EDP Sciences
Free Access
Issue
A&A
Volume 412, Number 1, December II 2003
Page(s) 133 - 145
Section Formation, structure and evolution of stars
DOI https://doi.org/10.1051/0004-6361:20031409
Published online 25 November 2003


A&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 Dishoeck2

1  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, $\la$0 $\farcs$2 (180 AU radius). The derived abundance profiles are consistent with models of envelope chemistry which invoke ice evaporation at $T\sim
100$  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 ( $\ga$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

SIMBAD Objects



© ESO 2003

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.