  We present the first diffraction-limited speckle masking observations of the
oxygen-rich AGB star AFGL 2290. The data was obtained with the Russian 6m SAO
telescope. At the wavelength of 2.11um a resolution of 75mas was achieved. The
reconstructed image reveals that the CDS of AFGL 2290 is slightly
non-spherical. The stellar contribution to the total 2.11um flux is less than
\~40%. The 2D Gaussian visibility fit yields a diameter of AFGL 2290 at 2.11um
of 43mas x 51mas, corresponding to 42AU x 50AU for an adopted distance of
0.98kpc. Our results provide additional constraints on the CDS of AFGL 2290,
which supplement the information from the SED. We have performed radiative
transfer calculations for spherically symmetric dust shell models. The observed
SED at phase ~0.2 can be well reproduced at all wavelengths by a model with
Teff=2000K, a dust temperature of 800K at the inner boundary, an optical depth
tau_V=100 and a radius for the single-sized grains of 0.1um. However, the
2.11um visibility of the model does not match the observation. We found that
the grain size is the key parameter in achieving a fit of the observed
visibility while retaining the match of the SED, at least partially. Both the
slope and the curvature of the visibility strongly constrain the possible grain
radii. On the other hand, the SED at longer wavelengths, the silicate feature
in particular, determines the dust mass loss rate and, thereby, restricts the
possible optical depths of the model. With a larger grain size of 0.16um and a
higher tau_V=150, the observed visibility can be reproduced preserving the
match of the SED at longer wavelengths.
