Cathie J. Clarke

Competitive accretion in embedded stellar clusters

We investigate the physics of gas accretion in young stellar clusters. Accretion in clusters is a dynamic phenomenon as both the stars and the gas respond to the same gravitational potential. Accretion rates are highly non-uniform with stars nearer the centre of the cluster, where gas densities are higher, accreting more than others. This competitive accretion naturally results in both initial mass segregation and a spectrum of stellar masses. Accretion in gas-dominated clusters is well modelled using a tidal-lobe radius instead of the commonly used Bondi–Hoyle accretion radius. This works as both the stellar and gas velocities are under the influence of the same gravitational potential and are thus comparable. The low relative velocity which results means that Rtidal<RBH in these systems. In contrast, when the stars dominate the potential and are virialized, RBH<Rtidal and Bondi–Hoyle accretion is a better fit to the accretion rates.

Photoevaporation of protoplanetary discs I: hydrodynamic models

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

Accretion in stellar clusters and the initial mass function

R_{in}^{1/2}

The effect of an external disk on the orbital elements of a central binary

(where

Characterizing the gravitational instability in cooling accretion discs

R_{in}

Observational implications of precessing protostellar discs and jets

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).

Statistical Confirmation of a Stellar Upper Mass Limit

We present a simple physical mechanism that can account for the observed stellar mass spectrum for masses

On the properties of young multiple stars

\ms \simgreat 0.5 \solm

The Jeans mass and the origin of the knee in the IMF

. The model depends solely on the competitive accretion that occurs in stellar clusters where each stars accretion rate depends on the local gas density and the square of the accretion radius. In a stellar cluster, there are two different regimes depending on whether the gas or the stars dominate the gravitational potential. When the cluster is dominated by cold gas, the accretion radius is given by a tidal-lobe radius. This occurs as the cluster collapses towards a

Dispersion in the lifetime and accretion rate of T Tauri discs

\rho\propto R^{-2}