2007AJ....134.2035N

We report on the results of a Submillimeter Array (SMA) interferometric observation of the proto-planetary nebula CRL 618 in the ¹²CO J=6-5 line. With the new capability of the SMA enabling us to use two receivers at a time, we also observed simultaneously in the ¹²CO J=2-1 and ¹³CO J=2-1 lines. The ¹²CO J=6-5 and ¹³CO J=2-1 lines were interferometrically observed for the first time toward CRL 618. The flux of the high-velocity component of the ¹²CO J=6-5 line is almost fully recovered, while roughly 80% of the flux of the low-velocity component is resolved out. The low recovery rate suggests that the emission region of the low-velocity component of the ¹²CO J=6-5 line is largely extended. Continuum emission is detected at both 230 and 690 GHz. The flux of the 690 GHz continuum emission seems to be partially resolved out, suggesting that dust emission partly contaminates the 690 GHz continuum flux. The cavity structure, which has been confirmed in a previous observation in the ¹²CO J=2-1 line, is not clearly detected in the ¹²CO J=6-5 line, and only the south wall of the cavity is detected. This result suggests that the physical condition of the molecular envelope of CRL 618 is not exactly axially symmetric.