m and 6.8m absorption
bands
in luminous young stellar objects.
Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands
ISO SWS spectra (2 - 45 m) have been obtained towards a large number
of luminous young stellar objects. These new high resolution observations
have given us the unique opportunity to conduct the first in depth study
of the 6.0m and 6.8m absorption features. We will present a
study of profile changes between the sources. By fitting
various black body continua to all the sources it was noted that the shape and
intrinsic properties of the 6.0m and 6.8m absorption features
remained unchanged. This indicates that the shape of the 6.0m and
6.8m are robust.
Previous work has already identified that the 6.0m is caused by
amorphous water ice. From these new observations it is clear that at least
two other components contribute to this ice feature at the short
(5.8m) and long (6.2m) wavelength wings.
By fitting the 6.0m
with laboratory water ice profiles of varying temperature (10K - 120K) we
present a pictorial display of how influential these two components are on
the 6.0m. The extent of the blue and red excess varies significantly
from source to source. We suggest likely components that contribute to
the blue (HCOOH) and red (PAH in absorption) excess. The FWHM and the
peak position of the 6.0m vary from source to source.
A similar study has been conducted for the 6.8m absorption
feature. Large peak position changes, up to 0.15m, are seen between
the sources. Also, the profile of the 6.8m varies dramatically from
source to source. By fitting source
profiles to each other and determining the residuals, it seems likely
that the 6.8m band is caused by at least 2
components. Furthermore, variations in the correlation of the
6.0m and 6.8m are seen.