Molecular abundance enhancements in the highly collimated bipolar outflow BHR 71

We report observations of the J = 3 --> 2 and J = 2 --> 1 transitions of Si O and CS, the J(k) = 3(k) --> 2(k) and J(k) = 2(k) --> 1(k) transitions of CH3OH, and the J = 1 --> 0 transition of HCO+, made with Swedish-ESO Submil limetre Telescope (SEST), toward the highly collimated bipolar outflow BHR 71. Broad wing emission was detected toward the outflow lobes in all the ob served molecular lines. The shapes of the profiles are strikingly different from molecule to molecule. For CS and HCO+ the emission from the outflowin g gas appears as a weak broad feature superposed upon a strong narrow emiss ion from the quiescent ambient gas. For CH,OH the intensity of the broad em ission feature is considerably stronger than that of the narrow component, whereas for SiO the broad feature completely dominates the emission spectra . The spatial distribution of the integrated wing emission is considerably extended and broadly similar in all the observed molecular transitions, sho wing well-separated blueshifted and redshifted lobes with FWHM angular size s of 2'.4 x 1'.3 and 2'.4 x 1'.4, respectively. We find that the abundance of methanol and silicon monoxide in the outflow lobes is enhanced with resp ect to that of the ambient cloud by factors of up to similar to 40 and 350, respectively. The large enhancements of methanal and silicon monoxide in t he outflow lobes are most likely due to the release from grains of ice mant les and Si-bearing species via shocks produced by the interaction between t he outflow and dense ambient gas. On the other hand, we find that the abund ance of HCO+ in the outflowing gas is smaller than that in the ambient gas by about a factor of 20, a decrease consistent with theoretical predictions of shock models.