On the magnetic field of OH 231.8+4.2

During the transition from an AGB star to a planetary nebula, a large number of low/intermediate initial mass stars loses its spherical symmetry. The process responsible for that change of morphology is, so far, not well understood. The candidates responsible for shaping these objects are (i) a companion to the star (binary/heavy planet) and its tidal forces, (ii) disk interaction and (iii) magnetic fields - or a combination of these. In particular a binary induced magnetic field is a promising option. To study this we observed the polarization of H₂O masers in the known binary pre-Planetary Nebula (pPN) OH231.8+4.2. Our results show a magnetic field B _|| of ~45 mG is present in the H₂O maser region of this pPN.