The gravitational radius of an irradiated disk

Abstract

We derive an updated, analytic formula for the gravitational radius, rg, of an irradiated, thin disk. For such a disk, the region outside the gravitational radius will produce a thermal wind, while the region interior to the gravitational radius will be stable. We find that rg ≈ 1.4 (M*/Mo)/(T0/104 K) AU. The value of 1.4 AU is approximately one fifth of currently used values. The analysis uses the adiabatic approximation. We argue that the same formula applies for the non-adiabatic, isothermal case. © Astronomical Society of Australia 2003.