CIT 3 is an oxygen-rich long-period variable evolving along the Asymptotic Giant Branch and is one of the most extreme infrared AGB objects .
Due to substantial mass loss it is surrounded by an optically thick dust shell which absorbs almost all visible light radiated by the star and finally re-emits it in the infrared regime .
We present the first near infrared bispectrum speckle-interferometry observations of CIT 3 in the J - , H - , and K ^ { \prime } -band .
The J - , H - , and K ^ { \prime } -band resolution is 48 mas , 56 mas , and 73 mas , resp .
The interferograms were obtained with the Russian 6 m telescope at the Special Astrophysical Observatory .
While CIT 3 appears almost spherically symmetric in the H - and K ^ { \prime } -band it is clearly elongated in the J -band along a symmetry axis of position angle -28 \degr .
Two structures can be identified : a compact elliptical core and a fainter north-western fan-like structure .
The eccentricity of the elliptical core , given by the ratio of minor to major axis , is approximately \varepsilon =123 mas/154 mas=0.8 .
The full opening angle of the fan amounts to approximately 40 \degr .
Extensive radiative transfer calculations have been carried out and confronted with the observations taking into account the spectral energy distribution ranging from 1 \mu m to 1 mm , our near-infrared visibility functions at 1.24 \mu m , 1.65 \mu m and 2.12 \mu m , as well as 11 \mu m ISI interferometry .
The best model found to match the observations refers to a cool central star with T _ { eff } = 2250 K which is surrounded by an optically thick dust shell with \tau ( 0.55 \mu m ) = 30 .
The models give a central-star diameter of \Theta _ { \ast } = 10.9 mas and an inner dust shell diameter of \Theta _ { 1 } = 71.9 mas being in line with lunar occultation observations .
The inner rim of the dust-shell is located at r _ { 1 } = 6.6 R _ { \ast } and has a temperature of T _ { 1 } = 900 K. The grain sizes were found to comply with a grain-size distribution according to Mathis et al .
( 1977 ) with n ( a ) \sim a ^ { -3.5 } , and 0.005 \mu { m } \leq a \leq 0.25 \mu m. Uniform outflow models , i.e .
density distributions with \rho \sim 1 / r ^ { 2 } , turned out to underestimate the flux beyond 20 \mu m. A two-component model existing of an inner uniform-outflow shell region ( \rho \sim 1 / r ^ { 2 } ) and an outer region where the density declines more shallow as \rho \sim 1 / r ^ { 1.5 } proved to remove this flux deficiency and to give the best overall match of the observations .
The transition between both density distributions is at r _ { 2 } = 20.5 r _ { 1 } = 135.7 R _ { \ast } where the dust-shell temperature has dropped to T _ { 2 } = 163 K. Provided the outflow velocity kept constant , the more shallow density distribution in the outer shell indicates that mass-loss has decreased with time in the past of CIT 3 .
Adopting v _ { exp } = 20 km/s , the termination of that mass-loss decrease and the begin of the uniform-outflow phase took place 87 yr ago .
The present-day mass-loss rate can be determined to be \dot { M } = ( 1.3 - 2.1 ) \cdot 10 ^ { -5 } M _ { \odot } /yr for d = 500 - 800 pc .