Issue |
A&A
Volume 445, Number 3, January III 2006
|
|
---|---|---|
Page(s) | 1015 - 1029 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053474 | |
Published online | 03 January 2006 |
High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument
Dusty environment spatially resolved
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: kohnaka@mpifr-bonn.mpg.de
2
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
3
European Southern Observatory, Casilla 19001, Santiago 19, Chile
4
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
5
Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
Received:
19
May
2005
Accepted:
12
September
2005
We present the results of N-band spectro-interferometric
observations of the silicate carbon star IRAS08002-3803 with the
MID-infrared Interferometric instrument (MIDI) at the
Very Large Telescope Interferometer (VLTI) of the European
Southern Observatory (ESO).
The observations were carried out using two unit telescopes
(UT2 and UT3) with projected baseline lengths ranging from 39 to 47 m.
Our observations of IRAS08002-3803
have spatially resolved the dusty environment of a
silicate carbon star for the first time and revealed an
unexpected wavelength dependence of the angular size in the N band:
the uniform-disk diameter is found to be constant and ~36 mas
(72 ) between 8 and 10 μm, while it steeply increases
longward of 10 μm to reach ~53 mas (106
)
at 13 μm.
Model calculations with our Monte Carlo radiative transfer code show
that neither spherical shell models nor axisymmetric disk
models consisting of silicate grains alone can simultaneously
explain the observed wavelength dependence of the visibility and
the spectral energy distribution (SED).
We propose that the circumstellar environment of IRAS08002-3803
may consist of two grain species coexisting in the disk:
silicate and a second grain species,
for which we consider amorphous carbon, large silicate grains, and
metallic iron grains.
Comparison of the observed visibilities and SED with our models
shows that such disk models can fairly – though not entirely
satisfactorily – reproduce the observed SED and
N-band visibilities.
Our MIDI observations and the
radiative transfer calculations lend support to the picture where
oxygen-rich material around IRAS08002-3803 is stored in a circumbinary
disk surrounding the carbon-rich primary star and its
putative low-luminosity companion.
Key words: infrared: stars / techniques: interferometric / stars: circumstellar matter / stars: carbon / stars: AGB and post-AGB / stars: individual: IRAS08002-3803
© ESO, 2006
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