspectra in order to collate in a systematic fashion the shapes of theseenergy distributions over the wavelength range 0.1-1 micron. They can beconsistently fitted by a power law of the form F(lambda) isapproximately equal to lambda exp -alpha over the range 1500-9000 A toderive color excesses E(B-V) and spectral indices by removing the 2175-Ainterstellar absorption feature. The WN star color excesses derived arefound to be in good agreement with those of Schmutz and Vacca (1991) andKoesterke et al. (1991). Significant heterogeneity in spectral indexvalues was generally seen with any given subtype, but the groupsconsisting of the combined set of Galactic and LMC W-R stars, theseparate WN and WC sequences, and the Galactic and LMC W-R stars allshowed a striking and consistent Gaussian-like frequency distribution ofvalues.
| Search for H I bubbles around Wolf-Rayet stars between L = 302 deg and 312 deg
The results of a search for H I bubbles around the 14 WR stars known inthe section of the Galaxy between l = 302 deg and l = 312 deg arepresented. The results disclose four additional H I bubbles, all aroundWR stars at Galactic latitudes higher than absolute value of b = 2 deg.This increases to eight the number of known neutral gas bubblessurrounding WR stars. The new H I voids are associated with the WR stars52, 54, 57, and 61. The fact that no H I bubbles were found around WRstars close to the Galactic midplane is probably a selection effect.
| 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.
| Color excesses, intrinsic colors, and absolute magnitudes of Galactic and Large Magellanic Cloud Wolf-Rayet stars
A new method of determining the color excesses of WR stars in the Galaxyand the LMC has been developed and is used to determine the excesses for44 Galactic and 32 LMC WR stars. The excesses are combined withline-free, narrow-band spectrophotometry to derive intrinsic colors ofthe WR stars of nearly all spectral subtypes. No correlation of UVspectral index or intrinsic colors with spectral subtype is found forthe samples of single WN or WC stars. There is evidence that early WNstars in the LMC have flatter UV continua and redder intrinsic colorsthan early WN stars in the Galaxy. No separation is found between thevalues derived for Galactic WC stars and those obtained for LMC WCstars. The intrinsic colors are compared with those calculated frommodel atmospheres of WR stars and generally good agreement is found.Absolute magnitudes are derived for WR stars in the LMC and for thoseGalactic WR stars located in clusters and associations for which thereare reliable distance estimates.
| The distribution of massive stars in the Galaxy. I - The Wolf-Rayet stars
Using spectroscopic parallax, the heliocentric and Galactocentricdistances of nearly all of the 157 known Wolf-Rayet stars in the Galaxywere determined. Their distribution both within and perpendicular to theGalactic plane was investigated. The overall distribution within theplane reveals spiral features which are in accord with otherdeterminations of Galactic structure. In addition, it was found that theGalactocentric location of Wolf-Rayet stars is dependent on Wolf-Rayetsubtype, with late WC stars strongly confined to regions within thesolar circle. However, there is only a marginal variation in the WC/WNnumber ratio with distance from the Galactic center. The distribution ofWolf-Rayet stars in the direction perpendicular to the plane revealsthat these objects are closely confined to, but distributedasymmetrically about, the Galactic plane; the verical scale height ofthe distribution is about 45 pc. It is found that the sun is locatedabout 15 pc above the plane defined by these extreme Population Iobjects.
| Distances of Galactic WC stars from emission-line fluxes and a quantification of the WC classification
The extent to which later-type WC stars in the Galaxy show constant fluxin the carbon lines is assessed. It is found the the WC stars are anextremely 'well-behaved' sequence in terms of quantitative spectroscopicproperties. The two classification parameters are closely correlatedwith a scatter of the order of uncertainty. There appear to be naturalbreaks in the sequence between subclasses, except between WC5 and 6. Theclassification is quantified using the C IV 5808 A/C III 5696 A ratio asthe principal defining parameter for WC7-9 stars and the C III 5696 A/OV 5590 A ratio as the principal defining parameter for WC4-6 stars.Preliminary calibration of the line fluxes indicate that the flux of CIV 5808 A in Galactic WC stars is constant at F(0) 5808 = -logF(0)(5808) = 8.1 at 1 kpc for subclasses WC5-7. The intrinsic line fluxratio C(0) = log f(0)(5808/4650) is a smooth function of subclassnumber, decreasing from -0.22 dex for WC4 stars to -0.56 dex for WC9stars.
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| Csillagkép: | Kentaur |
| Rektaszcenzió: | 13h18m27.99s |
| Deklináció: | -58°08'13.6" |
| Vizuális fényesség: | 9.274 |
| RA sajátmozgás: | -3.4 |
| Dec sajátmozgás: | -2.8 |
| B-T magnitude: | 9.755 |
| V-T magnitude: | 9.314 |
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