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Issue A&A
Volume 376, Number 1, September II 2001
Page(s) L5 - L8
Section Letters
DOI 10.1051/0004-6361:20011008



A&A 376, L5-L8 (2001)
DOI: 10.1051/0004-6361:20011008

Gas-phase SO $_\mathsf{2}$ in absorption towards massive protostars

J. V. Keane1, A. M. S. Boonman2, A. G. G. M. Tielens1, 3 and E. F. van Dishoeck2

1  Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
3  SRON, PO Box 800, 9700 AV Groningen, The Netherlands

(Received 18 June 2001 / Accepted 11 July 2001)

Abstract
We present the first detection of the ${\nu_{\rm 3}}$ ro-vibrational band of gas-phase ${\rm SO_2}$ in absorption in the mid-infrared spectral region around 7.3 ${\rm\mu m}$ of a sample of deeply embedded massive protostars. Comparison with model spectra shows that the derived excitation temperatures correlate with previous C2H2 and HCN studies, indicating that the same warm gas component is probed. The ${\rm SO_2}$ column densities are similar along all lines of sight suggesting that the ${\rm SO_2}$ formation has saturated, but not destroyed, and the absolute abundances of ${\rm SO_2}$ are high (~10-7). Both the high temperature and the high abundance of the detected ${\rm SO_2}$ are not easily explained by standard hot core chemistry models. Likewise, indicators of shock induced chemistry are lacking.


Key words: star-formation: gas-phase molecules -- ISM: abundances -- ISM: molecules

Offprint request: J. V. Keane, jacquie@astro.rug.nl

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