Issue |
A&A
Volume 412, Number 1, December II 2003
|
|
---|---|---|
Page(s) | 133 - 145 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20031409 | |
Published online | 25 November 2003 |
Sulphur chemistry in the envelopes of massive young stars
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2
Sterrewacht, Postbus 9513, 2300 RA Leiden, The Netherlands
Corresponding author: F. F. S. van der Tak, vdtak@mpifr-bonn.mpg.de
Received:
9
December
2002
Accepted:
20
August
2003
The sulphur chemistry in nine regions in the earliest
stages of high-mass star formation is studied through single-dish
submillimeter spectroscopy. The line profiles indicate that
10–50% of the SO and SO2 emission arises in high-velocity gas,
either infalling or outflowing. For the low-velocity gas, excitation
temperatures are 25 K for H2S, 50 K for SO, H2CS, NS and HCS+,
and 100 K for OCS and SO2, indicating that most observed emission
traces the outer parts ( K) of the molecular envelopes,
except high-excitation OCS and SO2 lines. Abundances in the outer
envelopes, calculated with a Monte Carlo program, using the physical
structures of the sources derived from previous submillimeter
continuum and CS line data, are ~10-8 for OCS,
~10-9 for H2S, H2CS, SO and SO2, and ~10-10
for HCS+ and NS. In the inner envelopes (
K) of six
sources, the SO2 abundance is enhanced by a factor of
~100–1000. This region of hot, abundant SO2 has been seen
before in infrared absorption, and must be small,
0
2
(180 AU radius). The derived abundance profiles are consistent with
models of envelope chemistry which invoke ice evaporation at
K. Shock chemistry is unlikely to contribute. A major sulphur
carrier in the ices is probably OCS, not H2S as most models
assume. The source-to-source abundance variations of most molecules
by factors of ~10 do not correlate with previous systematic
tracers of envelope heating. Without observations of H2S and SO
lines probing warm (
100 K) gas, sulphur-bearing molecules
cannot be used as evolutionary tracers during star formation.
Key words: ISM: molecules / molecular processes / stars: circumstellar matter / stars: formation
© ESO, 2003
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