Issue |
A&A
Volume 447, Number 3, March I 2006
|
|
---|---|---|
Page(s) | 963 - 969 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053639 | |
Published online | 10 February 2006 |
Infrared detection of gas phase formaldehyde towards the high mass protostar W33A
1
Laboratoire Univers et Théorie, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, Place Jules Janssen, 92195 Meudon, France e-mail: evelyne.roueff@obspm.fr
2
IAS, Bat. 121, Université Paris Sud, 91405 Orsay Cedex, France
3
Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720, USA
4
Laboratoire d'Étude du Rayonnement et de la Matière en Astrophysique, UMR 8112 du CNRS, Observatoire de Paris and École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France
Received:
16
June
2005
Accepted:
17
October
2005
We report the detection of numerous absorption lines of the band
of gaseous formaldehyde (H2CO) near 3.6 μm towards the high-mass
protostar W33A. This is the first infrared detection of gaseous H2CO in
an interstellar cloud. An upper limit toward RAFGL 7009S is also reported.
The column density of H2CO detected at 3.6 μm toward W33A is much
higher than that measured in large beam millimeter wave observations
toward the same source, suggesting that it is concentrated close to the
infrared continuum source. The mean temperature of the H2CO, derived
from LTE spectral modelling, is ~100 K, which is close to the values
found for most other gas phase species observed in absorption and is the
expected temperature of the cloud at the dust mantle sublimation
interface, implying a large jump in the abundance of gaseous H2CO from
the surrounding cold cloud to the warm gas. The ratio of gaseous and solid
H2CO column densities is about 0.03 for W33A and less than 0.02 for
RAFGL 7009S. We discuss this detection in the context of the two most
likely mechanisms for H2CO formation: grain mantle evaporation, and gas
phase reactions between species produced by photodissociation of grain
mantle evaporants.
Key words: ISM: molecules / molecular processes / stars: circumstellar matter / stars: formation
© ESO, 2006
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