The 2.35 year itch of Cygnus OB2 #9

Nazé, Yaël; Mahy, L.; Damerdji, Y.; Kobulnicky, Henry A.; Pittard, J. M.; Parkin, E. R.; Absil, Olivier; Blomme, R.

doi:10.1051/0004-6361/201219442

Cited by 57 publications

(92 citation statements)

References 46 publications

(66 reference statements)

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“…Unlike what is seen in some other long-period interacting wind O + O binaries (e.g. Cyg OB2 #9, Nazé et al 2012b), the high-energy tail does not reveal a strong Fe K line near 6.7 keV. At phases φ = 0.946 and φ = 0.055, there are indications of such a line in the EPIC-pn spectra, which have the highest S/N ratio over this energy band, although only at a rather low level.…”

Section: Spectral Fittingmentioning

confidence: 57%

“…How such a process affects the Fe xxv line emission remains to be seen. If this scenario is correct, an obvious question that comes to mind is why we observe strong deviations from the 1/r relation in 9 Sgr but not in Cyg OB2 #9 (Nazé et al 2012b), which is also a prominent non-thermal radio emitter. A detailed modelling of these systems as done by Pittard & Dougherty (2006) for WR 140 would certainly shed new light onto the problem, but such a study is beyond the scope of the present paper.…”

Section: Discussionmentioning

confidence: 91%

“…A spectacular illustration of such a 1/r X-ray flux variation is the O5-5.5 I + O3-4 III system Cyg OB2 #9, which has a period of 2.36 yr and an eccentricity of e = 0.7 (Nazé et al 2012b). …”

Section: Discussionmentioning

confidence: 99%

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Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Rauw

Blomme

Nazé

et al. 2016

A&A

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Context. The long-period, highly eccentric O-star binary 9 Sgr, known for its non-thermal radio emission and its relatively bright X-ray emission, went through its periastron in 2013. Aims. Such an event can be used to observationally test the predictions of the theory of colliding stellar winds over a broad range of wavelengths. Methods. We conducted a multi-wavelength monitoring campaign of 9 Sgr around the 2013 periastron. In this paper, we focus on X-ray observations and optical spectroscopy. Results. The optical spectra allow us to revisit the orbital solution of 9 Sgr and to refine its orbital period to 9.1 years. The X-ray flux is maximum at periastron over all energy bands, but with clear differences as a function of energy. The largest variations are observed at energies above 2 keV, whilst the spectrum in the soft band (0.5−1.0 keV) remains mostly unchanged, indicating that it arises far from the collision region, in the inner winds of the individual components. The level of the hard emission at periastron clearly deviates from the 1/r relation expected for an adiabatic wind-interaction zone, whilst this relation seems to hold at the other phases that are covered by our observations. The spectra taken at phase 0.946 reveal a clear Fe xxv line at 6.7 keV, but no such line is detected at periastron (φ = 0.000), although a simple model predicts a strong line that should be easily visible in the data. Conclusions. The peculiarities of the X-ray spectrum of 9 Sgr could reflect the effect of radiative inhibition as well as a phasedependent efficiency of particle acceleration on the shock properties.

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Section: Spectral Fittingmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 91%

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Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

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Blomme

Nazé

et al. 2016

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“…Indeed, the orbital solution derived by Nazé et al (2010) returned e ∼ 0.744. This has since been revised to e 0.711, with an orbital period of 860 days, using the recent optical and radio analysis by Nazé et al (2012b) and Blomme et al (2013). The model constructed by Nazé et al (2012b; based on estimates for the stellar parameters) provides valuable physical insight into the system, particularly the anticipated significance of wind acceleration on the importance of radiative cooling.…”

Section: Cyg Ob2#9mentioning

confidence: 99%

“…Dougherty & Williams 2000;van Loo 2005;De Becker et al 2006;van Loo et al 2006van Loo et al , 2008De Becker 2007;Nazé et al 2008;Montes et al 2009;Blomme et al 2010;A&A 570, A10 (2014) A prime example that fits into this class of X-ray and nonthermal radio emitting massive binary is the O+O-star system Cyg OB2#9 (van Loo et al 2008;Nazé et al 2008Nazé et al , 2010Volpi et al 2011). Our recent campaign to study this object has so far consisted of an analysis of optical and X-ray data by Nazé et al (2012b), and radio observations by Blomme et al (2013), which have refined the orbital solution and provided initial estimates for the stellar parameters − see Tables 1 and 2. The variation of the X-ray flux with orbital phase correlates with the inverse of binary separation (i.e.…”

Section: Introductionmentioning

confidence: 99%

The 2.35 year itch of Cygnus OB2 #9

Parkin

Pittard

Nazé

et al. 2014

A&A

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Context. The wind-wind collision in a massive star binary system leads to the generation of high temperature shocks that emit at X-ray wavelengths and, if particle acceleration is effective, may exhibit non-thermal radio emission. Cyg OB2#9 is one of a small number of massive star binary systems in this class. Aims. X-ray and radio data recently acquired as part of a project to study Cyg OB2#9 are used to constrain physical models of the binary system, providing in-depth knowledge about the wind-wind collision and the thermal, and non-thermal, emission arising from the shocks. Methods. We use a 3D, adaptive mesh refinement simulation (including wind acceleration, radiative cooling, and the orbital motion of the stars) to model the gas dynamics of the wind-wind collision. The simulation output is used as the basis for radiative transfer calculations considering the thermal X-ray emission and the thermal/non-thermal radio emission. Results. The flow dynamics in the simulation show that wind acceleration (between the stars) is inhibited at all orbital phases by the opposing star's radiation field, reducing pre-shock velocities below terminal velocities. To obtain good agreement with the X-ray observations, our initial mass-loss rate estimates require a down-shift by a factor of ∼7.7 to 6.5 × 10 −7 M yr −1 and 7.5 × 10 −7 M yr −1 for the primary and secondary star, respectively. Furthermore, the low gas densities and high shock velocities in Cyg OB2 #9 are suggestive of unequal electron and ion temperatures, and the X-ray analysis indicates that an immediately post-shock electron-ion temperature ratio of 0.1 is also required. The radio emission is dominated by non-thermal synchrotron emission. A parameter space exploration provides evidence against models assuming equipartition between magnetic and relativistic energy densities. However, fits of comparable quality can be attained with models having stark contrasts in the ratio of magnetic-to-relativistic energy densities. Both X-ray and radio lightcurves are largely insensitive to viewing angle. The variations in X-ray emission with orbital phase can be traced back to an inverse relation with binary separation and pre-shock velocity. The radio emission also scales with pre-shock velocity and binary separation, but to positive powers (i.e. not inversely). The radio models also reveal a subtle effect whereby inverse Compton cooling leads to an increase in emissivity as a result of the synchrotron characteristic frequency being significantly reduced. Finally, using the results of the radio analysis, we estimate the surface magnetic field strengths to be ≈0.3−52 G.

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Perspectives for observing hot massive stars with XMM‐Newton in the years 2017–2027

Rauw

2017

Astron Nachr

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XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects helped us gain a deeper insight into the physics of single massive stars with or without magnetic fields, as well as of massive binary systems, where the stellar winds of both stars interact. These observations also revealed a number of previously unexpected features that challenge our understanding of the dynamics of the stellar winds of massive stars. I briefly summarize the results obtained over the past 15 years and highlight the perspectives for the next decade. It is anticipated that coordinated (X-ray and optical or UV) monitoring and time-critical observations of either single or binary massive stars will become the most important topics in this field over the coming years. Synergies with existing or forthcoming X-ray observatories (NuStar, Swift, eROSITA) will also play a major role and will further enhance the importance of XMM-Newton in our quest for understanding the physics of hot, massive stars.

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The 2.35 year itch of Cygnus OB2 #9

Cited by 57 publications

References 46 publications

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

The 2.35 year itch of Cygnus OB2 #9

Perspectives for observing hot massive stars with XMM‐Newton in the years 2017–2027

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