A&A Supplement Ser., Vol. 124, August 1997, 205-253
Received February 28; accepted September 30, 1996
F.P. Helmich
- E.F. van Dishoeck
Send offprint request: E.F. van Dishoeck
Leiden Observatory, P.O.-Box 9513, 2300 RA Leiden, The
Netherlands
-
SRON Laboratory Groningen, P.O.-Box 800, 9700 AV Groningen, The
Netherlands
Results are presented of the 345 GHz spectral survey toward three
sources in the W 3 Giant Molecular Cloud: W 3 IRS4, W 3 IRS5 and
W 3(
). Nearly 90% of the atmospheric window between 334 and
365 GHz has been scanned using the James Clerk Maxwell Telescope
(JCMT) down
to a noise level of 
per resolution element. These
observations are complemented by a large amount of data in the 230 GHz
atmospheric window. From this data set physical conditions and
beam-averaged column densities are derived for more than 14 chemically
different species (over 24 different isotopes). The physical parameters
derived in Paper I (Helmich et al. 1994) are confirmed by the analysis
of the excitation of other species, although there is evidence that the
silicon- and sulfur-bearing molecules exist in a somewhat denser and
warmer environment. The densities are high, 
, in
the three sources and the kinetic temperatures for the bulk of the gas
range from 55 K for IRS4 to 220 K for W 3(
). The chemical
differences between the three sources are very striking: silicon- and
sulfur-bearing molecules such as SiO and 
are prominent toward
IRS5, whereas organic molecules like 
, 
and
are at least an order of magnitude more abundant toward
W 3(
). Vibrationally excited molecules are also detected toward
this source. Only simple molecules are found toward IRS4. The data
provide constraints on the amount of deuterium fractionation and the
ionization fraction in the observed regions as well. These chemical
characteristics are discussed in the context of an evolutionary
sequence, in which IRS5 is the youngest, W 3(
) somewhat older and
IRS4, although still enigmatic, the oldest.
keywords: ISM: molecules -- ISM: clouds -- ISM: individual: W 3 IRS5,
W 3 IRS4, W 3(
) -- surveys -- radio lines: ISM