Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line

TL;DR

This study presents interferometric observations of the proto-planetary nebula CRL 618 in multiple CO lines, revealing details about its molecular structure, emission regions, and dust continuum, with implications for its physical conditions.

Contribution

First interferometric detection of 12CO J=6-5 and 13CO J=2-1 lines in CRL 618, providing new insights into its molecular and dust emission properties.

Findings

High velocity component flux is fully recovered in 12CO J=6-5

Low velocity component emission is largely extended and resolved out

Cavity structure is not clearly detected in 12CO J=6-5, indicating asymmetry

Abstract

We report on the results of a Submillimeter Array interferometric observation of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new capability of 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 first interferometrically observed 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 both at 230 and 690 GHz. The flux of the 690 GHz continuum emission seems to be partially resolved out, suggesting 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 axial symmetric.