High resolution K-S polarization mapping of OH 231.8+4.2 (OH 0739-14) withSOFI

The bipolar reflection nebula OH 231.8 + 4.2 (OH 0739-14) centred-on the Mi ra variable star QX Pup has been mapped at Ks in linear polarization using the ESO SOFI near-infrared multi-mode instrument. The large scale linear po larization features agree with previous studies, validating the polarimetri c mode of the instrument. However the high spatial resolution of the polari zation map reveals considerable structure, some of which finds corresponden ce in the surface brightness images. The core is crossed by low polarizatio n filaments. the northern lobe reveals an axial finger and a rim of very hi gh linear polarization (upto 80%) whilst the southern lobe shows less polar ization contrast. There is a trend in polarization perpendicular to the bip olar axis in both lobes. The individual linear polarization features most p robably arise from localised dust structures with distinct orientations lea ding to differing polarization through single scattering. A single scatteri ng geometric model, consisting of two lobes of ellipsoidal section and a ce ntral dense disk, is considered which can explain the general features of t he intensity and polarization images.