THE ASTRONOMICAL JOURNAL, 115 :2047È2052, 1998 May1998. The American Astronomical Society. All rights reserved. Printed in the U.S.A.(

HUBBL E SPACE T EL ESCOPE DETECTION OF OPTICAL COMPANIONS OF WR 86, WR 146,AND WR 147 : WIND COLLISION MODEL CONFIRMED1

VIRPI S. NIEMELA2Facultad de Ciencias Astrono� micas y Geof•� sicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina

MICHAEL M. SHARA, DEBRA J. WALLACE, AND DAVID R. ZUREK

Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218

AND

ANTHONY F. J. MOFFAT

De� partement de Physique, Universite� de Montre� al, C.P. 6128, Succursale Centre-Ville, Montre� al, QC H3C 3J7, Canada ;and Observatoire du Mont Me� gantic

Received 1997 July 31 ; revised 1998 January 21

ABSTRACTHubble Space Telescope (HST ) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet

stars WR 146 and WR 147, as well as the visual binary WR 86, resolve each of them into two very0A.2close optical components. The colors of these optical pairs are similar, indicating that they are likely tobe physically bound WR] OB systems at the same distance. Comparison of the locations of the opticalcomponents of WR 146 and WR 147 with high-resolution radio maps strikingly demonstrates that thenonthermal radio components arise between the optical binary components, closer to the OB componentthan the WR. This is as expected if the nonthermal radio emission results from the collision of the stellarwinds of the binary components seen in the HST images. The similar magnitudes and colors determinedfor the components of WR 86 from our HST images, combined with an analysis of the unresolved, com-bined WC7] OB optical spectrum, indicates an absolute magnitude for the WC7 component of aboutM

VD [5.

Key words : binaries : visual È stars : individual (WR 86, WR 146, WR 147) È stars : Wolf-Rayet

1. INTRODUCTION

The fraction of binary systems, and their role in the for-mation and evolution of stars with Wolf-Rayet (WR) typespectra, still appears to be controversial. Estimates of thefrequency of binary WR stars range from 40% to 50% (e.g.,

& Conti et al. to 80%Vanbeveren 1980 ; Mo†at 1986)& Sarazin Furthermore,(Vanbeveren 1995 ; Dalton 1995).

close binary interactions in systems with massive and lumi-nous components are still not well understood. In particu-lar, strong modiÐcations of a binaryÏs equipotential surfacesdue to radiation pressure and powerful winds, make evolu-tionary predictions very difficult (see & NiemelaZorec

et al. and references therein).1980a, 1980b ; Drechsel 1995,In fact, wind collisions may strongly hinder any kind ofmass transfer, allowing all but the very closest systems toevolve as two separate single stars of the same type (e.g.,Mo†at 1995 ; Kondo 1996).

The close companions of WR stars are usually of O type,as revealed by the presence of central (as opposed to blue-shifted P Cygni) H, He I, and He II absorption lines super-posed on WR emission lines. If the WR ] O pair is suffi-ciently close, antiphased radial velocity (RV) variations ofthe WR emission and O absorption lines are observed.However, many WR stars have absorption lines in theirspectra but lack detectable RV variations (e.g., et al.Mo†at

ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ1 Based on observations with the NASA/ESA Hubble Space Telescope,

obtained at the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555.

2 Member of Carrera del Investigador, CIC, Prov•� ncia Buenos Aires,Argentina. Visiting Astronomer, CTIO, NOAO, operated by AURA, Inc.,for the National Science Foundation.

The simplest explanation for this is an O-type com-1986).panion with a period exceeding the timescale over which thespectral observations were made, usually several years. Thisin turn implies separations exceeding a few AU. At a dis-tance of 2 kpc (a common distance for many of the closestWR stars), a few AU translates into angular separations onthe order of a milliarcsecond, which are normally unre-solvable with ground-based telescopes. Only very widebinaries (with separations exceeding B1000 AU) can beroutinely discovered as visual pairs with ground-basedobservations. Any real understanding of WR binaries andtheir frequency of occurrence demands observations that““ Ðll the gap ÏÏ between visual and spectroscopic binariesknown from ground-based observations. Toward that endwe are carrying out a systematic imaging survey of GalacticWR stars with the corrected Wide Field Planetary Camera(WFPC2) of the Hubble Space Telescope (HST ). As bothWR stars and OB stars belong to the most massive popu-lation having the bluest intrinsic colors, in an HR diagram avisual WR ] OB binary should appear as two stars withsimilar UBV colors.

Full details on the scope of our survey, methodology, andresults will be given elsewhere. Here we report signiÐcantobservational results on three targets : WR 86 (\HD156327), WR 146, and WR 147 (WR numbers are from thecatalog of der Hucht et al.van 1981).

The Galactic WR stars WR 146 and WR 147 are bothknown to be double radio sources with thermal and non-thermal components. The thermal components of the radiosources have been identiÐed with WR wind emission. Thenonthermal emission has been assumed to come from aregion of wind collision between the WR star and a putativeluminous companion (cf. et al. and refer-Dougherty 1996,ences therein). In the case of WR 146, of spectral type WC6

2047

2048 NIEMELA ET AL. Vol. 115

TABLE 1

JOURNAL OF OBSERVATIONS

Total Exposure TimeObject Date Filter (s)

WR 86 . . . . . . . 1996 Jun 2 F555W 0.60WR 86 . . . . . . . 1996 Jun 2 F439W 1.2WR 86 . . . . . . . 1996 Jun 2 F336W 2.8WR 146 . . . . . . 1996 Feb 17 F555W 1.6WR 146 . . . . . . 1996 Feb 17 F439W 50.0WR 146 . . . . . . 1996 Feb 17 F336W 400.0WR 147 . . . . . . 1996 Feb 22 F555W 20.0WR 147 . . . . . . 1996 Feb 22 F439W 160.0

& Mendoza Shara, & Mo†at(Herbig 1960 ; Smith, 1990),et observed Hc and Hd absorption linesDougherty al.

superposed on the WR emissions. These absorptions wereattributed to an OB-type companion to the WR star. ForWR 147, of spectral type WN8(h) Shara, & Mo†at(Smith,

observations of the Ðeld with speckle interferometry1996),et al. and a high-resolution optical CCD(Lortet 1987)

imaging et al. failed to yield any evidence for(Moran 1989)a visual companion. However, in a recent paper etWilliamsal. report the detection of a stellar companion to WR(1997)147 that is about 3 mag fainter in a K-band infrared image.Because of its proximity (d \ 630 pc), WR 147Ïs thermalwind is well resolved and is seen to be highly clumped in theradio. Whether the time-averaged radio wind has a bipolarstructure or not (e.g., due to stochastic clump-(Davis 1994)ing in a spherical wind) remains to be seen. In both WR 146and WR 147, the nonthermal radio source is observed to beextended in a direction roughly perpendicular to the linejoining the two sources et al. et(Churchwell 1992 ; Williamsal. et al. as expected for a wind-1997 ; Dougherty 1996),collision shock cone seen in projection.

It is important to determine the emission mechanism ofthe nonthermal components observed in high spatialresolution radio images. Since the observations of radiocontinuum emission do not carry information on the radialdistance where the emission is produced, the nonthermalsources could in principle be background objects, as alsopointed out for WR 147 by et al. ThereforeWilliams (1997).observations in other wavelengths are necessary to decide iftwo adjacent sources also are at the same distance and not amere projection e†ect. If the nonthermal radiation arisesfrom the interaction of stellar winds, high-resolution opticalimages should show visual companions to the WR starsslightly beyond the extended nonthermal structures in adirection opposite to the WR star. Here we present high-resolution HST WFPC2 images of WR 146 and WR 147,which resolve both stars as very close visual binaries withsimilar colors, and indeed conÐrm the colliding-wind originfor the nonthermal radio components. We also discuss thepossible spectral types of the companions as derived fromtheir broadband colors.

We also present HST images for the WR ] OB visualbinary system WR 86, which conÐrm and improve uponprevious ground-based observations, by resolving this starinto two components of similar magnitude. An analysis ofthe optical spectrum of WR 86 indicates that the OB com-panion is more luminous than a main sequence star, for itsspectral type. The magnitudes and colors of our HSTimages of WR 86 allow us to estimate the visual absolutemagnitude of the WC7 component.

Our observations are summarized in In we° 2. ° 3present the results and discussion of our observations : theresolved optical images of WR 146 and WR 147 comparedwith previously known radio observations ; and the param-eters of the components of the binary systems. Section 4brieÑy summarizes our results.

2. OBSERVATIONS

CCD images of the Ðelds of WR 86, WR 146, and WR 147were obtained with the Wide Field Planetary Camera 2 ofthe Hubble Space Telescope in 1996 through the F336W,F439W, and F555W Ðlters. These closely approximate theJohnson UBV Ðlters. Therefore, we will call magnitudesobserved with HST Ðlters as UBV , although their match tothe Johnson system is only approximate. Details of theobservations are given in Table 1.

The HST images were pipeline processed (HST DataHandbook, 1995) and combined using the tasks CRREJand COMBINE in STSDAS/IRAF. Photometry of thestars was carried out with DAOPHOT/IRAF (Stetson

The magnitudes were corrected for zero point using1987).the HST o†set to Vega (HST Data Handbook, 1995).

2.1. PhotometrySince WR 86 and WR 146 have very close companions,

the contaminations in the photometry from the wings of thecompanion star is nonnegligible. It was therefore decided touse point-spread function (PSF) photometry (cf. Stetson

for best results, even for WR 147, whose companion is1987)distant. However, there are no suitable stars on the WR0A.6

frames from which to build a reliable PSF. We thusretrieved images (with the same gain and Ðlters) from theHST archive that had a sufficient number of stars to con-struct a good PSF. The images were scaled to a 1 s expo-sure, and a PSF for each Ðlter was constructed. This PSF,with FWHM of about 1.51^ 0.04 pixels for all Ðlters, or

was then used on the three WR stars (WR 86, WR0A.0675,146, and WR 147), after scaling their exposures also to 1 s,to provide precise photometry and relative positions for theWR stars and their companions.

3. RESULTS AND DISCUSSION

3.1. HST ImagesGray-scale plots of the HST images of WR 86, WR 146,

and WR 147 are presented in showing that allFigure 1,three WR stars appear as visual binaries in the high spatialresolution optical HST images. The separation (r) and posi-tion angles (P.A.) of the binaries, as well as the componentstarsÏ magnitudes and colors, are listed in Table 2.

3.2. Comparison with High-Resolution Radio MapsIn the case of WR 147, accurate astrometry of the Ðeld as

determined by reference to 35 stars in the Heidelberg PPMCatalogue & Bastian has shown that the(Ro� ser 1988)thermal radio source is coincident with the WR star towithin et al. As the nonthermal source is0A.2 (Moran 1989).

away, the identity of the WR star with the thermal0A.6source seems secure.

Assuming that the WR star is also coincident with thethermal source in the WR 146 radio binary, we show in

the locations of the visual binary components asFigure 2seen in the HST images, superposed on the high

No. 5, 1998 OPTICAL COMPANIONS OF WR 86, WR 146, AND WR 147 2049

FIG. 1.ÈGray-scale plots of HST Planetary Camera images of WR 86, WR 146, and WR 147, showing the binary nature of these stars

resolution radio maps. In this Ðgure the nonthermal radiosources are seen to lie between the optical binary com-ponents. strikingly demonstrates that the opticalFigure 2companions to the WR stars appear located just asexpected if the nonthermal radio component arises from thecollision of the winds of two luminous stars.

3.3. T he W R 146 Binary System and BD ]40¡4243WR 146 is a highly reddened star located at the periphery

of the Cygnus OB2 stellar association (cf. der Hucht etvanal. From ground-based observations, WR 146 is1981).known to have a brighter close visual companion, BD]40¡4243 \ WR 146C, located 9A to the southeast (cf.Cohen et al. 1975). Previous photographic UBV photo-

metry of this Ðeld has been made by Lawrence, &Reddish,Pratt BD ]40¡4243 and WR 146 appear in their(1967).catalog of stars in the region of the Cygnus OB2 associationas stars 1165 and 1166, respectively.

It is interesting to note that the visually brighter star ofthe optical close pair seen in the ground-based obser-vations, BD ]40¡4243, has a B[V color that is consider-ably less red than that of WR 146. From the B[V andU[B colors of the brighter star we infer that it may be areddened star of late B spectral type. The visual magnitudeand colors of BD ]40¡4243 appear quite similar to thosedetermined for stars in front of the Cygnus OB2 associationby & Thompson Thus BD ]40¡4243 seemsMassey (1991).to be closer than this association.

TABLE 2

ASTROMETRY AND PHOTOMETRY

r P.A. V B[V U[BObject (mas) (deg) (mag) (mag) (mag)

WR 86A . . . . . . . 10.18^ 0.09 0.50 ^ 0.14 [0.20^ 0.16WR 86B . . . . . . . 286^ 39 109 ^ 9 10.20^ 0.09 0.53 ^ 0.13 [0.55^ 0.16WR 146A . . . . . . 13.64^ 0.04 2.70 ^ 0.06 0.83 ^ 0.09WR 146B . . . . . . 168^ 31 21 ^ 4 13.88^ 0.04 2.44 ^ 0.06 0.60 ^ 0.09WR 146C . . . . . . 11.36^ 0.05 1.01 ^ 0.18 0.65 ^ 0.27WR 147A . . . . . . 13.86^ 0.06 4.06 ^ 0.14WR 147B . . . . . . 643^ 157 350 ^ 2 16.02^ 0.06 4.09 ^ 0.28

NOTE.ÈStar A is always the brighter in the close pairs. Star WR 146C \ BD ]40¡4243 is thebright companion about 9A southeast from WR 146A.

2050 NIEMELA ET AL. Vol. 115

FIG. 2.ÈLocation of the visual binary components of WR 146 (left), and WR 147 (right), superposed on high-resolution radio maps published byet al. and et al. respectively.Dougherty (1996) Williams (1997),

We have also measured the UBV magnitudes of BD]40¡4243 in our HST frames, and they are included in

A comparison of these values with the photogra-Table 2.phic values of et al. shows similar colors, butReddish (1967)the HST results yield a slightly fainter V magnitude. This isprobably due to the difficulty of separating the pair BD]40¡4243 and WR 146 on photographic plates.

WR 146 has been previously assumed to be a member ofthe Cygnus OB2 stellar association (e.g., &HerbigMendoza However, the membership has been ques-1960).tioned by the recent estimate of the distance to WR 146determined by et al. From infrared pho-Dougherty (1996).tometry, et estimate a distance of 1.2 ^ 0.3Dougherty al.kpc for WR 146, which would locate this system somewhatcloser than the distance of 1.7 ^ 0.2 kpc (e.g., &MasseyThompson of Cygnus OB2.1991)

However, the close neighbor of WR 146 at 9A, BD]40¡4243, appears to be substantially less reddened than isthe Cyg OB2 association. WR 146, on the other hand, hasmuch larger reddening than the minimum(E

B~VD 3.0)

reddening necessary for membership in the(EB~V

D 1.2)Cygnus OB2 association by & This isMassey Thompson.compatible with WR 146 belonging to this association.

Our HST observations clearly resolve WR 146 into twocomponents of similar magnitude and color (A and B ; see

This implies that the northern component is also anFig. 1).intrinsically blue star with reddening similar to that of theWR component, as expected if the stars are physicallyrelated.

The reddening-independent color factor Q &(JohnsonMorgan for both components of WR 146 determined1953)from our HST data are similar, further supporting our con-clusion that the stars have similar reddening and are at the

same distance from the Sun. The Q-factor appears morenegative than usually observed for O-type stars, e.g., Table5 in & Thompson This might be due toMassey (1991).errors in the U-band magnitudes of our snapshot images orcontribution of the emission lines to the broadband colorsof the WR component. However, it is more likely a problemof lack of calibration of the UBV system for such highlyreddened stars & Vogt Therefore, the intrin-(Mo†at 1977).sic colors of the binary components are not well constrainedfrom our data. On the other hand, the relative magnitudesand colors of the southern and northern components of WR146 in our HST images (see can be compared withTable 2)the broadband UBV photometry of the(Feinstein 1964)single WC6 star WR 23 (\HD 92809), a member of theCarina OB1 association & Stenholm(Lundstro� m 1984).Adopting the for WR 23 et al. andE

b~v\ 0.34 (Smith 1990)

the relation & StenholmEB~V

/Eb~v

\ 1.21 (Lundstro� myields for WR 23 for normal reddening1984) M

V\ [4.8

and distance modulus of 12.5 mag for Carina OB1 (Massey& Johnson If the WC6 star in WR 146 has similar1993).

then the northern OB component hasMV, M

V\[4.6,

which corresponds to an O8ÈO9 type star (see Humphreys& McElroy which is in good agreement with O8.5 V1984),estimated by et al.Willis (1997).

This is also in keeping with the fact that the stellar windshock front seen as the nonthermal radio component islocated much closer to the northern component (see Fig. 2),as would be expected from the collision of the more power-ful wind of a WC6 star with that of an O8ÈO9 V typecompanion. However, at the distance of the Cygnus OB2association, and adopting mag followingA

V\ 8.0

et al. both components of the WR 146Dougherty (1996),binary would have This is brighter than theM

VD[5.5.

No. 5, 1998 OPTICAL COMPANIONS OF WR 86, WR 146, AND WR 147 2051

value quoted above for the WC6 type star WR23, andwould mean that the OB component of WR 146 is a brightgiant/supergiant or is of earlier O spectral type (see below).

3.4. T he W R 147 Binary SystemEven more reddened than WR 146, WR 147 is seen

toward the same Galactic longitude as the Cygnus OB2association, but below the Galactic plane. From near-infrared photometry, the distance of WR 147 was estimatedby et al. to be 630^ 70 pc, which wouldChurchwell (1992)make it the second nearest WR star after the c Vel system.

Our HST images show two stars separated by 0A.6 (Fig.In this case, the southern component, known to be the1).

WN8 star, is about 2 mag brighter than the northern com-panion. Taking into account the high luminosity assignedfor WN8 type stars which becomes(M

vD [6.7, M

VD

der Hucht et al. the northern component[6.8 ; van 1988),of WR 147 would have With this value ofM

VD [4.7.

absolute visual magnitude, and colors similar to thesouthern component, it could be an O8ÈO9 VÈIII or anearly B-type star.

et al. in their recent IR photometry ofWilliams (1997)WR 147 system Ðnd the OB member to be about 3 magfainter and that its K magnitude is consistent with a B0.5 Vstar. The fact we Ðnd the northern component in opticalwavelengths to be only 2 mag fainter, may indicate anearlier spectral type than B0.5 V, or that the star(s) in theWR 147 system have variable magnitude(s). This last possi-bility may also account for the nondetection of the OBcomponent by speckle interferometry et al.(Lortet 1987).

The fact that WR 147 is the Ðrst WN8-type star known ina visual binary system, makes it very important to deter-mine an accurate spectral type of the companion from spec-troscopy, in order to directly determine the absolutemagnitude of the WR component.

As in the case of WR 146, our HST photometry shows(see that the binary components of WR 147 haveTable 2)almost equal colors, pointing to similar reddening asexpected if the visual binary components are physicallyrelated.

shows that the wind collision zone observed asFigure 2the nonthermal radio source is again located much nearerto the northern component. This implies that the northernbinary component has a weaker wind than the WN8 star, aswould be the case for a late O-or early B-type star.

3.5. W R 86\ HD 156327This star has long been known to be a visual binary

system of only separation et al. recently0A.2 (Je†ers 1963),conÐrmed by speckle interferometry et al.(Hartkopf 1993).WR 86 is classiÐed as WC7] abs in the catalog of dervanHucht et al. Previously, the OB component had been(1981).classiÐed as B0 V WR 86 is also assumed to be(Smith 1968).the exciting source of the H II region S10 &(GeorgelinGeorgelin 1970).

Our HST images of WR 86 clearly show two stars ofquite similar magnitude, one being again somewhat bluerthan the other (see A gray-scale plot of the WR 86Table 2).system is included in The similarity of the magni-Figure 1.tudes of the components of WR 86 in our HST imageso†ers an opportunity to estimate the absolute magnitude ofthe WC7 component, provided that the spectral type of theOB component is known. To this end, we have digitizedphotographic optical spectra of WR 86 obtained in May

1980 with the image tube spectrograph attached to the 1 mYale telescope at Cerro Tololo Interamerican Observatory,Chile.

The blue image-tube spectrum of WR 86 is shown inwhere absorption lines from the OB companionFigure 3,

are also identiÐed. A comparison of the spectrum in Figurewith the digital spectral atlas of OB stars &3 (Walborn

Fitzpatrick obtained with the same telescope and1990),similar instrumental conÐguration as our spectra of WR 86,indicates a spectral type close to B0, but evidently moreluminous than a main-sequence star. Because of the super-position of the WC7 spectrum, a comparison of absorption-line ratios is difficult, but the mere detection of Si IV, Si III,and O II lines points to a luminosity class between III and I,which, for equal magnitudes of the two stars, indicates avisual absolute magnitude of at least as bright as about [5(therefore normal) for the WC7 component (cf. Humphreys& McElroy 1984).

3.6. Comparison of W R 146 and W R 147 with the CollidingW inds Model

Our HST images allow us to compare the relative windmomentum Ñuxes (mass-loss rate ] terminal velocity) ofthe WR ] OB binary components in the framework of thecolliding wind theory & Usov Since the(Eichler 1993).binaries here have very large absolute separations, thewinds must be colliding at terminal speed. The ratio of thewind momentum Ñuxes g is related to the distance alongr0the line joining the two stars of the contact discontinuity,considered as the wind collision zone coinciding with thenonthermal radio source, from the star with the weakerwind, in this case the OB component, and the separation Dof both binary components, by

g1@2 \ r0/(D[ r0) .

From our HST images, and the high-resolution radiomaps, we can measure projected values of and D, esti-r0mated as 42 and 168 mas for WR 146, and 92 and 643 masfor WR 147. With these values we determine the ratio ofwind momentum Ñuxes of the components in both systemssince the projection factor cancels out in the ratio. For theWR 146 system we obtain g D 0.10, and for the WR 147system g D 0.028. We note in particular that the value for

FIG. 3.ÈBlue optical spectrum of WR 86. The absorption lines identi-Ðed are Hc, Hd, He I jj4009, 4026, 4121, 4144, 4168, 4387, 4471 ; Si IV

jj4089, 4116 ; Si III jj4552È4568 ; O II jj4075, 4350 (blend), 4366, 4415È4417 ; 4590È4596.

2052 NIEMELA ET AL.

the ratio of the wind momentum Ñuxes of the componentsin the WR 146 binary system is rather high. Taking for theWR component WR 146A a terminal velocity of 2900 kms~1 & Williams and a mass-loss rate(Eenens 1994) (M0 )equal to the upper limit (due to our larger distance)3.0] 10~5 yr~1 obtained by et al.M

_Dougherty (1996),

the value of g D 0.10 for the components of WR 146 meansthat the OB component of the system also must possess aconsiderable mass loss rate and terminal velocity. Since theterminal velocities of O-type stars are of the same order ofmagnitude as those of WR stars (e.g., Barlow, &Prinja,Howarth but the mass loss rates of O-type stars are1990),at least 1 order of magnitude lower (see &ChlebowskiGarmany only a combination of these quantities cor-1991),responding to stars of early O or Of type, not to stars of lateO main-sequence type, will reproduce g D 0.10. Taking intoaccount the similar visual magnitudes of both components,the spectral type of the OB component in WR 146 may beO6ÈO5 VÈIII.

The value of g D 0.028 in the WR 147 system means thatthe wind momentum Ñux of the OB component is less than3% of that from the WN8 star. The terminal velocity of1000 km s~1 and the mass-loss rate of 4.6 ] 10~5M0 M

_yr~1 for the WN8 component in WR 147 et al.(Williamssuggest that the OB component has a wind momen-1997)

tum Ñux roughly corresponding with spectral type sug-gested by our observations, namely, O8ÈO9 VÈIII (e.g.,

& Prinja et al.Howarth 1989 ; Prinja 1990).

4. SUMMARY

We brieÑy summarize our results as follows :

1. Images obtained with the Hubble Space Telescoperesolve each of the radio binaries WR 146 and WR 147, aswell as WR 86, into two close, optical components.

2. The colors and magnitudes of the close binary com-ponents indicate that they are physically related WR ] OBpairs.

3. The components of WR 86 have quite similar magni-tudes in our HST images, thus a new determination of thespectral type of the OB component from optical spectra asB0 IIIÈI allows an estimate of for the WC7 com-M

V[[5

ponent.4. The OB components in WR 146 and WR 147 are

located just beyond the nonthermal radio sources, asexpected if the nonthermal emission arises near the bowshock head of the colliding winds from the WR star and itsOB companion.

5. A comparison of our data for WR 146 with a model ofcolliding stellar winds suggests that the OB component inthe WR 146 binary has a large mass-loss rate and terminalvelocity.

6. At a distance of 1.7 kpc, the projected separation of theWR 146 binary components is D285 AU; at the distance of630 pc, the separation of the WR 147 binary components isD404 AU. These indicate binary periods of several hundredyears.

M. M. S. acknowledges support in the form of HST grantGO-5482. A. F. J. M. is grateful for Ðnancial aid fromNSERC (Canada) FCAR (Que� bec). V. S. N. is grateful forthe use of CTIO facilities and acknowledges FundacionAntorchas, Argentina, for a travel grant.

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