Astrophysics, abstract
astro-ph/0603253

From: Richard Alexander [view email]

Date: Thu, 9 Mar 2006 23:18:59 GMT (301kb)

Photoevaporation of protoplanetary discs I: hydrodynamic models

Authors: R.D.Alexander, C.J.Clarke, J.E.Pringle

Comments: 13 pages, 9 figures. Accepted for publication in MNRAS

In this paper we consider the effect of the direct ionizing stellar radiation field on the evolution of protoplanetary discs subject to photoevaporative winds. We suggest that models which combine viscous evolution with photoevaporation of the disc (e.g. Clarke, Gendrin & Sotomayor 2001) incorrectly neglect the direct field after the inner disc has drained, at late times in the evolution. We construct models of the photoevaporative wind produced by the direct field, first using simple analytic arguments and later using detailed numerical hydrodynamics. We find that the wind produced by the direct field at late times is much larger than has previously been assumed, and we show that the mass-loss rate scales as $R_{in}^{1/2}$ (where $R_{in}$ is the radius of the instantaneous inner disc edge). We suggest that this result has important consequences for theories of disc evolution, and go on to consider the effects of this result on disc evolution in detail in a companion paper (Alexander, Clarke & Pringle 2006b).

http://arxiv.org/abs/astro-ph/0603253

Astrophysics, abstract
astro-ph/0603254

From: Richard Alexander [view email]

Date: Thu, 9 Mar 2006 23:29:08 GMT (86kb)

Photoevaporation of protoplanetary discs II: evolutionary models and observable properties

Authors: R.D.Alexander, C.J.Clarke, J.E.Pringle

Comments: 11 pages, 5 figures. Accepted for publication in MNRAS

We present a new model for protoplanetary disc evolution. This model combines viscous evolution with photoevaporation of the disc, in a manner similar to Clarke, Gendrin & Sotomayor (2001). However in a companion paper (Alexander, Clarke & Pringle 2006a) we have shown that at late times such models must consider the effect of stellar radiation directly incident on the inner disc edge, and here we model the observational implications of this process. We find that the entire disc is dispersed on a time-scale of order $10^5$yr after a disc lifetime of a few Myr, consistent with observations of T Tauri (TT) stars. We use a simple prescription to model the spectral energy distribution of the evolving disc, and demonstrate that the model is consistent with observational data across a wide range of wavelengths. We note also that the model predicts a short ``inner hole'' phase in the evolution of all TT discs, and make predictions for future observations at mid-infrared and millimetre wavelengths.

http://arxiv.org/abs/astro-ph/0603254