HIGH SPATIAL-RESOLUTION MAPS OF CIRCUMSTELLAR SIC2 IN IRC+10216

In this Letter we present details of the first interferometer observations of the 4(22)-3(21) transition of SiC2 at 95.57936 GHz toward IRC +10216. We find that most of the emission from SiC2 is distributed asymmetrically in the form of a shell. In particular, the map centered at V(LSR) = -23.8 km s-1 is distributed in the form of a broken ring in which the north and southeast sides are at least 3 times brighter than the west side; the ring has a radius approximately 14" with a width unresolved by our beam. The results indicate that most of the SiC2 is produced by ion-molecule reactions in the outer envelope; however, a small amount of SiC2 originates near the photosphere.