We present the first diffraction–limited speckle masking observations of the oxygen–rich AGB star AFGL 2290 .
The speckle interferograms were recorded with the Russian 6 m SAO telescope .
At the wavelength 2.11 { \mu m } a resolution of 75 milli–arcsec ( mas ) was obtained .
The reconstructed diffraction–limited image reveals that the circumstellar dust shell ( CDS ) of AFGL 2290 is at least slightly non–spherical .
The visibility function shows that the stellar contribution to the total 2.11 { \mu m } flux is less than \sim 40 \% , indicating a rather large optical depth of the circumstellar dust shell .
The 2–dimensional Gaussian visibility fit yields a diameter of AFGL 2290 at 2.11 { \mu m } of 43 mas \times 51 mas , which corresponds to a diameter of 42 AU \times 50 AU for an adopted distance of 0.98 kpc .

Our new observational results provide additional constraints on the CDS of AFGL 2290 , which supplement the information from the spectral energy distribution ( SED ) .
To determine the structure and the properties of the CDS we have performed radiative transfer calculations for spherically symmetric dust shell models .
The observed SED approximately at phase 0.2 can be well reproduced at all wavelengths by a model with T _ { eff } = 2000 { K } , a dust temperature of 800 K at the inner boundary r _ { 1 } , an optical depth \tau _ { V } = 100 and a radius for the single–sized grains of a _ { gr } = 0.1 { \mu m } .
However , the 2.11 { \mu m } visibility of the model does not match the observation .

Exploring the parameter space , we found that 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 0.16 { \mu m } and a higher \tau _ { V } = 150 , the observed visibility can be reproduced preserving the match of the SED at longer wavelengths .
Nevertheless , the model shows a deficiency of flux at short wavelengths , which is attributed to the model assumption of a spherically symmetric dust distribution , whereas the actual structure of the CDS around AFGL 2290 is in fact non–spherical .
Our study demonstrates the possible limitations of dust shell models which are constrained solely by the spectral energy distribution , and emphasizes the importance of high spatial resolution observations for the determination of the structure and the properties of circumstellar dust shells around evolved stars .