198 9ApJ. . . 347.1034R The AstrophysicalJournal,347:1034-1054,1989December15 © 1989.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. tering fromtheircopiousnumberoffreeelectrons.However, are potentialsourcesoflinearpolarizationviaThomsonscat- masses. (SeeBastien1989foradiscussionofretogradeorbits binaries, variousparametersarededuced,suchastheinclina- several singleWRstarsand+Obinarysystems.For the Paper I)containsgoodexamplesofpolarimetricbehavior net polarizationdifferingfromzerocanonlybeobservedinthe which werenotcorrectlyinterpretedatthetimeofPaper I.) tion oftheorbitalplane,whichleadstoestimatesstellar relative distributionofthelightsource(s)andscatterers. total lightfromthestarasaconsequenceofasymmetriesin The identificationoftime-dependentpolarimetricvariations in single WRstars(Drissenetal.1987;hereafterPaperII) pro- vides ausefulnewwaytoinvestigateintrinsicasymmetries in of binaries,tocalculatethemass-lossrate(M)WRcom- propose anewmethod,basedonthepolarizationmodulation the WRwindstructure.InPaperHI,St.-Louisetal.(1988) bright WRstarsinCygnus.Polarimetric dataoftheWR+O ponents. binary V444Cyg(HD193576), whichshowsapolarization 1 The firstpaperofthisseries(St.-Louisetal.1987;hereafter Because oftheirhot,intensewinds,Wolf-Rayet(WR)stars VisitingAstronomer,Universityof Arizona Observatories. This paperpresentspolarimetric dataforsevenoftheeight POLARIZATION VARIABILITYAMONGWOLF-RAYETSTARS.V.LINEAROF Cygnus Wolf-Rayet(WR)stars.ThesixWRstarsHD191765,192103,192163,192641, HD 190918behavesasexpectedforalong-periodWR+Osystemwithanellipticalorbit.Theeighthstar, HD 193077,and193793,showonlyrandom,low-amplitudemodulationontimescalesofhourstodays. V444 Cyg(HD193576),istheonlyshort-periodWR+ObinaryinCygnussampleandtreateddetail WR starsofvariousspectralsubtypes.Weconfirmaprevioussuspicionthatthedegreerandom,intrinsic especially forWNstars(comparedtoWCstars). caused bythepresenceofpropagatingblobs,whichform,survive,and/orgrowmoreeasilyinslowerwinds, scatter inpolarizationiscorrelatedwithspectralsubclassandterminalwindvelocity.Thisproposedtobe minal andthermalwindvelocities,themass-lossrate,stellarcoreradius.Itisnotclearifobserva- instability. Thismodelleadstoacorrelationbetweenthepolarizationscatterandcombinationofter- growth ratepredictedbyOwocki,Castor,andRybickifortheamplitudeofaradiativelydrivenline-shape 1 tions reproducethiscorrelation,becauseofuncertaintiesinthestellarparameters._ Subject headings:polarization—stars:binarieswindsWolf-Rayet wind velocity.Thismodelfitsthedatabetter,especiallyforWNstars,butisstillfarfromcompelling. tial ofthewindpropagatingtime.ThistimeisproportionaltoWRcoreradiusdividedbyterminal perturbation itself(ofunknownorigin),yieldsacorrelationbetweenthepolarizationscatterandexponen- u Carmelle Robert,AnthonyF.J.Moffat,PierreBastien,LaurentDrissen,andNicoleSt.-Louis © American Astronomical Society • Provided by the NASA Astrophysics Data System We reportprecisionbroad-bandbluelightmonitoringinlinearpolarizationofseventheeightbright The polarizationdatafortheeightbrightCygnusWRstarsarecombinedwithsimilar18other We developtwomodelstoexplaintheoriginofblobs.Thefirstmodelisbasedonexponential Another simpler,butmoreadhocmodel,whichrelatesthegrowthrateofdispersiontosize THE BRIGHTCYGNUSSTARSANDANANTICORRELATIONOFVARIABILITY I. introduction Département dePhysique,UniversitéMontréal;andObservatoireAstronomiqueduMontMégantic Received 1988June1;accepted198919 WITH WINDSPEED ABSTRACT 1034 eclipse ofthescatterers,istreatedmoreextensivelyina Cygnus WRstars,theoverallsampleofstarsmonitoredso separate paper(Robertetal.1989;hereafterPaperVI). far inhigh-precisionpolarimetryisnowcompleteforthewhole are nowrepresented. sky toF=9.2mag.Furthermore,mostoftheWRsubtypes cedures fortheeightbrightCygnusWRstars,includingV444 in §111.Theoverallsignificanceoftheintrinsicpolarimetric Cyg, aregivenin§II.Adiscussionofindividualstarsfollows were firstcollectedin1984MayandNovemberatthreediffer- § IV.AsummaryisgiveninV. variations inthenewlargesampleofobjectsissubject of ent telescopes:the1.52mofMountLemmon(Arizona), the carried outforthewholesample ofstarswiththe1.55mtele- Cygnus WRstarsarelistedinTable1.Theseparameterswere scope ofMountBigelowand the 1.02and1.52mtelescopesof Mégantic (Québec).In1985 Octobermeasurementswere gathered mainlyfromthecatalogofvanderHuchtetal.(1981). in 1986October.Mostofthe observations weremadewiththe during anothervisittothe1.02 mtelescopeofMountLemmon Mount Lemmon.Theobservations werethencompleted 1.55 mofMountBigelow(Arizona),andthe1.60Mont With thenewpolarimetricobservationsforeightbright The observationsandadiscussionofthereductionpro- Polarimetric dataforoneobjectpresentedhere,HD192163, The spectraltypesandthemagnitudesofeightbright II. OBSERVATIONSANDANALYSIS 198 9ApJ. . .347.1034R arized starswerealsoobservedinordertocalibratetheorigin polarization wasthenappropriatelysubtracted).Manypol- at MontMégantic,wherePi„s^0.15%;thisinstrumental instrumental polarization(P<0.010%)foreachrun(except it wassomewhatworsein1984. obtained in~15minutesforeachobject1985and1986, diaphragm of~10"diameter.Aprecision<7<0.015%was (centered at4700ÂwithaFWHMbandpassof1800Â)using surements weremadethroughablueCorningfilter4-96 type describedbyAngelandLandstreet(1970).Allthemea- University ofArizona.Onlyafewdata(thosefromMont Mégantic) werecollectedwithaPockelscellpolarimeterofthe t inst MINIPOL polarimeter(FreckerandSerkowski1965)ofthe P (see texttordetails).^ an O-typecompanion.TheabsorptionlinesofHD192641and193077havealsobeenproposed,somewhatlessconclusively,toariseinOstarcompanion 193793. 193576. 193011. 192641. 192163. 192103. 191765. 190918. The observationsofunpolarizedstarsrevealednegligible Note. ThecatalogofvanderHuchtetal.1981classifiedHD193793asaWC7+abssystem.Nowthereisgoodevidencefortheabsorptionlinestobedue HD © American Astronomical Society • Provided by the NASA Astrophysics Data System WR 140 139 138 137 136 135 134 133 WC7 +04V WN5 +06 WN5 +abs WC7 +abs WN6 WC8 WN6 WN4.5 +09.5la Spectral Type POLARIZATION VARIABILITYAMONGWRSTARS.V. General InformationfortheEightBrightCygnusWRStars (mag) 7.4 8.6 8.5 8.3 8.0 8.5 8.6 7.6 b 0.402 0.688 0.225 0.954 0.472% 1.367 1.175 1.450 0.033 0.032 0.030 0.027 0.023 0.023 0.044 0.024% star. Theparameterofct(P)isthescatterinPdefinedby and 0=iarctan(U/Qj]observedhereforeachCygnusWR 1036 vectors ofthesurroundingstarshaveaverychaoticpattern. polarization. FromFigure1,onecanseethatthepolarization large fluctuationsintheinterstellarandpossiblyintrinsic claimed tobetotallyofinterstellarorigin.Insomecasesthe case wheretheaveragedpolarizationcanbeunambiguously where Nisthenumberofdatapointscollectedforastarand are similar.Thediscrepanciesprobablymainlycausedby two anglesareclose;inothercasesthedegreesofpolarization tion withtheinterstellarvaluedoesnotrevealanyparticular of abinary.ComparisontheobservedaverageWRpolariza- WR starorthephase-dependentresultofbestfitincase are themeansofStokesparametersincaseasingle 1 alsocontainstheaveragepolarization[P=(Q+U) 1985 foradescriptionofthemethodusedtocalculatethese G istheobservationalerrorofP.ValuesQ,Uand periastron passageJD2,431,967.8). Solid curvesarethebestfittoeccentricmodel.Measurementsfrom 1985and1986areplottedwithasteriskscircles, respectively. Verticalbars,hereandin allthefigures,are2aerrorestimatespurelyduetophotonstatistics. Pj0Is lsIS Pitmm9 2u Fig. 2.—StokesparametersQand U forHD190918plottedagainstorbitalphase,calculatedusingthe FBH ephemeris(112.8dayperiodandthetimeof a(P) =£(jrfliQi-ÔJ+Vim)l>(i) © American Astronomical Society • Provided by the NASA Astrophysics Data System ROBERT ETAL. for thewell-knownbinaryHD190918.TheWR+Osystem with alongperiod,HD193793,istreatedinthesecondpart, V444 CygwillbediscussedindetailPaperVI. the singlestar,HD192103.Theshortperiodeclipsingsystem HD 192163and191765,arethenconsidered,followedby HD 192641and193077.ThesuspectedWR+csystems, along withthetwopossiblecandidatesforawideorbit, ible withitsbinarynature.Figure2showstheparametersQ found asmallamplitudeofvariationintheradialvelocitydata emission linesandnarrowabsorptionlines.Wilson(1949) The solidcurvesofFigure2areobtainedwiththeeccentric deduced byFraquelli,Bolton,andHorn(1987,hereafterFBH). calculated withthenewspectroscopicperiod,112.8+0.5days, and thetimeofperiastronpassage,ID2,431,967.8+1.6, and UfromTable2,plottedagainstorbitalphase,whichwas and thenqualifiedthisobjectasabinarysystem. see SimmonsandBoyle1984): orbit modelofBrownetal.(1982)whichgives(aftercorrection; =1 +ecosA2 First, wepresentanddiscussthepolarimetricdataobtained 0' (rr^p[(-¿i The polarizationdatacollectedforHD190918arecompat- The spectrumofHD190918iscomposedbroad,diluted cos2 III. RESULTSANDDISCUSSIONOFINDIVIDUALSTARS U' =77—{1+e—'U)isin22,(2) a) TheWR+OBinaryHD190918{WR133): (1 —e) WN4.5 +09.5la 2 x [(1+cosi)2À—sin/], Vol. 347 198 9ApJ. . .347.1034R No. 2,1989 longitude butgivenwithrespecttothelineofnodes).Theangle eccentric anomalyandKepler’sequation.Theparametert*is where Àistheorbitallongitudeofscatteringregion,mea- and corresponds toretrogrademotion.Notethatunlikethecaseof the parametersgivenbyFBH: by Q.ThequantitiesQandUcorrespondtotheaveragelevel between themajoraxisofellipseinQ—Uplaneand tude ofperihelion,isgivenbyÀ(deducedfromco,thesame the orbitalinclinationandeccentricity,respectively.Thelongi- related totheelectrondensityaroundWRstar;iandeare sured fromtheplanecontainingorbitalaxisandEarth. the complimentaryangleofi(givenby180°—=165°),which It iscalculatedintheusualwayfromorbitalphase,via tric modelwiththepolarimetricobservationswasfound M forthe09.5lacompanion.Betteragreementofeccen- of QandU.ThemodelcurvesFigure2werecalculatedwith g-axis (takenparalleltothecelestialnorthpole)issymbolized FBH calculatedaninclination^15°assumingamassof30 0 pWR 0 © American Astronomical Society • Provided by the NASA Astrophysics Data System U =+Q'sinQU'cosQ,, ô =6o+Ô'cosQ—17'sin, 0 À =œ—90°306°±8°, pWR from FBH. 706.683. 730.638. 728.724. 728.613. 724.729. 722.710. 721.729. 720.719. 718.755. 716.827. 712.631. 711.822. 704.787. 371.765. 369.722. 367.802. 366.786. 366.575. 364.754. 363.751. 362.704. 734.642. 733.666. 732.641. 731.704. 729.697. 726.737. 723.741. 735.690. 3 e =0.48±0.04, (2,446,000 +) Theorbitalphaseiscalculatedusing the112.8dayperiodandtimeofperiasronpassageJD2,431,967.8 Sources.—(1) 1985,MountLemmon andMountBigelow.(2)1986,Lemmon. Julian Date i =165°. POLARIZATION VARIABILITYAMONGWRSTARS.V. 0.453 0.472 0.481 0.465 0.462 0.425 0.464 0.466 0.480 0.438 0.450 0.497 0.466 0.496 0.424 0.444% 0.458 0.479 0.451 0.473 0.500 0.518 0.509 0.469 0.495 0.485 0.464 0.481 0.460 Linear PolarizationDataforHD190918 0.020 0.009 0.011 0.006 0.009 0.008 0.006 0.007 0.004 0.008 0.009 0.010 0.012 0.012 0.012 0.016 0.009 0.007 0.016 0.008 0.008 0.008 0.008 0.009 0.006 0.011 0.012 0.014 0.005% 165.5 162.3 158.1 158.7 161.8 161.3 161.5 161.4 163.9 161.0 161.8 161.6 163?3 157.5 157.7 159.1 160.4 160.0 158.2 157.7 158.8 160.4 161.0 159.4 160.6 162.2 161.8 164.3 163.7 e (3) TABLE 2 0°3 0.5 0.4 0.4 0.2 0.5 0.5 0.6 0.7 0.7 0.8 0.6 0.6 0.4 0.7 0.4 0.6 0.5 0.5 0.5 0.5 0.5 0.4 0.7 0.7 0.8 an 2 an 1.2 1.0 1.0 the polarizationorbit,radiovelocityorbitcannotdis- tinguish betweeniand180°—i.Thebestfitwasobtainedfor close to130°. eqs. [2]and[3]).Becauseofthelackdataattime related totheamplitudeofQand1/inadifferentmanner(see periastron passage(cp=0).Thispartoftheorbitiscrucialin cover onlyaboutone-thirdoftheorbitandavoidtime coupled toi,whiletheotherparametersÍ2,Go»dU compared totheotherknownWRstarswithsupergiantcom- and T*.Nevertheless,Qseemstobeconstrainedavalue periastron passage,wecannotyetestimateprecisevaluesofi determining iandt*becausetheseparametersaredirectly remained almostunaffected.Unfortunately,theobservations The errorsgivenfortheseparametersareverycrudeestimates panions, yVeland9Mus(PaperI).Forallthreebinaries,the polarization aroundtheeccentricorbitmodelofHD190918, observations. Forthesemodels,t*wasfoundtobestrongly a gridofdifferentvaluesQ,t^,Go»dto- based onvisualinspectionofcurvessuperposedthedatafor 0 It isalsoworthnotingtherelativelysmalldispersionin other modelswithdifferentvaluesofiwerealsofittedtothe 0.391 0.341 0.367 0.375 0.357 0.331 0.374 0.375 0.375 0.382 0.339 0.397 0.389 0.361 0.360 0.366 0.413 0.375 0.351 0.324 0.336 0.383 0.362 0.346 0.376 0.366 0.374 0.399 0.371% -0.324 -0.336 -0.301 -0.299 -0.321 -0.357 -0.357 -0.316 -0.343 -0.307 -0.305 -0.286 -0.327 -0.301 -0.268 -0.277 -0.294 -0.292 -0.255 -0.242 -0.249 -0.274 -0.226 -0.286 -0.229 -0.277 -0.278 -0.262 -0.244% U =-0210%±0.005%. Go =0.360%±0.005%, 0 T* =0.020±0.005, u Q =130°±20°, 3 Phase 0.664 0.651 0.633 0.921 0.912 0.894 0.876 0.868 0.858 0.824 0.815 0.806 0.797 0.771 0.754 0.717 0.709 0.647 0.695 0.677 0.660 0.649 0.624 0.614 0.903 0.886 0.859 0.842 0.788 Source 1037 198 9ApJ. . .34 7.1034R 2 light oftheOsupergiantdominates,butforyVeland9Mus conclude thattheOstarcompanioninHD190918isarela- nonradial pulsations(NRP)ofthesupergiant.Onemustthen the scatterinpolarizationisrelativelyhigh,possiblybecauseof tively stablesupergiant. motion. tionable becauseofthelackdetectablebinaryorbital qualify thesestarsasbinarysystems.Thislaterbecameques- HD 193077,and193793,originallyledastronomersto stars, inthespectraofthreeCygnusWRstarsHD192641, (Williams, vanderHucht,andThé1987),wasclaimedtobe pilation oftheIRemissionandradialvelocitydata. has finallybeenestablishedunequivocallyafteralongcom- a separationof0"05. stars failedtorevealanycompanionof|Am<2magdown Conti etal.(1984)forHD193793,wasvirtuallyeliminatedby a dropofMforfree-freeemissionmodel.AnIRburstthen 1038 Grasdalen 1979).Thisburst,aswelloneobservedin1985 occurred atthebeginningof1977(Hackwell,Gehrz,and sion between1970and1975.Thisbehaviorwasinterpretedas Moffat etal.(1986).Theirspeckleinterferometryforthesethree The presenceofabsorptionlines,similartothoseseeninO The possibilityofachanceline-of-sightOstar,proposedby The existenceofanorbitingOcompanioninHD193793 Hackwell etal.(1916)observedareductionoftheIRemis- © American Astronomical Society • Provided by the NASA Astrophysics Data System i) HD193793{WR140):WC7+04V b) WR+absObjects Fig. 3.—StokesparametersQandU plottedasafunctionofJulianDateforHD193793.SymbolsareinFig. 2. JULIAN DATE-2,446,000.0 ROBERT ETAL. (observed justbeforetheperiastronpassage)aretriggeredby (1987), confirmedthelongperiod(7.9±0.2yr,withtimeof mation. ionization WRstars(WC9andsomeWC8)tendtobesur- (see alsoWilliamsetal.1978).Itisknownthatlate-type,low- emission (BeckerandWhite1985)nonthermal fied atperiastron. with themassesfoundforstarsofsimilarspectraltypeinother 0.7. Theresultingmassesofeachcomponentarecompatible periastron passageID2,423,069+35)andaneccentricityof data, includingnewobservations,repeatedbyMoffatetal. periodicity of7.9yremerged.Theanalysisradialvelocity data andradialvelocitymeasurementsforHD193793,along does notgenerallyvary,implyingaconstantrateofdustfor- rounded bydustshells.However,theIRfluxfromthesestars related tothetriggeringofdustcondensationsaroundstar presented inFigure3andTable3.Asearchforperiodicity with thenormalstellarwind. among WRstars(Pollock1987).TheX-rayfluxesmeasuredin HD 193793istheintrinsicallybrightestX-raysourceknown Gottesman 1977;Florkowski1982;AbbottandConti1987). at atimecoincidingwiththeIRbursts(Florkowskiand the collisionoftwostellarwinds,whichisgreatlyintensi- systems. Williamsetal.(1987)proposedthattheIRbursts 1977 and1984(afteranIRburst)wereneverthelessassociated The presentpolarimetricobservationsofHD193793are The radiospectrumofHD193793hasshownbothfree-free Finally, whenWilliamsetal.(1987)combinedallexistingIR Vol. 347 198 9ApJ. . .347.1034R No. 2,1989 (using twodifferentprograms:onebasedonthenonpara- metric methodofLaflerandKinman1965,theotherby any significantperiods. Lamontagne 1983basedonfittingsinewaves)failstoreveal passage, showmarginallymorescatterthanin1986.(The these databecauseofinadequatephasecoverage.Nevertheless, tions of1985,whichareclosertothetimeperiastron one smallclueinfavorofthislongorbitisthattheobserva- The periodof7.9yrcannotbeverifiedyetonthebasis © American Astronomical Society • Provided by the NASA Astrophysics Data System 069 fromMoffatetal.1987. from thenobservations. filter centeredat4700ÂwithAA=1800 Â). Coyne 19742,440,416&1.47 34.4 20.012 Hall 1958-2,433,284No1.2% 35° 2-0.5 1985, MountLemmon2,446,366B1.354 32.9 100.074 1986, MountLemmon2,446,725B1.373 32.6 220.198 d c 321/ h TheBfilterusedbyCoyne1974is centered at—4300ÂwithA2—1000(differentfromourB Theorbitalphaseiscalculatedwith the7.9yrperiodandtimeofperiastronpassageJD2,423, P=(Q+t7).Theerrorfor indicatedinparenthesesisthestandarddeviationdeduced 0=jarctan(U/Q). and MountBigelow(0.052) 735.575. 733.751. 732.585. 731.789. 729.781. 728.684. 727.782. 725.596. 721.771. 721.615. 720.738. 718.784. 712.882. 708.603. 734.699. 730.775. 726.679. 724.739. 723.625. 722.734. 716.647. 710.593. 371.774. 369.787. 367.692. 366.767. 365.814. 364.560. 362.798. 366.743. 364.780. 363.741. 3 (2,446,000+) SourcesasinTable2. Julian Date POLARIZATION VARIABILITYAMONGWRSTARS.V. 3b 0 Reference MeanJDFilterP0 n Phase Average LinearPolarizationValuesforHD193793 1.377 1.398 1.329 1.361 1.402 1.385 1.384 1.389 1.358 1.380 1.380 1.363 1.371 1.377 1.371 1.361 1.392 1.377 1.337 1.376 1.364 1.366 1.424 1.346 1.369 1.383 1.395 1.313 1.349 1.387 1.313 1.264% Linear PolarizationDataforHD193793 0.011 0.009 0.010 0.015 0.012 0.005 0.009 0.008 0.008 0.008 0.011 0.013 0.014 0.013 0.007 0.005 0.009 0.010 0.010 0.008 0.006 0.010 0.013 0.012 0.006 0.004 0.010 0.009 0.010 0.017 0.007 0.008% TABLE 4 TABLE 3 32.7 33.0 31.6 32.3 32.8 33.2 33.4 32.1 32.5 32.2 32.5 32.3 33.7 32.1 33.0 33.4 34.1 3m 32.7 32.5 32.2 33.0 32.4 32.9 33.4 32.6 32.7 32.9 32.7 33.0 32.6 32.3 6 different domainsofwavelengthobserved. Table 4,aredifferentforeachgroupofdata.Littlecanbesaid different observers.Orbitalphases,giveninthelastcolumnof behavior, explainingwhythescatterisgreaterinUthanQ) orbital inclinationmightalsoplayanimportantroleinthis be afunctionofthewavelengthincidentphoton,but about thebinarymodulationinpolarizationbecauseof Table 4containsaveragevaluesoflinearpolarizationfrom The polarizationfromelectronscatteringisnotexpectedto 0.2 0.2 0.2 0.3 0.2 0.2 0.1 0.2 0.2 0.2 0.3 0.3 0.2 0.3 0.1 0.1 0.1 0.2 0.4 0?2 0.2 0.2 0.2 0.2 0.2 0.3 0.1 0.2 0.3 0.1 0.2 0.2 (0.017) 0.567 0.597 0.569 0.569 0.532 0.592 0.589 0.616 0.552 0.563 0.576 0.596 0.574 0.595 0.561 0.588 0.559 0.540 0.578 0.571 0.527 0.582 0.593 0.594 0.547 0.596 0.581 0.517 0.549 0.515 0.551 0.590% 1.257 1.277 1.218 1.225 1.258 1.255 1.231 1.242 1.261 1.249 1.243 1.260 1.250 1.237 1.254 1.229 1.247 1.230 1.271 1.251 1.219 1.315 1.228 1.233 1.263 1.268 1.207 1.288 1.247 1.232 1.192 1.118% u 3 Source 1039 198 9ApJ. . .347.1034R interstellar contributiontotheobservedpolarizationis,on electron scattering. cantly variablecomponentofpolarization,alsowavelength cised, however,sincedustformationanddissipationare No periodicityisfoundafterasearchthrougheachgroupof Niemela (1981)andbyMoifatetal.(1986)showednoclearsign interval of~12yrbetweentwosuccessiveIRbursts(Williams, electron density,ortheradiusofenvelope,asaconse- These variationswereclaimedtoariseinchangesofM,the Williams etal.1985)andthenbecamebrighterafter1978. has shownunusuallystrongvariations.Between1970and dependent, whichwouldaddtotheorbitalcomponentfrom thought tooccurinthesystem.Dustcouldproduceasignifi- the presentpolarimetricdata(1985or1986),throughall smallest levelofpolarimetricvariations(Fig.4andTable5). tions beendetectedsofar(Cherepashchuk1975a;Moifatand of duplicity.Neitherhaveanysignificantphotometricvaria- binary inanellipticalorbit,muchlikeHD193793. van derHucht,andThé1987)thisstarmightbealongperiod quence ofcondensationanddissipationdustshells.Withan other hand,wavelengthdependent.Cautionshouldbeexer- 1040 Shara 1986). 1975, theIRfluxslowlydecreased(Hackwelletal1976; The analysisofradialvelocitydatabyMassey,Conti,and As inthecaseofHD193793,IRemission192641 Among theCygnusWRstars,HD192641alsoshows © American Astronomical Society • Provided by the NASA Astrophysics Data System ii) HD192641{WR137):WC7+abs Fig. 4.—StokesparametersQandU plottedasafunctionofJulianDateforHD192641.SymbolsareinFig. 2. ROBERT ETAL. single star. presence ofdustcouldalsoconfusepossiblevariationsbetween zero in1968.Theconstancyofthenewdataisconsistentwith HD 192641canalsobesimplyinterpretedasifarisingina the differentepochsofdata.Thepolarizationdata unknown wavelengthdependenceofthepolarizationor time oflargeseparationforawideeccentricbinary.The this period,sincethenewobservationsfallatlonglasting correlated totheIRdecreaseof1970-1975.Wesupposethata emission model.TheIRandX-rayfluxbehavior(Pollock degree ofpolarization.ThelastcolumnTable6showsthe burst occurredaround1968,leadingtoanincreaseofthe parameters foreachgroupofnewdataandotherprevious orbital phasesfora12yrperiodusinganemphemerisofphase observation 1yrlater(JD2,440,854)inthesamefiltercouldbe obtained byCoyneatJD2,440,416(1969)comparedtothe observations (Hiltner1951;Coyne1974).Thehigheraverage these datatogether.Table6containstheaverageStokes Gehrz, andSmith(1974)waseasilyexplainedbyafree-free emission-producing envelope.Thiscouldimplythatthereis series. Intrinsicabsorptionlinesareusuallyfoundonlyin responsible fortheabsorptionlinesdominatedbyBalmer still hydrogenintheWRphotosphere,whichmaybe 1987) appearsnormalsofar. The IRemissionofHD193077observedbyHackwell, Massey (1980)claimedtohavediscoveredhydrogeninthe ni) HD193077(WR138):WN5+abs Vol. 347 198 9ApJ. . .347.1034R No. 2,1989 just starting(thewindsarelessdensethaninmoreevolved period of1749days(or1533asaclosesecondpossibility) previous observationsofBracher(1966),Massey(1980),and (1980) concludedthatHD193077isasingle,rapidlyrotating he claimednottohavefoundanysignificantvariationsofthe massive WNLstarsforwhichtheWRtypemass-lossprocessis velocity analysisbyLamontagne(1983),whichincludedthe WR starwithalow-densityH-richwind.Amorerecentradial tion linesarebroaderthanthoseseeninmostOstars,Massey radial velocity(coveringarangeof15yr)andthattheabsorp- WNE orWCstars).Nevertheless,combinedwiththefactthat Lamontagne etal(1982),revealedapossibleorbitwith © American Astronomical Society • Provided by the NASA Astrophysics Data System 0 d on theIRdata). and Thé1987,theephemerisfor thetimeofperiastronpassagearound1968:JD2,439,856(based Hiltner 1951-2,433,284No1.2% 168° ?-0.5 Coyne 19742,440,854B1.19 168.3 20.228 Coyne 19742,440,416£1.36 169.1 20.128 1986, MountLemmon2,446,724B1.175 167.5 220.567 1985, MountLemmon2,446,366B1.174 167.0 60.485 d b a c SameasinTable4. SameasinTable4. SameasinTable4. Theorbitalphaseiscalculatedwith theapproximate12yrperiod,fromWilliams,vanderHucht, and MountBigelow(0.027) 3 710.661 1.152 709.611 1.154 707.685 1.167 362.762 1.171% 732.668 1.186 730.699 1.141 729.744 1.171 727.729 1.160 724.655 1.186 722.666 1.181 721.675 1.175 720.672 1.184 718.702 1.137 717.736...... 1.150 712.828 1.160 371.755 1.153 367.764 1.180 366.667 1.207 364.737 1.190 363.725 1.163 735.716 1.179 734.670 1.187 733.708 1.217 731.735 1.178 728.651 1.188 725.703 1.208 724.787 1.130 723.693 1.154 a (2,446,000 +)P0p0VoQUSource SourcesasinTable2. Julian Date POLARIZATION VARIABILITYAMONGWRSTARS.V. ah c Reference MeanJDFilterP9 n Phase Average LinearPolarizationValuesforHD192641 Linear PolarizationDataforHD192641 0.011 167.60.31 0.010 167.50.21 0.010 168.00.21 0.012 167.60.31 0.010 167.40.31 0.012 167.00.31 0.016 167.70.41 0.011 165.80.31 0.007 167.70.21 0.009 166.90.21 0.010 166.40.21 0.005 166.70.11 0.010 167.90.21 0.007 168.20.21 0.012 167.60.31 0.009 167.60.21 0.010 167.90.21 0.009 167.90.21 0.012 167.40.31 0.010 167.90.21 0.009 168.00.21 0.014 167.30.31 0.014 168.50.31 0.011 167.20.31 0.016 168.00.41 0.009 167.30.21 0.027 168.00.71 0.009% 168?40?21 TABLE 6 TABLE 5 be verifiedyet.TheaveragedStokesparametersmeasured cient timespan,thesuggestedlongperiodof1538dayscannot cant periodicitywasfoundinthesedata.Becauseofaninsuffi- confirmed andrefinedtheorbitofLamontagne(1983)witha of 1538days,thereare~8.6orbitalcyclesbetweeneachepoch around 1950fornonfilteredlight(Hiltner1951)arevery HD 193077arepresentedinFigure5andTable7.Nosignifi- period of1538days. WN6 +Owasalsogiven.MorerecentlyAnnuk(1989)has and reasonablevaluesforthemasses.Arevisedspectraltypeof similar totherecentobservations(Table8).Withaperiodicity The smalltemporalvariationsofthepolarizationfor (0.021) .083 -0.4822 .042 -0.4642 .063 -0.4912 .084 -0.4872 .051 -0.4902 .102 -0.4952 .022 -0.4812 .053 -0.4732 .079 -0.4802 .067 -0.4932 .070 -0.5082 .059 -0.4492 .046 -0.5012 .035 -0.5052 .049 -0.4802 .014 -0.5481 .073 -0.4911 .058 -0.5441 .040 -0.5211 .083 -0.4872 .099 -0.5222 .087 -0.4752 .069 -0.4942 .029 -0.4842 .066 -0.4752 .083 -0.5331 .070 -0.4952 .076% -0.461%1 1041 198 9ApJ. . .347.1034R found forasinglestar,butthisdoesnoteliminatethepossi- 1042 bility ofalongorbit. of data.Thefewpolarimetricobservationsresemblethose claimed tobeaneutronstar(accordingtheinterpretationof centered onHD192163,showsaprominentfilamentarystruc- known aroundanyWRstar.Thethin,ellipsoidalshell,nearly by ring-shapednebulosity.NGC6888,associatedwith HD variability ofHD192163byAslanovandCherepashchuk Aslanov, andCherepashchuk1982theradialvelocity the photometricvariabilityofHD191765byAntokhin, and HD192163.Ineithercase,thelow-masscompanionis be WR+cbinaries.ThesearethetwoWN6starsHD191765 nebulosity. Oneofthemsimply invokestheinteractionof hypotheses havebeenproposedtoexplaintheformationof the ture (Wendkeretal1975).Thenebulosityassociatedwith HD with thepresenceofacompact companion;thenebulosityis principle. Otherinvestigators haveassociatedthenebulosity and Hogg1965)shouldbe visiblearoundanyWRstarin Bruhweiler, andGull1982;TreffersChu1982).Several supposed tohavebeenformed bymasstransferfromtheWR stellar windwiththeambient interstellarmedium(Johnson 192163, isthenearest,brightestandmostregularnebulosity 1981). 191765 formsamorediscretefilamentarybubble(Heckathorn, Two ofthebrightCygnusWRstarshavebeensuspectedto These twoobjectsshareanotherpoint:theyaresurrounded © American Astronomical Society • Provided by the NASA Astrophysics Data System c) WR+cCandidates Fig. 5.—StokesparametersQandUplottedasafunctionofJulianDateforHD193077.Symbolsarein2. ROBERT ETÁL. photometry ofMoffatandShara (1986).Vreux,Andrillat,and that thisperiodwaslessfavourable thanthealiasperiodsof vious radialvelocitydatasupplemented bynewmeasurements, Gosset (1985)haveargued,from asecondanalysisofthepre- velocity dataofLamontagne (1983)andinthebroad-band polarization data.Thisperiodicity wasalsoabsentintheradial found originallyinthelineprofilevariationsofKoenigsberger, Antokhin andCherepashchuk(1985),isnotpresentherein the Aslanov andCherepashchuk(1981),inthephotometry of Firmani, andBisiacchi(1980),intheradialvelocitydata of spectroscopic andphotometricdata.The4.554dayperiod, any oftheperiodicitiesclaimedinpastonbasis of was ejectedonashorttimescale(Lozinskaya1980). excluded here. may beduetothedifferenceineffectivewavelength.Thepossi- in Figure6andTable9.showsshorttimescalevaria- progenitor intothecompactcompanionatsucharapidrate an unknowncompanioninawideellipticalorbitcannot be bility ofasuddenorslowchangeMeventheexistence of deviates considerablyfromlaterobservations.Thediscrepancy that thecompanionbecamebloatedandmuchofmatter of thepolarizationdatapublishedbyHall(1958)(seeTable 10) tions inQandUofrelativelylowamplitude.Themeanvalue 1984 to1986inthesamebroad-bandbluefilterarepresented The polarimetricvariabilityofHD192163doesnotreveal The normalizedStokesparametersQandUobservedfrom i) HD192163{WR136):WN6 Vol. 347 198 9ApJ. . .347.1034R 2 2 to adegreecomparabletheprecisiondesiredhere). This period wastestedforreliabilityaccordingtoaprogrambased on themethodofNemecand(1985),whichconsists in the dataof1984collectedatMontMéganticbecause,that With the1984and1986datacombinedtogether,most periods, 2.778and1.558days(correspondingtothefrequency repeating theperiodicitysearchmanytimesinsetsof data a fewpolarizedstandards,whicharenowknowntobevariable time, theefficiencyofpolarimeterwascalibratedusing only significant periodis7.080days,withx—0.5(wehaveomitted ior. Themostsignificantperiodfoundinthe1986dataaloneis 7.157 days,withanaveragexfor6andUof0.5.Thealias through thepolarimetricdata. periods failstoreproduceanytypeofcontinuouswave could beduetoNRP.However,eitherofthesetwoshort 0.45 or0.31day.Therefore,theysuggestedthatthevariations No. 2,1989 Hiltner 1951-2,433,284No0.7%103° ? 1986, MountLemmon2,446,123 B0.688100.521 1985, MountLemmon.....2,446,367 B0.682101.28 a b SameasinTable4. SameasinTable4. and MountBigelow (0.039) A systematicsearchforperiodicityrevealsinterestingbehav- of the7.157dayperiod),alsoshowupatsamelevel. ab Reference MeanJDFilterP0n Average LinearPolarizationValuesforHD193077 © American Astronomical Society • Provided by the NASA Astrophysics Data System 735.733. 734.686. 733.733. 732.653. 731.717. 729.763. 728.668. 727.707. 725.684. 724.680. 723.672. 722.683. 721.786. 721.655. 720.639. 718.727. 717.649. 712.862. 710.643. 709.591. 704.866. 371.730. 369.799. 367.757. 366.676. 365.800. 364.707. 363.732. 362.776. a (2,446,000+) TABLE 8 SourcesasinTable2. Julian Date POLARIZATION VARIABILITYAMONGWRSTARS.V. 0.711 0.651 0.672 0.676 0.684 0.699 0.718 0.679 0.731 0.689 0.663 0.720 0.646 0.687 0.711 0.693 0.685 0.687 0.686 0.723 0.768 0.700 0.649 0.679 0.691 0.739 0.627 0.635 0.684% (0.025) Linear PolarizationDataforHD193077 0.010 0.009 0.010 0.009 0.010 0.014 0.011 0.011 0.011 0.010 0.009 0.007 0.014 0.011 0.012 0.014 0.016 0.011 0.010 0.014 0.018 0.006 0.012 0.008 0.012 0.010 0.010 0.013 0.010% TABLE 7 101.3 102.7 101.1 100.5 101.3 100.0 100.2 100.6 100.3 100.5 101.6 100.0 104.5 103.0 100.2 102.1 100.0 100.5 100?5 100.4 99.8 99.2 98.4 99.8 99.3 99.5 99.3 99.1 99.7 0 2 2 2 value ofxforQandU. metric observationscombined togetherrevealedabestperiod are manyrandompermutations ofthedatathatyieldasimilar of 1.2707days,withanaverage xforQandUof0.66.There neutron star. effect wasexplainedbyaWR+cbinarywithprocessing indicates irregularvariationsoveratimescaleofmonths. This (1986). ThephotometryofAntokhinandVolkov(1987)clearly days) fromthebroad-bandphotometryofMoffatandShara (1984) and(b)the1.7844dayperiodfromradialvelocity data ofLamontagne(1983)and(withasimilarvalue 1.81 double-wave curvesinQandU.Theperiodstestedwere(a) the vations: 1984(withouttheMontMéganticdata),1985,and disappeared whenthesearchwascarriedthroughallobser- icity ratherquestionable.Finally,the7.080dayperiodalmost and Cherepashchuk(1982)Antokhin deduced inotherstudies,failedtoreproducesimultaneous dispersion. 7.483 dayperiodfromthephotometryofAntokhin,Aslanov, WR -bOsystems,HD191765showsthelargestpolarimetric bright CygnusWRstars,excludingbinarymodulationinthe (from Table11)observedforHD191765.Amongtheeight value ofx—0.5.Thismakesthepossibilityarealperiod- permutations aroundthe7.080dayperiodyieldedasimilar formed byrandomlymixingtheobservationsintime.Afew 1986. 0.4 0.4 0.4 0.5 0.4 0.4 0.4 0.6 0.4 0.4 0.4 0.3 0.6 0.5 0.5 0.6 0.7 0.5 0.4 0.6 0.7 0.2 0.5 0.3 0.5 0.4 0.5 0.6 0?4 An independentsearchforperiodicity amongallthepolari- Flots ofQandUversusphase,calculatedwiththeperiod Figure 7showsaplotversustimeoftheparametersQandU -0.640 -0.660 -0.638 -0.625 -0.665 -0.607 -0.650 -0.666 -0.657 -0.639 -0.643 -0.652 -0.675 -0.706 -0.658 -0.568 -0.610 -0.648 -0.674 -0.589 -0.593 -0.639% -0.670 -0.618 -0.628 -0.647 -0.631 -0.653 -0.680 ii) HD191765{WR134):WN6 -0.226 -0.314 -0.260 -0.222 -0.277 -0.221 -0.224 -0.248 -0.221 -0.248 -0.242 -0.214 -0.259 -0.303 -0.239 -0.315 -0.298 -0.241 -0.303 -0.214 -0.228 -0.245% -0.239 -0.205 -0.239 -0.195 -0.263 -0.250 -0.229 U 3 Source 1043 198 9ApJ. . .347.1034R o 5 © American Astronomical Society • Provided by the NASA Astrophysics Data System 1044 i 10 o o Q S £ § \¿ -supergiant star.Thesample alsoincludesthetwobinaries two binariescontainingasupergiant companion,yVeland0 underlying starorofinstabilitiesarisingintheline-drivenwind gested thattheycouldbetheconsequenceofNRPin the Mus, sincetheirvariationsmay beassociatedwithNRPofthe stars (seeTable13).Thenewsampleincludesallstudied found withtheterminalvelocity(t;^):fast-windstarstend to late-subtypes, i.e.,WC9andWN8stars.Acorrelationwas also (excluding anyorbitalmodulation),andspectralsubtype,for origin oftheblobsisstillunknown;inPaperII,itwas sug- as thepresenceofblobsinwind,whicharemorestable in that thelargestamplitudesofpolarizationareassociated with persion amplitudeoftheintrinsicpolarimetricvariations ejection inthewind. slow winds(fasttendtohomogenizetheoutflow). The show lessscatterinpolarization.Theseresultswereinterpreted studied indetailPapersIandII).Thiscorrelationshowed sic variationsprobablyrelatedtoasymmetricandstochastic 11 WRstars(polarimetricobservationsofthesewere 0.4 0.2 0.4 0.3 0.6 0.7 0.3 0.3 0.3 0.3 0.4 0.3 0.3 0.3 0.3 0.4 0.3 0.4 0.4 0.4 0.3 0.4 0.3 0.3 0.3 0.2 0?2 0.3 0.3 0.2 0.3 We repeatthisanalysishere,usingalargersampleof26WR In PaperII,acorrelationwasfoundbetweencr(P),thedis- IV. INTRINSICPOLARIMETRICVARIABILITYOFWRSTARS 0.998 0.936 0.891 0.982 0.961 0.936 0.897 0.966 0.901 0.922 0.909 0.914 0.930 0.948 0.880 0.922 0.912 0.969 0.994 0.971 0.969 0.888 0.974 0.902 0.940 0.926 0.899 0.927% 1.052 1.003 1.041 -0.035 0.053 0.219 0.187 0.148 0.088 0.040 0.208 0.155 0.095 0.166 0.081 0.085 0.149 0.154 0.128 0.095 0.109 0.134 0.112 0.161 0.174 0.183 0.250 0.098 0.140 0.073 0.200 0.102 0.026 0.255% u Source® 1047 198 9ApJ. . .347.1034R 2 firmed. VariationsinthesuspectedWR+csystemsarealso considerably shorterthanthelongperiodsproposedorcon- is expectedareassumedtobeintrinsictheWRstar,notdue (WC7 +04V)andtheWRabssystemswhereacompanion y Veland6Mus.ThevariationsobservedforHD193793 variations duetothesupergiantcompanion,asincasesof retained inthesample,sinceitshowsnoevidenceforstrong HD 190918,alsoabinarywithsupergiantcompanion,is consider theWRstarEZCMa(HD50896)inthisanalysis to orbitalmodulation,sincethetotalobservingintervalwas ior (thispeculiarobjectisthesubjectofaseparatepaper by because ofthedifficultyininterpretingitspolarimetricbehav- assumed tobeassociatedwiththeWRstarsonly.Wedo not (WN2, WN3,WC4,andWO)aremissing. concerned; onlyhotWRstarsofextremespectralsubtypes Drissen etal1989).Despitetheseomissions,thesample is 1048 almost completeasfarcoveringstarsofdifferentsubtypes is mental errordhasbeensubtracted: P, asdefinedbyequation(1),fromwhichtheaverageinstru- Values ofo>canvaryfrom0.010% to0.042%. that theWCstarsareclearlylocated belowtheWNstarsof sion tendstooccuramongthe latesubtypesoflowionization. WC andtheWNstars.Asnoted inPaperII,thelargestdisper- Because thepresentsampleincludes morestars,onenowsees P The parametera(P)giveninTable13isthenetscatter in Figure 10showso{P)versus spectralsubtypeforboththe net net © American Astronomical Society • Provided by the NASA Astrophysics Data System 2 °(P)L =«(P)-¿1■(4) Fig. 9.—StokesparametersQandUplottedasafunctionofJulianDateforHD192103.Symbolsarein2. ROBERT ETAL. WC databytwosubclassesinthehotterdirection.Partof WC-WN differencebecomeslesspronouncedaftershiftingthe artifact ofthepeculiardefinitionsubtypes;indeed same numericalsubtype(e.g.,WC7vs.WN7).Thismaybean harbor acompactcompanion(boldsymbol)areequallyinter- value of<7(P)assmallthatsometheWCstars. difference isreal,however,sincetherenoWNstarwitha nitude (MfromvanderHuchtetal1988)revealsa very Table 13;someofthesevaluesareatpresentunderrevision by the WR+Osystemsdonotappeartodiffersignificantlyfrom one candidatesuspectedtohaveacompactcompanion).Also, spersed amongtheotherWNstars(theWCincludeonly Furthermore, Figure10showsthattheWNstarssuspectedto ably becauseitincludesmore stars.Again,thereisatrendfor Williams andEenens1989a,b andmighthavetobereducedby M (e.g.,LundströmandStenholm1984). the knowncorrelationbetweenWRspectralsubtype and similar correlation,asseeninFigure10.Thisisexpectedfrom posed ofalate-subtypeWN8,WC8,orWC9star. that thesampledoesnotincludeanyWR+Obinarycom- the singleWRstarsafterallowingfororbitalmodulation.Note WN starsthaninFigure10; theyarelocatednearthelower variation. TheWCstarsare not bettermergedherewiththe slower windstodisplaylarger amplitudesofpolarimetric Paper IIbetween2-3,havethestrongestphotometric(Lamontagne 5 net9 emission linescouldbedueto variousionscirculatinginmag- to harboracompactcompanion. Ontheotherhand, variations ofcertainWRstars thatwerepreviouslysuspected also suggestedbyVreux(1985)toexplaintheradialvelocity net spectroscopically determined pulsations(withperiodicity smaller thanhalfaday)inWR envelopes. Matthews andBeech(1987) have contestedVreux’sclaimfor nci There appears(notshown)tobealinearcorrelationbetween The existenceofsmallfluctuationsontimescaleshoursto Among theothertypesofinstability,greatattentionhas Underhill (1986)hasproposed thatmacroturbulenceinthe Yol. 347 198 9ApJ. . .347.1034R _1anc - 2 27v/vth where v^,R*,andMareexpressed inunitsofkms,R>* M© yr\respectively.Thenone findstherelation: give posed oftotallyionizedhelium(i.e.,p—nm/2),then For thecommonlyfoundvalueß=1,lastthreeequations vation, M=4nrvpconstant,and(c)theWRwindcom- where nistheelectrondensityand=4-^)'. («) aki,Vth) (P)net ^e”,(5) V th POLARIZATION VARIABILITYAMONGWRSTARS.V. 1 becomes homologous windsdiffering only inscale),equation(13)then If weassumeaconstantvalue of/forallWRstars(i.e., With thetransformationx=rR~, between twofixedradiuslimitswheresignificantlightscatter wind-velocity lawofCastorandLamers(1979),integrated latter parametercanbeestimatedfromtheparameterized occurs: where aistheinitialamplitudeofperturbationat base of thewind,gisaconstant,andAioutflowtime. This growth occursandisobservablegives Simple integrationoverthestellarenvelopeinwhich bation itself: growth rateisproportionaltothemagnitudeofpertur- mention theassumptionsmade,wecannotmakeanydefinite conclusion aboutthevalidityofthismodeltoaccountfor observed innature,viz.,thattheinstantaneousperturbation observations. Itisbasedonthesimplehypothesiscommonly observed polarizationdispersion. tional uncertaintiesintheparametersR*,v,andnotto parameter kofeq.[5])evenchangesfrompositivetonegative (1986) orfromBarlow,Smith,andWillis(1981).Thedifferent according tothesourceofMused.Becauselargeaddi- show anystrongcorrelation.Theslope(correspondingtothe equation (10)calculatedwiththedifferentsourcesofMdonot plots (notpresentedhere)ofIn[cr(P)]versustherightside 0 values ofMusedareeitherfromPaperIII,Abbottetal The valuessocalculatedforR*aregiveninTable13. equivalent widthsoflinesintheWNandWCstarsequences. corresponding tothedifferencebetweenmassesand polation fortheotherspectralsubtypes.Thesamerelationis also usedfortheWCstars,butwithashiftinspectralsubclass from Leung,Moffat,andSeggewiss1983).Therefore,wesimply M oc—2.5logLvs.subclass;seeLundströmandStenholm of WNstars(asoneobservesforotherparameterssuchas assume alinearrelationbetweenlogR*andspectralsubclass ing WNstarsV444Cyg(R*=2.9R©fromCherepashchuk, The stellarradiiarenotwellknown,exceptforthetwoeclips- where mistheelectronmassandkBoltzmanncon- Eaton, andKhaliullin1984)HD214419(R*=11.2R© tral typearetakenfromtheresultsofSmithandWillis(1981). stant. TheelectrontemperaturesforWRstarsofdifferentspec- th 1984). ThisassumptionallowsustoestimateR*byinter- expressed bymeansoftheelectrontemperatureT: net observations, weassumethatthethermalvelocityissimply v R*,andM.Tocompareequation(10)withthepolarimetric v eB e th9 Out ofcuriositywealsotryanothermodeltoexplainthe 1 1*.v{r)Vnl(1-RJrf' Rt dr - r—-—r** ^)net 1(1-l/xf■ Voo qAt dcr(P) nct (T(P) =. C,Bieging,J.H.,Churchwell,E.,andTorres,A.V.1986,Ap.J., outward alongwiththegeneralwind.Precisionspectropolari- emission-line profileofHen¿5411insometheCygnusWN stars studiedhere;thebumpsappeartobeaccelerated have recentlyrevealedsmallbumpsofvariousstrengthsinthe resolution emission-lineprofilestudies.Moffatetal(1988) asymmetries inthewind.Onewillalsohavetoresorthigh- give onlyaglobalmeasureofthevectorialsumall used todescribeatypicalsingleblobbyitself,sincesuchdata No. 2,1989 5,45. (FBH). 137. Reidel), p.63. tions, Physics,Evolution,ed.C.W.H.deLooreandA.J.Willis(Dordrecht: (Paper II). Weeren, N.,andvanGenderen,A.M.1989,Ap.J.,343,426. 774. 1986a, Ap.J.,304,188.’ 198,787. N. 1988,A.J.,95,900. al. (Vatican:VaticanObservatory),p.595. (Dordrecht: Reidel),p.139. in Galaxies,ed.C.W.H.deLoore,A.J.Willis,andP.Laskaridos Letters, 8,156. 303,239. Continuum linearpolarimetricdataalonecannotbeeasily © American Astronomical Society POLARIZATION VARIABILITYAMONGWRSTARS.V. REFERENCES Provided bythe NASA Astrophysics Data System .19896,M.N.R.A.S.,submitted. Williams, P.M.,andEenens,R.J. 1989a,inIAUSymposium113,Physicsof Williams, P.M.,Beattie,D.H.,Lee, T. J.,Steward,J.M.,andAntonopoulov, Wendker, H.J.,Smith,L.F.,Israel,F. P.,Habing,H.J.,andDickel,R.1975, Vreux, J.-M.,Andrillat,V.,andGosset, E.1985,Astr.Ap.,149,337. Vreux, J.-M.1985,Pub.A.S.P.,97,274. van derHucht,K.A.,Hidayat,B.,Admirante,A.G.,Supelli,R.,andDoom van derHucht,K.A.,Conti,P.S.,Lundström,L,andStenholm,B.1981,Space van derHucht,K.A.,Cassinelli,J.P.,andWilliams,P.M.1986,Astr.Ap., 168, Treffers, R.R.,andChu,Y.-H.1982,Ap.J.,254,569. Underhill, A.B.1986,Pub.A.S.P.,98,897. Torres, A.V.,Conti,P.S.,andMassey,1986,Ap.J.,300,379. St.-Louis, N.,Moffat,A.F.J.,Drissen,L.,Bastien,P.,andRobert,C.1988, Ap. St.-Louis, N.,Drissen,L.,Moffat,A.F.J.,Bastien,P.,andTapia,S.1987, Ap. Smith, L.J.,andWillis,A.J.1983,inWolf-RayetStars:ProgenitorsofSuper- Simon, N.R.,andStothers,R.1970,Astr.Ap.,6,183. Simmons, J.F.L.,andBoyle,C.B.1984,Astr.Ap.,134,368. Schumann, J.D.,andSeggewiss,W.1975,inIAUSymposium67,Variable Schmidt, G.D.1988,inPolarizedRadiationofCircumstellarOrigin,ed.V. Rybicki, G.B.1987,inInstabilitiesLuminousEarlyTypeStars,ed.H.J. Ross, L.W.1961,Pub.A.S.P.,73,354. Robert, C.,Moffat,A.F.J.,Bastien,P.,St.-Louis,N.,andDrissen,L.1989,in Pollock, A.M.T.1987,Ap.J.,320,283. Owocki, S.P.,Castor,J.L,andRybicki,G.B.1988,Ap.J.,335,914(OCR). Noels, A.,andScuflaire,R.1986,Astr.Ap.,161,125. Noels, A.,andGabriel,M.1981,Astr.Ap.,101,215. Nemec, A.F.L.,andJ.M.1985,A.J.,90,2317. Moffat, A.F.J.,andShara,M.1986,92,952. Moffat, A.F.J.,Lamontagne,R.,Williams,P.M.,Horn,andSeggewiss,W. Moffat, A.F.J.,Lamontagne,R.,Shara,M.M.,andMcAlister,H.1986, Moffat, A.F.J.,Drissen,L.,Lamontagne,R.,andRobert,C.1988,A.J.,334, Matthews, J.M.,andBeech,M.1987,Ap.J.,313,L25. Massey, P.,Conti,P.S.,andNiemela,V.S.1981,Ap.J.,246,145. Massey, P.1980,Ap.J.,236,526. Maeder, A.1985,Astr.Ap.,147,300. Lundström. L,andStenholm,B.1984,Astr.Ap.Suppl,58,163. Lucy, L.B.,andWhite,R.1980,Ap.J.,241,300. Lozinskaya, T.A.1980,SovietAstr.Letters,6,193. Leung, K.-C,Moffat,A.F.J.,andSeggewiss,W.1983,Ap.265,961. Lamontagne, R.,Moffat,A.F.J.,Koenigsberger,G.,andSeggewiss,W.1982, Lamontagne, R.,Moffat,A.F.J.1987,J.,94,1008. Québec. the FormationdeChercheursetl’AideàlaRechercheof ciated. WeacknowledgefinancialsupportfromtheConseilde Williams onthefirstdraftofpaperaregratefullyappre- Recherche enSciencesNaturellesetGénieofCanadaand time. UsefulcommentsbyK.vanderHucht,S.Owocki,andP. from theSpaceTelescopeScienceInstitute.Wealsothank was providedbyNSFgrantINT82-13103and0006-85 polarimeter. SupportforthemaintenanceofMINIPOL Steward Observatoryforthegenerousallotmentofobserving J. Moffat(Dordrecht:Kluwer),inpress. Luminous BlueVariables,ed.K.Davidson, H.J.G.L.M.Lamers,andA.F. E. 1978,M.N.R.A.S.,185,467. Astr. Ap.,42,113. C. 1988,Ap.J.,199,217. Sei. Rev.,28,227. J, 330,286(PaperIII). J., 322,870(PaperI). p. 113. 111. Evolutions, ed.C.W.H.deLooreandA.J.Willis(Dordrecht:Reidel), novae?, ed.M.C.LortetandA.Pitault(Obs.deMeudon),p.III.79. Stars andStellarEvolution,ed.V.E.SherwoodL.Plant(Dordrecht: Reidel), p.299. Coyne etal.(Vatican:VaticanObservatory),p.641. préparation (PaperVI). L. M.LamersandC.W.H.deLoore(Dordrecht:Reidel),p.175. ÆJ., 91,1392. 1987, Ap.J.,312,807. 1038. Ap. J.,253,320. We aregratefultoS.TapiafortheuseofMINIPOL . 1981,in/AUSymposium99,Wolf-RayetStars:Observations,Physics, 1053 198 9ApJ. . .347.1034R Nicole St.-Louis:DepartmentofPhysicsandAstronomy,UniversityCollegeLondon,GowerSt.,LondonWC1E6BT,England, UK Montréal, C.P.6128,Suce.A,PQ,CanadaH3C3J7 Pierre Bastien,LaurentDrissen,AnthonyF.J.Moffat,andCarmelleRobert:DépartementdePhysique,Université Williams, P.M,Longmore,A.J.,vanderHucht,K.A.,Talevera, Williams, P.M.,vanderHucht,K.A.,andThé,S.1987,Quart.J.R.A.S.,28, 1054 Wansteker, W.M.,Abbott,D.C,andTelesco,C.M.1985,M.N.R.A.S.,215, 23. 248. © American Astronomical Society • Provided by the NASA Astrophysics Data System ROBERT ETAL. Williams, P.M,vanderHucht,K.A.,Woerd,H.,Wamsteker,W.M., Willis, A.J.1982,M.N.R.A.S.,198,897. Wilson, O.C.1949,Ap.J.,109,76. Geballe, T.R.,Garmany,C.D.,andPollock,A.M.1987,inInstabilities Luminous EarlyTypeStars,ed.H.J.G.L.M.LamersandC.W.de Loore(Dordrecht: Reidel),p.221.