Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary<i>γ</i><sup>2</sup> Velorum

Schild, Hans H.; Güdel, M.; Mewe, R.; Schmutz, W.; Raassen, A. J. J.; Audard, M.; Dumm, T.; Hucht, K. A. van der; Leutenegger, Maurice A.; Skinner, Stephen L.

doi:10.1051/0004-6361:20047035

Cited by 60 publications

(96 citation statements)

References 54 publications

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“…At this particular phase, the line of sight to the observer essentially goes through the O wind and unveils the X-ray emitting wind interaction zone that is much more absorbed at other phases due to the intervening dense WR wind. This result has been confirmed and further refined by more recent observations and models (Schild et al 2004;Henley et al 2005).…”

Section: Introductionsupporting

confidence: 79%

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

Gosset¹,

Nazé²,

Sana

et al. 2009

A&A

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Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O system of the Carina region, a system well known for the high mass of its primary. Methods. Phase-resolved X-ray observations of the massive WR+O binary system WR 22 were performed with the XMM-Newton facility. We observed the object at seven different phases from near apastron to near periastron. Results. The X-ray spectrum can be represented by a two-component, optically thin, thermal plasma model with a first one at a typical temperature of 0.6 keV and a second hotter one in the range 2.0-4.5 keV. The hot component is indicative of a colliding wind phenomenon, but its flux is remarkably constant with time despite the high eccentricity of the orbit. Although surprising at first, this actually does not contradict the results of the hydrodynamical simulations of the wind collision that we performed. When the system goes from apastron to periastron, the soft part of the X-ray flux is progressively lowered by an increasing intervening absorbing column. This behaviour can be interpreted in terms of an X-ray emitting plasma located near the O star, but not fully intrinsic to it, and accompanying the star when it dives into the wind of the WR component. A model is presented that interprets most of the observational constraints. This model suggests that the mass-loss rate ofṀ WR ∼ 1.6 × 10 −5 M yr −1 assumed for the WR could still be slightly too high, whereas it is already lower than other published values. From the comparison of the observed and the expected absorptions at phases near periastron, we deduce that the hard X-ray emitting collision zone should at least have a typical size of 50-60 R , but that the size for the soft X-ray emitting region could reach 244 R if the assumed mass-loss rate is correct. We also present an upper limit to the X-ray luminosity of the WR component that further questions the existence of intrinsic X-ray emission from single WN stars.

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Section: Introductionsupporting

confidence: 79%

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

Gosset¹,

Nazé²,

Sana

et al. 2009

A&A

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“…While X-ray variability as a function of orbital phase has been observed in WR11 (e.g. Schild et al 2004) that system is observed at higher inclination, such that significant orbital variation in the wind properties and hence line of sight extinction are present, which would be absent for the putative low inclination configuration proposed here. Consequently, one can at least qualitatively understand the X-ray properties of W239, although quantitative confirmation would require a tailored hydrodynamical simulation, which currently appears unwarranted given the lack of observational constraints.…”

Section: The Nature Of the W239 Systemmentioning

confidence: 49%

A VLT/FLAMES survey for massive binaries in Westerlund 1

Clark

Ritchie

Negueruela

et al. 2011

A&A

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Context. There is growing evidence that a treatment of binarity amongst OB stars is essential for a full theory of stellar evolution. However the binary properties of massive stars -frequency, mass ratio & orbital separation -are still poorly constrained. Aims. In order to address this shortcoming we have undertaken a multiepoch spectroscopic study of the stellar population of the young massive cluster Westerlund 1. In this paper we present an investigation into the nature of the dusty Wolf-Rayet star and candidate binary W239. Methods. To accomplish this we have utilised our spectroscopic data in conjunction with multi-year optical and near-IR photometric observations in order to search for binary signatures. Comparison of these data to synthetic non-LTE model atmosphere spectra were used to derive the fundamental properties of the WC9 primary. Results. We found W239 to have an orbital period of only ∼5.05 days, making it one of the most compact WC binaries yet identified. Analysis of the long term near-IR lightcurve reveals a significant flare between 2004-6. We interpret this as evidence for a third massive stellar component in the system in a long period (>6 yr), eccentric orbit, with dust production occuring at periastron leading to the flare. The presence of a near-IR excess characteristic of hot (∼1300 K) dust at every epoch is consistent with the expectation that the subset of persistent dust forming WC stars are short (<1 yr) period binaries, although confirmation will require further observations. Non-LTE model atmosphere analysis of the spectrum reveals the physical properties of the WC9 component to be fully consistent with other Galactic examples. Conclusions. The simultaneous presence of both short period Wolf-Rayet binaries and cool hypergiants within Wd 1 provides compelling evidence for a bifurcation in the post-Main Sequence evolution of massive stars due to binarity. Short period O+OB binaries will evolve directly to the Wolf-Rayet phase, either due to an episode of binary mediated mass loss -likely via case A mass transfer or a contact configuration -or via chemically homogenous evolution. Conversely, long period binaries and single stars will instead undergo a red loop across the HR diagram via a cool hypergiant phase. Future analysis of the full spectroscopic dataset for Wd 1 will constrain the proportion of massive stars experiencing each pathway; hence quantifying the importance of binarity in massive stellar evolution up to and beyond supernova and the resultant production of relativistic remnants.

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“…Indeed, practical examples of this multicolumn behaviour have been reported on several occasions, e.g. in γ 2 Vel (Schild et al 2004) but also in another context in γ Cas (Smith et al 2004). …”

Section: Notesmentioning

confidence: 85%

“…An additional possible X-ray source is present in the massive binary systems where the winds of the two components are colliding (Stevens et al 1992). This phenomenon is also present in WR+O binaries (see for WC+O, γ 2 Vel, Willis et al 1995;Stevens et al 1996;Schild et al 2004;WR 140, Pollock et al 2005;Zhekov & Skinner 2000;and for WN+O, V444 Cyg, Maeda et al 1999;WR 22, Gosset et al 2009;WR 25, Pollock & Corcoran 2006;Gosset 2007 andFig. 29 of Güdel &Nazé 2009;WR147, Pittard et al 2002;Zhekov & Park 2010).…”

Section: Introductionmentioning

confidence: 85%

XMM-Newtonobservation of the enigmatic object WR 46

Gosset

Becker

Nazé

et al. 2011

A&A

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Aims. To further investigate the nature of the enigmatic object WR 46 and better understand the X-ray emission in massive stars and in their evolved descendants, we observed this variable object for more than two of its supposed cycles. The X-ray emission characteristics are appropriate indicators of the difference between a genuine Wolf-Rayet star and a specimen of a super soft source as sometimes suggested in the literature. The X-ray emission analysis might contribute to understanding the origin of the emitting plasma (intrinsically shocked wind, magnetically confined wind, colliding winds, and accretion onto a white dwarf or a more compact object) and to substantiating the decision about the exact nature of the star. Methods. The X-ray observations of WR 46 were performed with the XMM-Newton facility over an effective exposure time of about 70 ks.Results. Both the X-ray luminosity of WR 46, typical of a Wolf-Rayet star, and the existence of a relatively hard component (including the Fe-K line) rule out the possibility that WR 46 could be classified as a super soft source, and instead favour the Wolf-Rayet hypothesis. The X-ray emission of the star turns out to be variable below 0.5 keV but constant at higher energies. The soft variability is associated to the Wolf-Rayet wind, but revealing its deep origin necessitates additional investigations. It is the first time that such a variability is reported for a Wolf-Rayet star. Indeed, the X-ray emission exhibits a single-wave variation with a typical timescale of 7.9 h which could be related to the period observed in the visible domain both in radial velocities (single-wave) and in photometry (double-wave). The global X-ray emission seems to be dominated by lines and is closely reproduced by a three-temperature, optically thin, thermal plasma model. The derived values are 0.1−0.2 keV, 0.6 keV, and ∼4 keV, which indicates that a wide range of temperatures is actually present. The soft emission part could be related to a shocked-wind phenomenon. The hard tail of the spectrum cannot presently be explained by such an intrinsic phenomenon as a shocked wind and instead suggests there is a wind-wind collision zone, as does the relatively high L X /L bol ratio. We argue that this scenario implies the existence of an object farther away from the WN3 object than any possible companion in an orbit related to the short periodicity.

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Wind clumping and the wind-wind collision zone in the Wolf-Rayet binaryγ² Velorum

Cited by 60 publications

References 54 publications

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

A VLT/FLAMES survey for massive binaries in Westerlund 1

XMM-Newtonobservation of the enigmatic object WR 46

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Wind clumping and the wind-wind collision zone in the Wolf-Rayet binaryγ2 Velorum

Cited by 60 publications

References 54 publications

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

A VLT/FLAMES survey for massive binaries in Westerlund 1

XMM-Newtonobservation of the enigmatic object WR 46

Contact Info

Product

Resources

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Wind clumping and the wind-wind collision zone in the Wolf-Rayet binaryγ² Velorum