Publications of the MPIfR
Optical & Infrared
Interferometry Group
Keiichi Ohnaka, Thomas Driebe,
Karl-Heinz Hofmann, Thomas Preibisch, Dieter Schertl, and Gerd Weigelt
VLTI/MIDI observation of the silicate carbon
star Hen 38 (IRAS08002-3803): silicate dust reservoir spatially
resolved for the first time
Advances in Stellar Interferometry
Proceedings of SPIE: Vol. 6268, p.62682V-(1-5)
Danchi, W., Monnier, J., Schöller, M. (eds.)
Abstract
We present the results of N-band spectro-interferometric observations
of the silicate carbon star Hen 38 (IRAS08002-3803) with the
MID-infrared Interferometric instrument (MIDI) at the Very Large
Telescope Interferometer (VLTI) of the European Southern Observatory
(ESO). Our observations of IRAS08002-3803 with baseline lengths of
39-47 m 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. 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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