Monte Carlo simulations of polarimetric and light variability from corotating interaction regions in hot stellar winds

Carlos-Leblanc, Danny; St-Louis, N.; Bjorkman, J. E.; Ignace, Richard

doi:10.1093/mnras/stz2273

Cited by 7 publications

(3 citation statements)

References 27 publications

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“…These are assumed to arise in an aspherical stellar wind or in active zones near the stellar photosphere of a rotating single star. As the perturbations propagate outward, they form a spiral density structure that is embedded in the WR wind (Carlos-Leblanc et al 2019). Qualitatively, this spiral structure may be analogous that that which arises from a wind-wind collision and its trailing shock region that propagates outward (Parkin & Pittard 2008;Parkin et al 2009).…”

Section: Epoch To Epoch Variationsmentioning

confidence: 96%

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

Koenigsberger,

Schmutz

2020

Preprint

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Context: EZ Canis Majoris is a classical Wolf-Rayet star whose binary nature has been debated for decades. It was recently modeled as an eccentric binary with a periodic brightening at periastron of the emission originating in a shock heated zone near the companion. Aims: The focus of this paper is to further test the binary model and to constrain the nature of the unseen close companion by searching for emission arising in the shock-heated region. Methods: We analyze over 400 high resolution the International Ultraviolet Explorer spectra obtained between 1983 and 1995 and XMM-Newton observations obtained in 2010. The light curve and radial velocity (RV) variations were fit with the eccentric binary model and the orbital elements were constrained. Results: We find RV variations in the primary emission lines with a semi-amplitude K 1 ∼30 km s −1 in 1992 and 1995, and a second set of emissions with an anti-phase RV curve with K 2 ∼150 km s −1 . The simultaneous model fit to the RVs and the light curve yields the orbital elements for each epoch. Adopting a Wolf-Rayet mass M 1 ∼20 M leads to M 2 ∼3-5 M , which implies that the companion could be a late B-type star. The eccentric (e=0.1) binary model also explains the hard X-ray light curve obtained by XMM-Newton and the fit to these data indicates that the duration of maximum is shorter than the typical exposure times. Conclusions: The anti-phase RV variations of two emission components and the simultaneous fit to the RVs and the light curve are concrete evidence in favor of the binary nature of EZ Canis Majoris. The assumption that the emission from the shock-heated region closely traces the orbit of the companion is less certain, although it is feasible because the companion is significantly heated by the WR radiation field and impacted by the WR wind.

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Section: Epoch To Epoch Variationsmentioning

confidence: 96%

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

Koenigsberger,

Schmutz

2020

Preprint

View full text Add to dashboard Cite

show abstract

“…These are assumed to arise in an aspherical stellar wind or in active zones near the stellar photosphere of a rotating single star. As the perturbations propagate outward, they form a spiral density structure that is embedded in the WR wind (Carlos-Leblanc et al 2019). Qualitatively, this spiral structure may be analogous to that which arises from a wind-wind collision and its trailing shock region that propagates outward (Parkin & Pittard 2008;Parkin et al 2009).…”

Section: Cirs Wind-wind Collisions and Periastron Effectsmentioning

confidence: 98%

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

Koenigsberger

Schmutz

2020

A&A

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Context. EZ Canis Majoris is a classical Wolf-Rayet star whose binary nature has been debated for decades. It was recently modeled as an eccentric binary with a periodic brightening at periastron of the emission originating in a shock heated zone near the companion. Aims. The focus of this paper is to further test the binary model and to constrain the nature of the unseen close companion by searching for emission arising in the shock-heated region. Methods. We analyze over 400 high resolution International Ultraviolet Explorer spectra obtained between 1983 and 1995 and XMM-Newton observations obtained in 2010. The light curve and radial velocity (RV) variations were fit with the eccentric binary model and the orbital elements were constrained. Results. We find RV variations in the primary emission lines with a semi-amplitude K1 ∼ 30 km s−1 in 1992 and 1995, and a second set of emissions with an anti-phase RV curve with K2 ∼ 150 km s−1. The simultaneous model fit to the RVs and the light curve yields the orbital elements for each epoch. Adopting a Wolf-Rayet mass M1 ∼ 20 M⊙ leads to M2 ∼ 3−5 M⊙, which implies that the companion could be a late B-type star. The eccentric (e = 0.1) binary model also explains the hard X-ray light curve obtained by XMM-Newton and the fit to these data indicates that the duration of maximum is shorter than the typical exposure times. Conclusions: The anti-phase RV variations of two emission components and the simultaneous fit to the RVs and the light curve are concrete evidence in favor of the binary nature of EZ Canis Majoris. The assumption that the emission from the shock-heated region closely traces the orbit of the companion is less certain, although it is feasible because the companion is significantly heated by the WR radiation field and impacted by the WR wind.

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“…The polarization does not only depend on the inclination or rotational velocity, but it also depends on the opacity of the medium. In our model, we assumed the optical thin regime, but using Monte Carlo radiative transfer, Carlos-Leblanc et al (2019) show that the polarization increases by increasing the optical depth (τ > 1). Due to their high mass loss rate, WR stars have an optical thick wind even to the electron scattering.…”

Section: Optical Depthmentioning

confidence: 99%

Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind

Abdellaoui

Krtička

Kurfürst

2022

A&A

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Context. Fast rotating Wolf-Rayet stars are expected to be progenitors of long duration gamma-ray bursts. However, the observational test of this model is problematic. Spectral lines of Wolf-Rayet stars originate in expanding stellar wind, therefore a reliable spectroscopical determination of their rotational velocities is difficult. Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind may provide an indirect way to determine the rotational velocities of these stars. However, detailed wind models are required for this purpose. Aims. We determine the intrinsic polarization of Wolf-Rayet stars from hydrodynamical wind models as a function of rotational velocity. Methods. We used 2.5D hydrodynamical simulations to calculate the structure of rotating winds of Wolf-Rayet stars. The simulations account for the deformation of the stellar surface due to rotation, gravity darkening, and nonradial forces. From the derived models, we calculated the intrinsic stellar polarization. The mass loss rate was scaled to take realistic wind densities of Wolf-Rayet stars into account. Results. The hydrodynamical wind models predict a prolate wind structure, which leads to a relatively low level of polarization. Even relatively large rotational velocities are allowed by observational constrains. The obtained wind structure is similar to that obtained previously for rotating optically thin winds. Conclusions. Derived upper limits of rotational velocities of studied Wolf-Rayet stars are not in conflict with the model of long duration gamma-ray bursts.

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Monte Carlo simulations of polarimetric and light variability from corotating interaction regions in hot stellar winds

Cited by 7 publications

References 27 publications

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind

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