Three-dimensional structure of the circumstellar envelope of CRL 618 based on the CO-13 J = 1-0 mapping observations

The circumstellar envelope of the carbon-rich star CRL 618 has been mapped by the CO-13 J = 1-0 transition with a resolution of about 5.0 sec x 4.3 sec with the Nobeyama Millimeter Array. Emission is extended in size by about 10 sec, and the distribution is approximately spherical. No strong elongation of CO-13 features along or perpendicular to the bipolar axis has been observed. Combining with the CO-12 J = 1-0 data that were taken before, we have created three-dimensional density and temperature profiles of the CRL 618 circumstellar envelope. For creating the three-dimensional model, it is assumed that the expansion velocity is constant and the large-velocity-gradient model is applicable. The former CO-12 observations show that the envelope of CRL 618 consists of complex features. On the basis of the present CO-13 observations, these features are interpreted as the temperature and density irregularities in the outer circumstellar shell. The comparison of the present results with the model density profile given by optical light-scattering maps is made.