2007BaltA..16...87M

We have observed a bipolar post-AGB star OH 231.8+4.2, using the mid-infrared interferometer MIDI and the infrared camera with an adaptive optics system NACO on VLT. An unresolved core (<200 mas in FWHM), found at the center of the OH231.8+4.2 in the 3.8 µm image, is resolved with the interferometer. The fringes from the four baselines consistently show the presence of a compact circumstellar shell with an inner radius of 30-40 mas, which is equivalent to 40-50 AU at 1.3 kpc. The measured size of the circumstellar feature is consistent with the size of disks calculated by hydrodynamic models, implying the circumstellar feature may have a disk configuration. The mid-infrared size of the circumstellar dust shell or disk among AGB and post-AGB stars seems to be correlated with the effective temperature of the central star.