SCYON Abstract
Received on February 1 2001
Destruction of Protoplanetary Disks in the Orion Nebula Cluster
Abstract
We use numerical N-body simulations of the Orion Nebula Cluster (ONC)
to investigate the destruction of protoplanetary disks by close stellar
encounters and UV radiation from massive stars. The simulations model
a cluster of 4000 stars, and we consider separately cases in which the
disks have fixed radii of 100 AU and 10 AU. In the former case,
depending on a star's position and orbit in the cluster over 107
years, UV photoevaporation removes at least 0.01 MO from its disk,
and can remove up to 1 MO. We find no dynamical models of the ONC
consistent with the suggestion of Störzer and Hollenbach (1999, ApJ 515, 669)
that the observed distribution and abundance of
proplyds could be explained by a population of stars on radial orbits
which spend relatively little time near theta1C Ori (the most massive star
in the ONC). Instead the observations require either massive disks
(e.g. a typical initial disk mass of 0.4 MO) or a very recent birth
for theta1 C Ori. When we consider the photoevaporation of the inner 10 AU of
disks in the ONC, we find that planet formation would be hardly
affected. Outside that region, planets would be prevented from forming
in about half the systems, unless either the initial disk masses were
very high (e.g. 0.4 MO) or they formed quickly (in less than ~
2 Myr) and theta1 C Ori has only very recently appeared.
We also present statistics on the distribution of minimum stellar
encounter separations. This peaks at 1000 AU, with only about
4 per cent of stars having had an encounter closer than 100 AU at the
cluster's present age, and less than 10 per cent after 107 years.
We conclude that stellar encounters are unlikely to play a significant
role in destroying protoplanetary disks. In the absence of any
disruption mechanism other than those considered here, we would thus
predict planetary systems like our own to be common amongst stars
forming in ONC-like environments.
Also, although almost all stars will have experienced an encounter at
the radius of the Oort cloud in our own system, this only places a firm
constraint on the possible birthplace of the Sun if the Oort cloud
formed in situ, rather than through the secular ejection of matter from
the planetary zone.