Accretion Power in Astrophysics

Frank, J.; King, Andrew; Raine, Derek

doi:10.1017/cbo9781139164245

Cited by 2,313 publications

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“…Chap. 6 in Frank et al 2002). A similar situation occurs when the disc is truncated by a magnetic field.…”

Section: Inner Boundary Conditionmentioning

confidence: 77%

Dwarf nova outbursts in intermediate polars

Hameury

Lasota

2017

A&A

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Context. The disc instability model (DIM) has been very successful in explaining the dwarf nova outbursts observed in cataclysmic variables. When, as in intermediate polars, the accreting white dwarf is magnetised, the disc is truncated at the magnetospheric radius, but for mass-transfer rates corresponding to the thermal-viscous instability such systems should still exhibit dwarf-nova outbursts. Yet, the majority of intermediate polars, in which the magnetic field is not large enough to completely disrupt the accretion disc, seem to be stable, and the rare observed outbursts, in particular in systems with long orbital periods, are much shorter than normal dwarf-nova outbursts. Aims. We investigate the predictions of the disc instability model for intermediate polars in order to determine which of the observed properties of these systems can be explained by the DIM. Methods. We use our numerical code for the time evolution of accretion discs, modified to include the effects of the magnetic field, with constant or variable mass transfer from the secondary star. Results. We show that intermediate polars have mass transfer low enough and magnetic fields large enough to keep the accretion disc stable on the cold equilibrium branch. We show that the infrequent and short outbursts observed in long-period systems, such as, for example, TV Col, cannot be attributed to the thermal-viscous instability of the accretion disc, but instead have to be triggered by an enhanced mass-transfer from the secondary, or, more likely, by some instability coupling the white dwarf magnetic field with that generated by the magnetorotational instability operating in the accretion disc. Longer outbursts (a few days) could result from the disc instability.

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“…Chap. 6 in Frank et al 2002). A similar situation occurs when the disc is truncated by a magnetic field.…”

Section: Inner Boundary Conditionmentioning

confidence: 77%

Dwarf nova outbursts in intermediate polars

Hameury

Lasota

2017

A&A

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“…In the case of the conical flow (Abramowicz & Zurek 1981) one prescribes, H = Dr, where D is a simple constant of proportionality. While these two cases could be viewed as giving an explicit dependence of H on r, another well-invoked, but much more complicated prescription in accretion literature is that of the disc with the condition of hydrostatic equilibrium imposed in the vertical direction (Matsumoto et al 1984;Frank et al 2002). In this particular instance, the function H in Eq.…”

Section: The Equations Of the Flow And Its Fixed Pointsmentioning

confidence: 99%

“…In this particular instance, the function H in Eq. (2) will be determined according to the way P has been prescribed (Frank et al 2002). In all of these cases, however, it is a common practice to standardise transonicity in the flow by scaling its bulk velocity with the help of the local speed of sound, which is given as cs = (∂P/∂ρ) 1/2 .…”

Section: The Equations Of the Flow And Its Fixed Pointsmentioning

confidence: 99%

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The role of flow geometry in influencing the stability criteria for low angular momentum axisymmetric black hole accretion

et al. 2012

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Using mathematical formalism borrowed from dynamical systems theory, a complete analytical investigation of the critical behaviour of the stationary flow configuration for the low angular momentum axisymmetric black hole accretion provides valuable insights about the nature of the phase trajectories corresponding to the transonic accretion in the steady state, without taking recourse to the explicit numerical solution commonly performed in the literature to study the multi-transonic black hole accretion disc and related astrophysical phenomena. Investigation of the accretion flow around a non rotating black hole under the influence of various pseudo-Schwarzschild potentials and forming different geometric configurations of the flow structure manifests that the general profile of the parameter space divisions describing the multi-critical accretion is roughly equivalent for various flow geometries. However, a mere variation of the polytropic index of the flow cannot map a critical solution from one flow geometry to the another, since the numerical domain of the parameter space responsible to produce multi-critical accretion does not undergo a continuous transformation in multi-dimensional parameter space. The stationary configuration used to demonstrate the aforementioned findings is shown to be stable under linear perturbation for all kind of flow geometries, black hole potentials, and the corresponding equations of state used to obtain the critical transonic solutions. Finally, the structure of the acoustic metric corresponding to the propagation of the linear perturbation studied are discussed for various flow geometries used.

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“…Instead of dumping material directly onto the compact star, the primary Roche lobe is slowly filled with a near Keplerian disc. Angular momentum needs to be dispersed within this accretion disc in order to allow gas to spiral inwards towards the compact star [7].…”

Section: Accretion Discs and Angular Momentummentioning

confidence: 99%

Spiral Waves in Accretion Discs— Observations

Steeghs

2001

Astrotomography

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Abstract. I review the observational evidence for spiral structure in the accretion discs of cataclysmic variables (CVs). Doppler tomography is ideally suited to resolve and map such co-rotating patterns and allows a straightforward comparison with theory. The dwarf nova IP Pegasi presents the best studied case, carrying two spiral arms in a wide range of emission lines throughout its outbursts. Both arms appear at the locations where tidally driven spiral waves are expected, with the arm closest to the gas stream weaker in the lines compared to the arm closest to the companion. Eclipse data indicates sub-Keplerian velocities in the outer disc. The dramatic disc structure changes in dwarf novae on timescales of days to weeks, provide unique opportunities for our understanding of angular momentum transport and the role of density waves on the structure of accretion discs. I present an extension to the Doppler tomography technique that relaxes one of the basic assumptions of tomography, and is able to map modulated emission sources. This extension allows us to fit anisotropic emission from, for example, spiral shocks, the irradiated companion star and disc-stream interaction sites.

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Accretion Power in Astrophysics

Cited by 2,313 publications

References 0 publications

Dwarf nova outbursts in intermediate polars

Dwarf nova outbursts in intermediate polars

The role of flow geometry in influencing the stability criteria for low angular momentum axisymmetric black hole accretion

Spiral Waves in Accretion Discs— Observations

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