On the dynamics of a twisted disc immersed in a radiation field

Abstract

We study the dynamics of a twisted tilted disc under the influence of an external radiation field. Assuming the effect of absorption and reemission/scattering is that a pressure is applied to the disc surface where the local optical depth is of order unity, we determine the response of the vertical structure and the influence it has on the possibility of instability to warping. We derive a pair of equations describing the evolution of a small tilt as a function of radius in the small amplitude regime that applies to both the diffusive and bending wave regimes. We also study the non linear vertical response of the disc numerically using an analogous one dimensional slab model. For global warps, we find that in order for the disc vertical structure to respond as a quasi uniform shift or tilt, as has been assumed in previous work, the product of the ratio of the external radiation momentum flux to the local disc mid plane pressure, where it is absorbed, with the disc aspect ratio should be significantly less than unity. Namely, this quantity should be of the order of or smaller than the ratio of the disc gas density corresponding to the layer intercepting radiation to the mid plane density, $\lambda \ll 1$. When this condition is not satisfied the disc surface tends to adjust so that the local normal becomes perpendicular to the radiation propagation direction. In this case dynamical quantities determined by the disc twist and warp tend to oscillate with a large characteristic period $T_{\ast }\sim {\lambda }^{-1}{T}_K$, where $T_K$ is some 'typical' orbital period of a gas element in the disc. The possibility of warping instability then becomes significantly reduced. In addition, when the vertical response is non uniform, the possible production of shocks may lead to an important dissipation mechanism.

arXiv commentsubmitted to MNRAS

References in corpus (10)

• Precessing warped accretion discs in X-ray binaries
• Hydrodynamic Simulations of the Bardeen-Petterson Effect
• The Structure and X-ray Recombination Emission of a Centrally Illuminated Accretion Disk Atmosphere and Corona
• Long-term Properties of Accretion Disks in X-ray Binaries: II. Stability of Radiation-Driven Warping
• Hydrodynamic Simulations of Propagating Warps and Bending Waves In Accretion Discs
• Warping and Precession of Accretion Disks Around Magnetic Stars: Nonlinear Evolution
• Radiation-Driven Warping. II. Non-Isothermal Disks
• Three dimensional SPH simulations of radiation-driven warped accretion discs
• A Wind Driven Warping Instability in Accretion Disks
• On the dynamics of a twisted disc immersed in a radiation field

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