VLBA H2O and SiO maser observations in the pPN OH 231.8+4.2

We report high-resolution observations of H₂O, 6_1,6−5_2,3 and ²⁸SiO v=2, J=1-0 maser emissions obtained with the Very Long Baseline Array in the bipolar pre-planetary nebulae OH 231.8+4.2 (see Desmurs et al., 2007). A phase referencing technique was used to recover the absolute position of both emissions. We detected two groups of water vapour emission oriented nearly north-south. SiO masers are tentatively found to be placed between the two H₂O maser emitting regions.