High-resolution observations at lambda=3 mm of the OH 231.8+4.2 molecular outflow

We present high spatial resolution observations of HCO+ (J = 1-0), SO(J = 2 (2) - 1(1)), (HCN)-C-13 (J = 1-0), SiO (nu = 1, J = 2-1), and the continuum at 3mm from OH 231.8 + 4.2, taken with the IRAM interferometer at Plateau de Bure. We also report the first detection of NS in circumstellar envelope s. The overall distribution of the emission of all molecules (except for HC O+ and the SiO maser) is similar to that of CO. The most intense emission a rises from a compact, slowly-expanding component around the central star. T he rest of the emission comes from gas distributed in a narrow region along the symmetry axis, that flows outwards following a velocity gradient also similar to that found in CO. Our observations show with high accuracy the d istribution of the HCO+ intensity, that is found to be very clumpy and stro ngly enhanced in the shock-accelerated lobes. We argue that such a distribu tion is due to the efficient formation of this molecule by shock-induced re actions. An expanding disk or ring around the central star is detected from the SO emission. The characteristic radius and expansion velocity of this structure are 2 10(1)6 cm and 6-7 km s(-1) respectively. The SiO maser emis sion could arise from the innermost parts of such a disk. The 3 mm continuu m emission seems to be due to cold dust (similar to 20 K) distributed in th e lobes of OH 231.8 + 4.2 as well as from warmer (similar to 55 K) dust loc ated in a compact region surrounding the central star.