Issue |
A&A
Volume 399, Number 3, March I 2003
|
|
---|---|---|
Page(s) | 1037 - 1046 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20021921 | |
Published online | 14 February 2003 |
The mineralogy, geometry and mass-loss history of IRAS 16342–3814*
1
Astronomical Institute, “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2
Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
3
Dept. of Physics, UMIST, Sackville Street, PO Box 88, Manchester M60 1QD, UK
Corresponding author: C. Dijkstra, dijkstra@astro.uva.nl
Received:
7
October
2002
Accepted:
18
November
2002
We present the m Infrared Space
Observatory (ISO) spectrum and
m ISAAC and TIMMI2
images of the extreme OH/IR star IRAS 16342–3814. Amorphous silicate
absorption features are seen at 10 and
m, together with
crystalline silicate absorption features up to almost
m. No
other OH/IR star is known to have crystalline silicate features in
absorption up to these wavelengths. This suggests that IRAS 16342–3814 must
have, or recently had, an extremely high mass-loss rate. Indeed,
preliminary radiative transfer calculations suggest that the mass-loss rate
may be as large as
. The
m ISAAC image shows a bipolar reflection nebula with a
dark equatorial waist or torus, similar to that seen in optical images
taken with the Hubble Space Telescope (HST). The position angle of
the nebula decreases significantly with increasing wavelength, suggesting
that the dominant source of emission changes from scattering to thermal
emission. Still, even up to
m the nebula is oriented
approximately along the major axis of the nebula seen in the HST and ISAAC
images, suggesting that the torus must be very cold, in agreement with the
very red ISO spectrum. The
m image shows a roughly
spherically symmetric extended halo, approximately
in diameter, which
is probably due to a previous phase of mass-loss on the AGB, suggesting a
transition from a (more) spherically symmetric to a (more) axial symmetric
form of mass-loss at the end of the AGB. Using a simple model, we estimate
the maximum dust particle sizes in the torus and in the reflection nebula
to be 1.3 and
m respectively. The size of the particles in
the torus is large compared to typical ISM values, but in agreement with
high mass-loss rate objects like AFGL 4106 and HD161796. We discuss the
possible reason for the difference in particle size between the torus and
the reflection nebula.
Key words: circumstellar matter / infrared: stars / stars: AGB and post-AGB / stars: imaging / stars: mass-loss
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE. Also based on observations obtained at the European Southern Observatory (ESO).
© ESO, 2003
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