Session 49 - Young Stellar Objects.
Display session, Tuesday, January 14
Metropolitan Ballroom,

## [49.12] Externally Induced Evaporation of Young Stellar Disks: The Case for HST 10 in Orion's Trapezium.

D. Johnstone (CITA, U. Toronto), D. Hollenbach, H. Storzer (NASA/Ames), J. Bally (APAS, U. Colorado), R. Sutherland (Theory Centre, ANU)

The Trapezium region in Orion is composed of a few high-mass stars, responsible for the ionization of the surrounding gas, and a plethora of low-mass stars with disks. Observations at infrared, optical, and radio wavelengths have led to the discovery of extended ionized envelopes around many of the young low-mass stars requiring evaporation rates \dot M \sim 10^-7 M_\hboxødot/yr. In this poster we explain these observations through a model for the evaporation of disks around young low-mass stars by an external source of high energy photons. In particular, the externally produced ultraviolet continuum longward of the Lyman limit is used to heat the disk surface and produce a warm neutral flow. The model results in an offset ionization front, where the neutral flow encounters Lyman continuum radiation, and a mass-loss rate which is fixed due to the self-regulating nature of FUV heating. Applying this model to the Trapezium region evaporating objects, particularly HST 10, produces a satisfactory solution to both the mass-loss rate and the size of the ionized envelopes. The resulting short destruction times for these disks constrain the gestation period for planet embryos around stars in dense clusters.