Issue |
A&A
Volume 438, Number 2, August I 2005
|
|
---|---|---|
Page(s) | 557 - 570 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20042219 | |
Published online | 08 July 2005 |
Detection of steam in the circumstellar disk around a massive Young Stellar Object
1
Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: thi@science.uva.nl
2
ESA Research and Scientific Support Department, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
3
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
Received:
20
October
2004
Accepted:
18
March
2005
We report on the observation of hot water vapor (steam) in
the inner AU of a young massive star located in the star-forming
region IRAS 08576-4334. The water lines are detected in a
medium resolution () K-band spectrum taken by the
infrared spectrometer ISAAC mounted on the VLT-ANTU.
The water vapor is at a mean temperature of
K, cooler
than the hot CO found in the same object, which is at
1660 K; and the column density is N(H2O
cm-2. The profile of both H2O and CO lines is best reproduced by the emission from a Keplerian disk. To
interpret the data, we also investigate the formation of molecules
and especially CO and water vapor in the inner hot and dense part of
disks around young high mass stars using a pseudo time-dependent
gas-phase chemical model. Molecules are rapidly photodissociated
but this destruction is compensated for by an efficient formation
due to fast neutral-neutral reactions. The ability of CO molecules
to self-shield significantly enhances its abundance. Water molecules
are sufficiently abundant to be detectable. The observed H2O/CO ratio is reproduced by gas at 1600 K and by an enhanced UV field
over gas density ratio
. The
simulations support the presence of CO and H2O molecules in the
inner disks around young massive stars despite the strong UV radiation and show that the OH radical plays an essential role in
hot gas chemistry.
Key words: stars: formation / astrochemistry / circumstellar matter
© ESO, 2005
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