A REMODEL OF THE ENVELOPE AROUND THE 21 μm PROTOPLANETARY NEBULA IRAS 07134+1005

Recently, the CO J = 3-2 observational result of the envelope of the 21 μm protoplanetary nebula (PPN) IRAS 07134+1005 has been reported. Assuming that the CO J = 3-2 line was optically thin, the mass-loss rate of the superwind in this PPN was found to be at least 2 orders of magnitude lower than the typical range. In order to obtain a more accurate mass-loss rate, we reexamine these data and construct a radiative transfer model to compare with the data. Also, in order to better resolve the superwind, we adopt a different weighting on the data to obtain maps at a higher resolution. Our result shows that the CO J = 3-2 emission is located slightly further away from the central source than the mid-infrared emission, probably because the material is cooler on the outer part and is thus better traced by the CO emission. At a lower resolution, however, the CO emission appeared to be spatially coincident with the mid-IR emission. Our model has two components, an inner ellipsoidal shell-like superwind with an equatorial density enhancement and an outer spheroidal asymptotic giant branch wind. The thick torus in the previous model could be considered as the dense equatorial part of our ellipsoidal superwind. With radiative transfer, our model reproduces more observed features than the previous model, and it obtains an averaged superwind mass-loss rate of ∼1.8 × 10–5 M☉ yr–1, which is typical for a superwind. The mass-loss rate in the equatorial plane is 3 × 10–5 M☉ yr–1, which is also the same as that derived before from modeling the CO J = 1-0 emission.