Irradiation Instability at the Inner Edges of Accretion Disks

Jeffrey Fung, Pawel Artymowicz
Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, Canada M5S 3H4
arXiv:1403.4244 [astro-ph.EP], (17 Mar 2014)


   author={Fung}, J. and {Artymowicz}, P.},

   title={"{Irradiation Instability at the Inner Edges of Accretion Disks}"},

   journal={ArXiv e-prints},




   keywords={Astrophysics – Earth and Planetary Astrophysics},




   adsnote={Provided by the SAO/NASA Astrophysics Data System}


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An instability can potentially operate in highly irradiated disks where the disk sharply transitions from being radially transparent to opaque (the ‘transition region’). Such conditions may exist at the inner edges of transitional disks around T Tauri stars and accretion disks around AGNs. We derive the criterion for this instability, which we term the ‘irradiation instability’, or IRI. We also present the linear growth rate as a function of beta, the ratio between radiation force and gravity, and c_s, the sound speed of the disk, obtained using two methods: a semi-analytic analysis of the linearized equations and a numerical simulation using the GPU-accelerated hydrodynamical code PEnGUIn. In particular, we find that IRI occurs at beta~0.1 if the transition region extends as wide as ~0.05r, and at higher beta values if it is wider. Furthermore, in the nonlinear evolution of the instability, disks with a large beta and small c_s exhibit ‘clumping’: extreme local surface density enhancements, reaching a few tens of the initial disk surface density.
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