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TwitterA&A 412, 133-145 (2003)
DOI: 10.1051/0004-6361:20031409
Sulphur chemistry in the envelopes of massive young stars
F. F. S. van der Tak1, A. M. S. Boonman2, R. Braakman2 and E. F. van Dishoeck21 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Sterrewacht, Postbus 9513, 2300 RA Leiden, The Netherlands
(Received 9 December 2002 / Accepted 20 August 2003)
Abstract
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 SO
2 emission arises in high-velocity gas,
either infalling or outflowing. For the low-velocity gas, excitation
temperatures are 25 K for H
2S, 50 K for SO, H
2CS, NS and HCS
+,
and 100 K for OCS and SO
2, indicating that most observed emission
traces the outer parts (
T<100 K) of the molecular envelopes,
except high-excitation OCS and SO
2 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 H
2S, H
2CS, SO and SO
2, and ~10
-10
for HCS
+ and NS. In the inner envelopes (
T>100 K) of six
sources, the SO
2 abundance is enhanced by a factor of
~100-1000. This region of hot, abundant SO
2 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 H
2S 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 H
2S 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
Offprint request: F. F. S. van der Tak, vdtak@mpifr-bonn.mpg.de
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