Nonlinear Evolution of the Radiation-Driven Magneto-Acoustic Instability

Fernández, Rodrigo; Socrates, Aristotle

doi:10.1088/0004-637x/767/2/144

Cited by 5 publications

(3 citation statements)

References 40 publications

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“…8, in addition to HD 93129A and ζ Pup -that clumping begins very close to the photosphere. It is possible for the LDI to produce clumping without also producing significant X-ray emission if the shocks are not strong enough to heat the wind plasma to more than 10 6 K. It is also quite possible that the clumping in O stars begins already in the photosphere, perhaps due to the radiationdriven magneto-acoustic instability (Fernandez & Socrates 2013). Future simulations will have to address these issues of clump formation and X-ray production in the context of the LDI.…”

Section: Discussionmentioning

confidence: 99%

Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive

Cohen

Wollman

Leutenegger

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We quantitatively investigate the extent of wind absorption signatures in the X-ray grating spectra of all non-magnetic, effectively single O stars in the Chandra archive via line profile fitting. Under the usual assumption of a spherically symmetric wind with embedded shocks, we confirm previous claims that some objects show little or no wind absorption. However, many other objects do show asymmetric and blue shifted line profiles, indicative of wind absorption. For these stars, we are able to derive wind mass-loss rates from the ensemble of line profiles, and find values lower by an average factor of 3 than those predicted by current theoretical models, and consistent with Hα if clumping factors of f cl ≈ 20 are assumed. The same profile fitting indicates an onset radius of X-rays typically at r ≈ 1.5 R * , and terminal velocities for the X-ray emitting wind component that are consistent with that of the bulk wind. We explore the likelihood that the stars in the sample that do not show significant wind absorption signatures in their line profiles have at least some X-ray emission that arises from colliding wind shocks with a close binary companion. The one clear exception is ζ Oph, a weak-wind star that appears to simply have a very low mass-loss rate. We also reanalyse the results from the canonical O supergiant ζ Pup, using a solarmetallicity wind opacity model and findṀ = 1.8 × 10 −6 M ⊙ yr −1 , consistent with recent multi-wavelength determinations.2 Effectively single in the sense that there is no obvious windwind interaction-related X-ray emission.

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Section: Discussionmentioning

confidence: 99%

Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive

Cohen

Wollman

Leutenegger

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…For a realistic case of an Eddington-limb-darkened source, Sundqvist & Owocki (2015) find that this nodal type topology causes strong variabilities in the wind that extend down to the photosphere. Moreover, any variability at the inner boundary (e.g., bright spots (Ramiaramanantsoa et al 2018), g-modes, or radiation-driven magneto-acoustic waves (Fernández & Socrates 2013;Sen et al 2018)) would add to this variability and potentially cause shock structures to appear quickly after the wind leaves the surface.…”

Section: Introductionmentioning

confidence: 99%

Testing the reliability of X-rays as a tool for constraining mass-loss rates of hot stars

Gunderson

Gayley

Pradhan

et al. 2022

Monthly Notices of the Royal Astronomical Society

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We fit a new line shape model to Chandra X-ray spectra of the O supergiant ζ Puppis to investigate the spatial distribution of embedded shocks in the wind. Our goal is to track the hot gas by replacing the common assumption that it is proportional to the cool gas emission measure. Instead of assuming a turn-on radius for the hot gas (as appropriate for the line-deshadowing instability internal to the wind), we parametrize the hot gas in terms of a mean-free path for accelerated low-density gas to encounter slower high-density material. We find that this alternative model is equally successful as previous approaches at fitting X-ray spectral lines in the 5 – 17 Å wavelength range. The wind properties described by our model are consistent with the literature, while providing new insights into the spatial heating distribution of the shocked gas. We find that the characteristic radii where the hottest gas appears is inversely proportional to line formation temperature, suggesting that stronger shocks appear generally closer to the surface. This picture is more consistent with pockets of low-density, rapid acceleration at the lower boundary than with an internally generated wind instability. We also find that the overall wind mass-loss rates, which we infer from the profile shapes using our heating model, are broadly consistent with prior results, showing that X-ray spectra provide a means of inferring wind mass-loss rates that is robust with respect to changes in the specific heating picture used.

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“…Even before this linear behavior was understood, Begelman (2001) analytically predicted that the nonlinear development of the instability in the rapid diffusion regime would result in trains of shock waves, and this was confirmed in detail by radiation MHD simulations of Turner et al (2005). The rapid diffusion limit of the instability can even exist in regimes where gas pressure is comparable to radiation pressure or magnetic pressure (Blaes & Socrates 2003), and its nonlinear outcome has been simulated by Fernández & Socrates (2013).…”

Section: Introductionmentioning

confidence: 91%

Radiative MHD Simulations of Photon Bubbles in Radiation-Supported Magnetized Atmospheres of Neutron Stars with Isotropic Thomson Scattering

Zhang,

Blaes,

Jiang

2021

Preprint

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A major uncertainty in the structure and dynamics of magnetized, radiation pressure dominated neutron star accretion columns in X-ray pulsars and pulsating ultraluminous X-ray sources is that they are thought to be subject to the photon bubble instability. We present the results of two dimensional radiation relativistic magnetohydrodynamic simulations of a non-accreting, static atmosphere to study the development of this instability assuming isotropic Thomson scattering in the slow diffusion regime that is relevant to neutron star accretion columns. Photon bubbles generally grow faster toward shorter wavelengths, until a maximum growth rate is achieved at the radiation viscosity length scale, which is generally quite small and requires high numerical resolution to simulate. We confirm the consistency between our simulation results and linear theory in detail, and show that the nonlinear evolution inevitably leads to collapse of the atmosphere with the higher resolution simulation collapsing faster due to the presence of shorter length scale nonlinear structures. At least in static atmospheres with horizontally periodic boundary conditions, this resolution dependence may make simulations of the nonlinear dynamics of photon bubble instability in neutron star accretion columns challenging. It remains to be seen whether these difficulties will persist upon inclusion of an accretion flow through the top and magnetically-confined horizontal boundaries through which photons can escape. Our results here provide a foundation for such future work.

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Nonlinear Evolution of the Radiation-Driven Magneto-Acoustic Instability

Cited by 5 publications

References 40 publications

Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive

Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive

Testing the reliability of X-rays as a tool for constraining mass-loss rates of hot stars

Radiative MHD Simulations of Photon Bubbles in Radiation-Supported Magnetized Atmospheres of Neutron Stars with Isotropic Thomson Scattering

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