The Wind‐Wind Collision Region of the Wolf‐Rayet Binary V444 Cygni: How Much Optical Line Emission Does It Produce?

We present results from a study of the eclipsing, colliding-wind binary V444 Cyg that uses a combination of X-ray and optical spectropolarimetric methods to describe the 3D nature of the shock and wind structure within the system. We have created the most complete X-ray light curve of V444 Cyg to date using 40 ks of new data from Swift, and 200 ks of new and archived XMM-Newton observations. In addition, we have characterized the intrinsic, polarimetric phase-dependent behavior of the strongest optical emission lines using data obtained with the University of Wisconsin's Half-Wave Spectropolarimeter. We have detected evidence of the Coriolis distortion of the wind-wind collision in the X-ray regime, which manifests itself through asymmetric behavior around the eclipses in the system's X-ray light curves. The large opening angle of the X-ray emitting region, as well as its location (i.e. the WN wind does not collide with the O star, but rather its wind) are evidence of radiative braking/inhibition occurring within the system. Additionally, the polarimetric results show evidence of the cavity the wind-wind collision region carves out of the Wolf-Rayet star's wind.

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“…However, our larger value agrees with several other observational estimates. Flores et al (2001) found a similar shock half-opening angle of 70…”

mentioning

confidence: 76%

“…Photospheric absorption in the O star is an important source of line profile variations observed in total light (Marchenko et al 1997;Flores et al 2001). If we do not correct for this unpolarized absorption we risk removing too much continuum polarization from our observations.…”

Section: Optical Polarimetrymentioning

confidence: 99%

V444 Cygni X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region

Lomax

Nazé

Hoffman

et al. 2014

A&A

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“…As discussed in Flores, et al (2001), these collisions produce profile distortions within emission lines that vary with orbital phase. This has been shown to cause up to a ∼12% change in the equivalent width of prominent emissions lines in V444 Cyg, a WR + O binary system (Flores et al 2001). Additionally, as shown by Foellmi et al (2008) for HD 5980 (a WR/LBV binary), these wind-wind collisions increase centroid-measurement error since the emission lines become asymmetric as the orbital cycle changes.…”

Section: Identifying the Binariesmentioning

confidence: 97%

The Close Binary Frequency of Wolf-Rayet Stars as a Function of Metallicity in M31 and M33

Neugent

Massey

2014

ApJ

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Massive star evolutionary models generally predict the correct ratio of WCtype and WN-type Wolf-Rayet stars at low metallicities, but underestimate the ratio at higher (solar and above) metallicities. One possible explanation for this failure is perhaps single-star models are not sufficient and Roche-lobe overflow in close binaries is necessary to produce the "extra" WC stars at higher metallicities. However, this would require the frequency of close massive binaries to be metallicity dependent. Here we test this hypothesis by searching for close Wolf-Rayet binaries in the high metallicity environments of M31 and the center of M33 as well as in the lower metallicity environments of the middle and outer regions of M33. After identifying ∼100 Wolf-Rayet binaries based on radial velocity variations, we conclude that the close binary frequency of Wolf-Rayets is not metallicity dependent and thus other factors must be responsible for the overabundance of WC stars at high metallicities. However, our initial identifications and observations of these close binaries have already been put to good use as we are currently observing additional epochs for eventual orbit and mass determinations.

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“…Hirv et al (2006), Marchenko, Moffat & Koenigsberger (1994), Underhill, Yang &Hill (1988), andMünch (1950) determined system parameters and made evaluations regarding WR wind based on the intensities and radial velocity changes of the He II (λλ 4686, 5412Å), and N V (λλ 4945, 4603Å) lines. Flores et al (2001), Auer & Koenigsberger (1994), Shore & Brown (1988), Underhill & Fahey (1987), Koenigsberger & Auer (1985), Eaton, Cherepashchuk & Khaliullin (1985), and Kuhi (1968) studied the phase dependence of line profiles in optical and UV range spectrograms and discussed the physical properties of the WR wind as well as the effects of the wind-wind collision. Wind-wind collision effects were also discussed by Luo, McCray & Mac Low (1990), Usov (1990), Corcoran et al (1993), Maeda et al (1999), Bhatt et al (2010) and Fauchez et al (2011) who studied the X-ray light curve and X-ray spectra of V444 Cyg.…”

Section: Introductionmentioning

confidence: 99%

A 2007 photometric study and UV spectral analysis of the Wolf‐Rayet binary V444 Cyg

Eriş

Ekmekci

2011

Astron Nachr

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Photometric and spectroscopic characteristics of the WN5+O6 binary system, V444 Cyg, were studied. The WilsonDevinney (WD) analysis, using new BV observations carried out at the Ankara University Observatory, revealed the masses, radii, and temperatures of the components of the system as MWR = 10.64 M , MO = 24.68 M , RWR = 7.19 R , RO = 6.85 R , TWR = 31 000 K, and TO = 40 000 K , respectively. It was found that both components had a full spherical geometry, whereas the circumstellar envelope of the WR component had an asymmetric structure.The O − C analysis of the system revealed a period lengthening of 0.139 ± 0.018 s yr −1 , implying a mass loss rate of (6.76 ± 0.39) × 10 −6 M yr −1 for the WR component. Moreover, 106 IUE-NEWSIPS spectra were obtained from NASA's IUE archive for line identification and determination of line profile variability with phase, wind velocities and variability in continuum fluxes. The integrated continuum flux level (between 1200-2000Å) showed a mild and regular increase from orbital phase 0.00 up to 0.50 and then a decrease in the same way back to phase 0.00. This is evaluated as the O component making a constant and regular contribution to the system's UV light as the dominant source. The C IV line, originating in the circumstellar envelope, had the highest velocity while N IV line, originating in deeper layers of the envelope, had the lowest velocity. The average radial velocity calculated by using the C IV line (wind velocity) was found as 2326 km s −1 .

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The Wind‐Wind Collision Region of the Wolf‐Rayet Binary V444 Cygni: How Much Optical Line Emission Does It Produce?

Cited by 12 publications

References 22 publications

V444 Cygni X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region

V444 Cygni X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region

The Close Binary Frequency of Wolf-Rayet Stars as a Function of Metallicity in M31 and M33

A 2007 photometric study and UV spectral analysis of the Wolf‐Rayet binary V444 Cyg

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