DETECTION OF SIO EMISSION IN THE L1157 DARK CLOUD

Intense thermal emission lines of SiO (upsilon = 0, J = 1-0 and 2-1) are detected in a low-mass star-forming region, L1157. The emission is confined to a compact region toward the blue lobe of the CO outflow, where shock heating due to interaction between the outflow and dense gas has been found. In contrast, the emission of SiO is not detected toward the IRAS source and the red lobe. The distribution of SiO is different from that of CS; the intense CS line is observed in the vicinity of the IRAS source. The peak fractional abundance of SiO is estimated to be about 10(-7). This value is higher than a typical upper limit in quiescent dark clouds by a factor of approximately 10(4). These results suggest that SiO is produced in the shocked region probably through grain destruction processes.