Vendredi 4 Octobre 2002, à 14h, Paris, 77 avenue Denfert Rochereau, 14h
77 avenue Denfert Rochereau, Paris 14
Salle de l'Atelier, Observatoire de Paris
DISK DISPERSAL AROUND YOUNG STARS
David HOLLENBACH
NASA Ames Research Center
Résumé :
We first review the evidence pertaining to
the lifetimes of planet-forming disks of gas and dust around young stars
and discuss possible disk dispersal mechanisms:
1) viscous accretion of material onto the central source, 2) close
stellar encounters, 3) stellar winds,
and 4) photoevaporation caused by the heating of the disk surface
by ultraviolet radiation. Photoevaporation
is likely the most important dispersal mechanism for the outer
regions of disks, and this talk focuses on the evaporation
caused by the presence of a nearby, luminous star rather than the
central star itself. We also focus on disks around low-mass stars
like the Sun rather than high-mass stars, which we have treated
previously. Stars often form in clusters and the ultraviolet flux
from the most luminous star in the cluster can have a dramatic
effect on the disk orbiting a nearby low-mass star.
We apply our theoretical models to the evaporating protoplanetary disks
(or "proplyds") in the Trapezium cluster in Orion, to the formation
of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and
to the formation of Kuiper belts around low mass stars. We find a
possible explanation for the differences between Neptune and Jupiter,
and make a prediction concerning recent searches for giant planets
in large clusters.
