HST and VLT observations of PROPLYDS in the giant HII region NGC 3603
Wolfgang Brandner,
Eva K. Grebel, You-Hua Chu,
Horacio Dottori, Bernhard Brandl, Sabine Richling, Harold W. Yorke,
Sean D. Points, and Hans Zinnecker
2000 AJ 119, 292
Abstract
We report the discovery of three proplyd-like structures in the giant HII
region NGC 3603. The emission nebulae are clearly resolved in narrow-band
and broad-band HST/WFPC2 observations in the optical and broad-band
VLT/ISAAC observations in the near-infrared. All three nebulae are tadpole
shaped, with the bright ionization front at the head facing the central
cluster and a fainter ionization front around the tail pointing away
from the cluster. Typical sizes are 6,000 A.U. times
20,000 A.U. The nebulae share the overall morphology of the proplyds
(`PROto PLanetarY DiskS') in Orion, but are 20 to 30 times larger in size.
Additional faint filaments located between the nebulae and the
central ionizing cluster can be interpreted as bow shocks resulting
from the interaction of the fast winds from the high-mass stars in the cluster
with the evaporation flow from the proplyds.
Low-resolution spectra of the brightest nebula,
which is at a projected separation of 1.3 pc from the cluster, reveal
that it has the spectral excitation characteristics of an Ultra Compact
HII region with electron densities well in excess of 10E4/cm^3.
The near-infrared data reveal a point-source superimposed on the
ionization front.
The striking similarity of the tadpole shaped emission nebulae in NGC 3603
to the proplyds in Orion suggests that the physical structure of both types
of objects might be the same. We present 2D radiation hydrodynamical
simulations of an externally illuminated star-disk-envelope system,
which was still in its main accretion phase when first
exposed to ionizing radiation from the central cluster.
The simulations reproduce the overall morphology of the proplyds
in NGC 3603 very well, but also indicate that
mass-loss rates of up to 10E-5 Mo/yr are required in
order to explain the size of the proplyds.
Due to these high mass-loss rates, the proplyds in NGC 3603 should only
survive approx 10E5 yr. Despite this short survival time,
we detect three proplyds. This indicates that circumstellar disks
must be common around young stars in NGC 3603 and that these particular
proplyds have only recently been exposed to their present harsh UV
environment.
A copy of the article is available at
AJ and the
LANL Preprint Server.
More information on NGC 3603 is available here.