Publications of the MPIfR
Optical & Infrared
Interferometry Group
K. Ohnaka, T. Driebe, K.-H. Hofmann,
Ch. Leinert, S. Morel, S. Paresce, Th.Preibisch, A. Richichi, D.
Schertl, M. Schöller, L.B.F.M. Waters, G. Weigelt, M. Wittkowski
High angular resolution N-band observation of
the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument
Astronomy & Astrophysics, 445, pg.1015-1029
(Section 'Interstellar and circumstellar matter') (2006)
Abstract
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
R_) between 8 and 10 µm, while it steeply increases
longward of 10 µm to reach ~53 mas (106 R_) 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.
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