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Issue A&A
Volume 399, Number 1, February III 2003
Page(s) 169 - 175
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021798



A&A 399, 169-175 (2003)
DOI: 10.1051/0004-6361:20021798

Stringent upper limits to the solid NH $\mathsf{_3}$ abundance towards W 33A from near-IR spectroscopy with the Very Large Telescope

I. M. Taban1, W. A. Schutte1, K. M. Pontoppidan2 and E. F. van Dishoeck1, 2

1  Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
2  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands

(Received 19 September 2002 / Accepted 14 November 2002 )

Abstract
We obtained near-infrared spectroscopy of the high mass young stellar object W 33A between 1.9-2.5  $\mu$m in search of absorption features of circumstellar ices. The 2.27  $\mu$m band of $\rm CH_3OH$ is positively identified in the spectrum, its intensity being fully consistent with the column density derived earlier from the methanol bands at 3.54 and 3.91  $\mu$m. The 2.21  $\mu$m band of solid $\rm NH_3$, on the other hand, was not detected. This shows that the quantity of solid $\rm NH_3$ towards W 33A is at least 3 times lower than earlier estimates based on the $\rm NH_3$ umbrella mode at 9  $\mu$m.


Key words: methods: laboratory -- stars: individual: W 33A -- ISM: abundances -- ISM: molecules -- infrared: ISM -- ISM: lines and bands

Offprint request: W. A. Schutte, schutte@strw.leidenuniv.nl

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