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Self-gravity, Resonances, and Orbital Diffusion in Stellar Disks

Abstract : Fluctuations in a stellar system's gravitational field cause the orbits of stars to evolve. The resulting evolution of the system can be computed with the orbit-averaged Fokker-Planck equation once the diffusion tensor is known. We present the formalism that enables one to compute the diffusion tensor from a given source of noise in the gravitational field when the system's dynamical response to that noise is included. In the case of a cool stellar disk we are able to reduce the computation of the diffusion tensor to a one-dimensional integral. We implement this formula for a tapered Mestel disk that is exposed to shot noise and find that we are able to explain analytically the principal features of a numerical simulation of such a disk. In particular the formation of narrow ridges of enhanced density in action space is recovered. As the disk's value of Toomre's Q is reduced and the disk becomes more responsive, there is a transition from a regime of heating in the inner regions of the disk through the inner Lindblad resonance to one of radial migration of near-circular orbits via the corotation resonance in the intermediate regions of the disk. The formalism developed here provides the ideal framework in which to study the long-term evolution of all kinds of stellar disks.
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Submitted on : Tuesday, April 19, 2022 - 2:46:20 PM
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Jean-Baptiste Fouvry, James Binney, Christophe Pichon. Self-gravity, Resonances, and Orbital Diffusion in Stellar Disks. The Astrophysical Journal, 2015, 806, ⟨10.1088/0004-637X/806/1/117⟩. ⟨insu-03644938⟩

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