Bow shock nebulae of hot massive stars in a magnetized medium

Meyer, Dominique M.-A.; Mignone, A.; Kuiper, Rolf; Raga, A. C.; Kley, W.

doi:10.1093/mnras/stw2537

Cited by 58 publications

(84 citation statements)

References 141 publications

(159 reference statements)

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“…Likewise, high values of the rotation measure follow the surface of the bow shock in the central plane, leading to parabolic shapes. This is consistent with the results of different approaches, such as the 3D HD models by Mohamed et al (2012) or the 2D MHD models by Meyer et al (2017), the latter of which also gives similar maps of their axisymmetric model at different inclination angles.…”

Section: Discussionsupporting

confidence: 90%

Skymaps of observables of three-dimensional magnetohydrodynamic astrosphere models

Baalmann

Scherer

Fichtner

et al. 2020

A&A

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Context. Three-dimensional models of astrospheres have recently become of interest. However, comparisons between these models and observations are non-trivial because of the two-dimensional nature of observations. Aims. By projecting selected physical values of three-dimensional models of astrospheres onto the surface of a sphere that is centred on a virtual all-sky observer, these models can be compared to observational data in different observables: the column density, bremsstrahlung flux, rotation measure, Hα flux, and synchrotron or cyclotron flux. Methods. Projections were calculated by rotating and moving the astrosphere model to the desired position and orientation and by then computing the value of a given patch on the sphere by a modified line-of-sight integration. Contributions to the selected observable made by all model cells that are connected to the patch by the line of sight in question were taken into account.Results. When the model produces a bow shock, a distinct parabolic structure produced by the outer astrosheath can be seen in every observable of the projection, the exact shape depending on the orientations of the line of sight and the stellar motion. Of all four examined astrosphere models, only that of λ Cephei shows fluxes that are higher than current observational thresholds. This is due to the strong stellar wind and interstellar inflow of the λ Cephei model.

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Section: Discussionsupporting

confidence: 90%

Skymaps of observables of three-dimensional magnetohydrodynamic astrosphere models

Baalmann

Scherer

Fichtner

et al. 2020

A&A

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“…Hydrodynamical simulations of OB star bowshocks show that density ratios may reach factors of 10 over small scales that are well below the observational resolution limits. Factors of four are about right when averaged over ≃0.1-0.3 pc scales typical of sample objects (e.g., Figures 7 and 4, respectively, of Comeron & Kaper 1998;Meyer et al 2017).…”

Section: Introductionmentioning

confidence: 94%

Mass-loss Rates for O and Early B Stars Powering Bow Shock Nebulae: Evidence for Bistability Behavior

Kobulnicky¹,

Chick²,

Povich³

2019

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Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bowshock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bowshocks nebulae, 67 are OB stars. The median peculiar velocity is 11 km s −1 , significantly smaller than classical "runaway star" velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from ≃10 −7 M ⊙ yr −1 for mid-O dwarfs to 10 −9 M ⊙ yr −1 for late-O dwarfs-a factor of about 2.7 lower than the often-used Vink et al. (2001) formulation. Our results provide the first observational mass-loss rates for B0-B3 dwarfs and giants-10 −9 to 10 −8 M ⊙ yr −1 . We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bi-stability phenomenon in the range T eff =19,000-27,000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical windluminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.

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“…An object with a strong wind, moving into dense ambient medium at such high speed, will necessarily produce a strong bow shock. The physics of bow shocks in front of fast-moving OB stars is also a well-studied problem (e.g., Wilkin 1996;Comeron & Kaper 1998;Meyer et al 2017), based on the same physical elements as the colliding wind problem (forward shock into the WR wind; contact discontinuity; reverse shock into the ULX wind). Near the apex of the bow shock, the WR wind is mov-ing perpendicularly to the shock, but the forward shock is driven by the supersonic orbital motion of the BH, which, in the case of CG X-1, is only slightly lower than the WR wind speed.…”

Section: Colliding Winds and Bow Shockmentioning

confidence: 99%

CG X-1: An Eclipsing Wolf–Rayet ULX in the Circinus Galaxy

Qiu

Soria

Wang

et al. 2019

ApJ

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We investigated the time-variability and spectral properties of the eclipsing X-ray source Circinus Galaxy X-1 (GG X-1), using Chandra, XMM-Newton and ROSAT. We phase-connected the lightcurves observed over 20 years, and obtained a best-fitting period P = (25, 970.0±0.1) s ≈7.2 hr, and a period derivativeṖ /P = (10.2±4.6)×10 −7 yr −1 . The X-ray lightcurve shows asymmetric eclipses, with sharp ingresses and slow, irregular egresses. The eclipse profile and duration vary substantially from cycle to cycle. We show that the X-ray spectra are consistent with a power-law-like component, absorbed by neutral and ionized Compton-thin material, and by a Compton-thick, partial-covering medium, responsible for the irregular dips. The high X-ray/optical flux ratio rules out the possibility that CG X-1 is a foreground Cataclysmic Variable; in agreement with previous studies, we conclude that it is the first example of a compact ultraluminous X-ray source fed by a Wolf-Rayet star or stripped Helium star. Its unocculted luminosity varies between ≈4 ×10 39 erg s −1 and ≈3 ×10 40 erg s −1 . Both the donor star and the super-Eddington compact object drive powerful outflows: we suggest that the occulting clouds are produced in the wind-wind collision region and in the bow shock in front of the compact object. Among the rare sample of Wolf-Rayet X-ray binaries, CG X-1 is an exceptional target for studies of super-critical accretion and close binary evolution; it is also a likely progenitor of gravitational wave events.

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Bow shock nebulae of hot massive stars in a magnetized medium

Cited by 58 publications

References 141 publications

Skymaps of observables of three-dimensional magnetohydrodynamic astrosphere models

Skymaps of observables of three-dimensional magnetohydrodynamic astrosphere models

Mass-loss Rates for O and Early B Stars Powering Bow Shock Nebulae: Evidence for Bistability Behavior

CG X-1: An Eclipsing Wolf–Rayet ULX in the Circinus Galaxy

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