We report interferometric observations of the SiO (2-1) and CO (1-0) lines toward the blueshifted lobe of the L1157 bipolar outflow. These observations reveal clumpy SiO emission aligned with highly collimated CO emission. The SiO emission is enhanced in two prominent condensations, similar to those seen in VLA images of the NH_3(3, 3) line. The SiO condensation closer to the outflow source peaks within 10″ of a bright knot of the 2.1 μm H_2 line emission and shows blueshifted emission extending more than 17 km s~(-1) from the cloud velocity. The close association between the SiO and H_2 emission suggests that the SiO emission is excited in the accelerated postshock regions near the head of an underlying jet. The SiO condensation farther downstream shows a smaller velocity extent and no apparent associated H_2 emission. We suggest that the two condensations result from separate interactions of an episodic jet with the surrounding cloud core. In this scenario, the emission region farther downstream results from an older event. Both SiO condensations appear to lead the high-velocity CO emission, consistent with the idea that SiO emission is excited close to the head of the jet and the CO accelerated in the oblique outer wings of the bow shock.
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机译：我们报告SiO（2-1）和CO（1-0）线向L1157双极流出的蓝移波瓣的干涉观察。这些观察结果表明结块的SiO排放与高度准直的CO排放一致。类似于两个NH_3（3，3）线的VLA图像中看到的那样，SiO的排放在两个明显的缩合中得到增强。靠近流出源的SiO凝结在2.1μmH_2线发射的明亮结的10''内达到峰值，并显示出从云速延伸超过17 km s〜（-1）的蓝移发射。 SiO和H_2排放之间的密切联系表明SiO排放在下面的喷头附近的加速后震荡区域受到激发。下游的SiO凝结显示出较小的速度范围，没有明显的H_2排放。我们认为，这两种凝结是由间歇性射流与周围云芯的单独相互作用引起的。在这种情况下，下游区域的发射区域是较旧事件的结果。两种SiO的凝结似乎都导致了高速CO的排放，这与SiO的排放在射流头附近被激发并且CO在弓形激波的倾斜外翼中加速的想法一致。
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