HD 159176: photospheric and wind-dominated light-curve analyses coupled to wind modelling

Pachoulakis, Ioannis

doi:10.1093/mnras/280.1.153

Cited by 10 publications

(11 citation statements)

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“…Since the stars (and winds) are identical the winds should collide at the system centre of mass, half‐way between the stars. The collision should be radiative, even if the mass‐loss rates are an order of magnitude lower than the values quoted in Pachoulakis (1996). The XMM–Newton observation was taken just after quadrature, corresponding to phases 0.28–0.41 (or, alternatively, phases 0.78–0.91) in our models (note that the phase reported in De Becker et al is 0.53–0.66, but in their paper phase 0.0 corresponds to the maximum radial velocity of the primary component).…”

Section: Comparison To Observationsmentioning

confidence: 85%

3D models of radiatively driven colliding winds in massive O + O star binaries - III. Thermal X-ray emission

Pittard

Parkin

2010

Monthly Notices of the Royal Astronomical Society

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The X-ray emission from the wind-wind collision in short-period massive O + O star binaries is investigated. The emission is calculated from 3D hydrodynamical models which incorporate gravity, the driving of the winds, orbital motion of the stars and radiative cooling of the shocked plasma. Changes in the amount of stellar occultation and circumstellar attenuation introduce phase-dependent X-ray variability in systems with circular orbits, while strong variations in the intrinsic emission also occur in systems with eccentric orbits. The X-ray emission in eccentric systems can display strong hysteresis, with the emission softer after periastron than at corresponding orbital phases prior to periastron, reflecting the physical state of the shocked plasma at these times.Our simulated X-ray light curves bear many similarities to observed light curves. In systems with circular orbits the light curves show two minima per orbit, which are identical (although not symmetric) if the winds are identical. The maxima in the light curves are produced near quadrature, with a phase delay introduced due to the aberration and curvature of the wind collision region. Circular systems with unequal winds produce minima of different depths and duration. In systems with eccentric orbits the maxima in the light curves may show a very sharp peak (depending on the orientation of the observer), followed by a precipitous drop due to absorption and/or cooling. We show that the rise to maximum does not necessarily follow a 1/d sep law. Our models further demonstrate that the effective circumstellar column can be highly energy dependent. Therefore, spectral fits which assume energy-independent column(s) are overly simplified and may compromise the interpretation of observed data.To better understand observational analyses of such systems we apply Chandra and Suzaku response files, plus Poisson noise, to the spectra calculated from our simulations and fit these using standard XSPEC models. We find that the recovered temperatures from two-or threetemperature mekal fits are comparable to those from fits to the emission from real systems with similar stellar and orbital parameters/nature. We also find that when the global abundance is thawed in the spectral fits, subsolar values are exclusively returned, despite the calculations using solar values as input. This highlights the problem of fitting oversimplified models to data, and of course is of wider significance than just the work presented here.Further insight into the nature of the stellar winds and the wind-wind collision region in particular systems will require dedicated hydrodynamical modelling, the results of which will follow in due course.

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Section: Comparison To Observationsmentioning

confidence: 85%

3D models of radiatively driven colliding winds in massive O + O star binaries - III. Thermal X-ray emission

Pittard

Parkin

2010

Monthly Notices of the Royal Astronomical Society

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“…Although Pachoulakis (1996) inferred only slightly different wind momenta (see Table 1 values ofṀ (9 × 10 −7 and 1 × 10 −7 M yr −1 ) when passed through the relation of Vink et al (2001). Such large differences inṀ, and hence wind strength, are however at odds with the essentially equal spectral types inferred from optical spectroscopy.…”

Section: Unequal Windsmentioning

confidence: 90%

“…Analysing UV resonance line profiles of HD 159176 as observed with IUE, Pachoulakis (1996) derived a mass-loss rate of about 3 × 10 −6 M yr −1 for each star (note that this value is Table 1. Relevant parameters of the HD 159176 binary system adopted throughout this paper unless otherwise stated.…”

Section: Introductionmentioning

confidence: 99%

AnXMM-Newtonobservation of the massive binary HD 159176

Becker

Rauw

Pittard

et al. 2004

A&A

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Abstract.We report the analysis of an XMM-Newton observation of the close binary HD 159176 (O7 V + O7 V). The observed L X /L bol ratio reveals an X-ray luminosity exceeding by a factor ∼7 the expected value for X-ray emission from single O-stars, therefore suggesting a wind-wind interaction scenario. EPIC and RGS spectra are fitted consistently with a two temperature mekal optically thin thermal plasma model, with temperatures ranging from ∼2 to 6× 10 6 K. At first sight, these rather low temperatures are consistent with the expectations for a close binary system where the winds collide well before reaching their terminal velocities. We also investigate the variability of the X-ray light curve of HD 159176 on various short time scales. No significant variability is found and we conclude that if hydrodynamical instabilities exist in the wind interaction region of HD 159176, they are not sufficient to produce an observable signature in the X-ray emission. Hydrodynamic simulations using wind parameters from the literature reveal some puzzling discrepancies. The most striking one concerns the predicted X-ray luminosity which is one or more orders of magnitude larger than the observed one. A significant reduction of the mass loss rate of the components compared to the values quoted in the literature alleviates the discrepancy but is not sufficient to fully account for the observed luminosity. Because hydrodynamical models are best for the adiabatic case whereas the colliding winds in HD 159176 are most likely highly radiative, a totally new approach has been envisaged, using a geometrical steady-state colliding wind model suitable for the case of radiative winds. This model successfully reproduces the spectral shape of the EPIC spectrum, but further developments are still needed to alleviate the disagreement between theoretical and observed X-ray luminosities.

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“…• of Pachoulakis (1996), which indicates that the system is probably in co-rotation. The fits of the radial velocity curve with the eccentricity as a free parameter gave e = 0.02, with no improvement of the residuals, and the circularisation time calculated from Tassoul (1990) is shorter than 57 000 years.…”

Section: Orbital Solutionmentioning

confidence: 97%

“…Their mass ratio is very close to 1, which means equal spectral types for both components. On the other hand, Pachoulakis (1996) studied HD 159 176 with UV, optical and photometric data and found that the primary star is actually hotter than the secondary star and has thus an earlier type, suggesting an O6 V + O7 V binary. An XMM-Newton study of HD 159 176 revealed an excess of Xray luminosity by a factor ∼7 compared to the expected value for a single O-star (De ), which indicates the presence of a wind-wind interaction in the system.…”

Section: Hd 159 176mentioning

confidence: 99%

The Struve-Sahade effect in the optical spectra of O-type binaries

Linder¹,

Rauw²,

Sana

et al. 2007

A&A

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Aims. We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the StruveSahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding). Methods. We use high resolution optical spectra to determine new orbital solutions and spectral types of HD 165 052, HD 100 213, HD 159 176 and DH Cep. As good knowledge of the fundamental parameters of the considered systems is necessary to examine the Struve-Sahade effect. We then study equivalent width variations in the lines of both components of these binaries during their orbital cycle.Results. In the case of these four systems, variations appear in the equivalent widths of some lines during the orbital cycle, but the definition given above can any longer be valid, since it is now clear that the effect modifies the primary spectrum as much as the secondary spectrum. Furthermore, the lines affected, and the way in which they are affected, depend on the considered system. For at least two of them (HD 100 213 and HD 159 176) these variations probably reflect the ellipsoidal variable nature of the system.

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HD 159176: photospheric and wind-dominated light-curve analyses coupled to wind modelling

Cited by 10 publications

References 0 publications

3D models of radiatively driven colliding winds in massive O + O star binaries - III. Thermal X-ray emission

3D models of radiatively driven colliding winds in massive O + O star binaries - III. Thermal X-ray emission

AnXMM-Newtonobservation of the massive binary HD 159176

The Struve-Sahade effect in the optical spectra of O-type binaries

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