Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
A. Gauger, P. Irrgang, R. Osterbart, G.
Schniggenberg, G. Weigelt
and Y. Balega:
Speckle Masking Imaging and Radiative
Transfer Modeling of
the Oxygen-Rich Dust Shells of AFGL 2290 and CIT 3
Astronomische Gesellschaft Meeting Abstracts
(AGM 14, P33)
Poster presented at the Annual Scientific Meeting of the Astronomische
Gesellschaft
at Heidelberg, September 14-19, 1998
Abstract.
High spatial resolution observations directly provide information
on important properties of circumstellar
dust shells (CDS) around asymptotic giant branch (AGB) stars,
such as the dimensions and the geometry of
the shell, and therefore contribute strong constraints for the
radiative transfer modeling of these circumstellar environments.
We present the first diffraction-limited speckle masking observations
of the
oxygen-rich AGB stars AFGL 2290 (OH 39.7+1.5) and CIT 3 (IRC+10011)
at near infrared wavelengths. The speckle interferograms were
obtained with the Russian SAO 6m telescope.
We achieved the diffraction-limited resolutions of 56 mas at
1.65 micron and 76 mas at 2.2 micron.
The CDS of AFGL 2290 is found to be slightly asymmetric with a mean
Gaussian FWHM diameter of 42 mas at a wavelength of 2.2 micron.
The derived visibility yields an upper limit for the stellar flux
contribution at 2.2 micron of 40%,
suggesting a rather high optical depth.
We have found that radiative transfer models assuming a spherically
symmetric dust shell either reproduce the observed spectral energy
distribution, or the measured visibility of AFGL 2290,
but not both simultaneously. This behaviour is interpreted as being due
to
a non-spherical dust distribution.
The observations of CIT 3 showed that its CDS has a two component
structure: a compact inner component with a Gaussian FWHM diameter of
40 mas at a wavelength of 2.2 micron,
and a weaker nebulosity, which is several times more extended.
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