Global Disk Oscillation Modes in Cataclysmic Variables and Other Newtonian Accretors

Ortega‐Rodríguez, Manuel; Wagoner, Robert V.

doi:10.1086/521419

Cited by 4 publications

(1 citation statement)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this weak-field case, κ = Ω = Ω ⊥ , so there is no turnover in the radial epicyclic frequency. There is an inner boundary (at radius r i ), which we have taken to be impenetrable in this initial investigation [11]. As shown in Figure 10, g-modes are trapped as usual where ω 2 < κ 2 = Ω 2 , which gives the eigenfrequency |σ m | < (m + 1)Ω.…”

Section: Newtonian G-modesmentioning

confidence: 97%

Diskoseismology

Wagoner¹

2008

J. Phys.: Conf. Ser.

View full text Add to dashboard Cite

Abstract. The normal mode oscillations of (geometrically thin) accretion disks around black holes and other compact objects will be analyzed and contrasted with those in stars. For black holes, the most robust modes are gravitationally trapped near the radius at which the radial epicyclic frequency is maximum. Their eigenfrequencies depend mainly on the mass and angular momentum of the black hole. The fundamental g-mode has recently been seen in numerical simulations of black hole accretion disks. For stars such as white dwarfs, the modes are trapped near the inner boundary (magnetospheric or stellar) of the accretion disk. Their eigenfrequencies are approximately multiples of the (Keplerian) angular velocity of the inner edge of the disk. The relevance of these modes to the high frequency quasi-periodic oscillations observed in the power spectra of accreting binaries will be discussed. In contrast to most stellar oscillations, most of these modes are unstable in the presence of viscosity (if the turbulent viscosity induced by the magnetorotational instability acts hydrodynamically). Introduction; comparison with helio-and asteroseismologyWe shall briefly review the application of normal mode analysis, so successfully employed in stars (as this conference illustrates), to the ubiquitous accretion disks that surround a wide variety of objects (black holes, neutron stars, white dwarfs, and protostars). In the first three cases (except for the supermassive black holes observed at the center of galaxies), they are usually maintained by gas tidally drawn through the inner Lagrange point from their companion star in a binary. The relativistic formulation of diskoseismology was initiated by S. Kato and J. Fukue in 1980 [1], and reviews can be found in [2,3,4].Let us briefly compare the adiabatic hydrodynamic perturbations of stars and accretion disks in the Newtonian limit. We shall assume that the gravitational field of the disk (including that of the perturbations) is negligible, which is an excellent approximation for most accretion disks since their mass is much less than that of the central object. To facilitate the comparison, we shall also make the same (Cowling) approximation for the perturbations of the star. We shall consider the usual case of geometrically thin (and optically thick) accretion disks: thickness h(r) ∼ c s /Ω much less than the radial distance r, where c s (then much less than v φ = rΩ) is the sound speed and Ω(r) is the angular velocity of the disk. The pressure gradient is then much greater vertically than radially; and the motion of the unperturbed gas is close to that of free-particle orbits, with v z v r v φ . The unperturbed disk is axially symmetric, with z the distance from its midplane (about which it is reflection symmetric). Throughout, we also make a WKB approximation (usually valid) that the perturbation radial wavelength λ r r. The governing equations of motion of perturbations of a (slowly rotating) star (left) and an

show abstract

Section: Newtonian G-modesmentioning

confidence: 97%