  We present observations of the famous OH/IR star OH26.5+0.6 obtained using
the Mid-Infrared Interferometric Instrument MIDI at the European Southern
Observatory (ESO) Very Large Telescope Interferometer VLTI. The emission of the
dusty envelope, spectrally dispersed at a resolution of 30 from 8 to 13.5
micron, appears resolved by a single dish UT telescope. In particular the
angular diameter increases strongly within the silicate absorption band.
Moreover an acquisition image taken at 8.7 micron exhibits, after
deconvolution, a strong asymmetry. The axis ratio is 0.75+/-0.07 with the FWHM
of the major and minor axis which are 286mas and 214mas respectively. The
measured PA angle, 95 degrees +/-6 degrees is reminiscent of the asymmetry in
the OH maser emission detected at 1612MHz by Bowers & Johnston (1990) for this
star. In interferometric mode the UT1-UT3 102m baseline was employed to detect
the presence of the star. No fringes have been found with a detection threshold
estimated to be of the order of 1% of the total flux of the source, i.e. 5-8
Jy. These observations were carried out during the phase of maximum luminosity
of the star, when the dust shell is more diluted and therefore the chance to
detect the central source maximized. We modeled the dusty environment based on
the work of Justannont et al. (1996). In particular, the failure to detect
fringes provides strong constraints on the opacities in the inner regions of
the dust shell or in the close vicinity of the star.
