Massive expanding torus and east outflow in planetary nebula NGC 6302

Abstract

We present interferometric observations of 12CO and 13CO J = 2-1 emission from the butterfly-shaped, young planetary nebula NGC 6302. The high angular resolution and high sensitivity achieved in our observations allow us to resolve the nebula into two distinct kinematic components: (1) a massive expanding torus seen almost edge-on and oriented in the north-south direction (roughly perpendicular to the optical nebula axis), which exhibits very complex and fragmented structure; and (2) high-velocity molecular knots moving at more than 20 km s-1 and located in the optical bipolar lobes. These knots show a linear position-velocity gradient (Hubble-like now), which is characteristic of fast molecular outflow in young planetary nebulae. From the low but variable 12CO/13CO J = 2-1 line intensity ratio, we conclude that the 12CO J = 2-1 emission is optically thick over much of the nebula. Using the optically thinner line 13CO J = 2-1, we estimate a total molecular gas mass of ∼0.1 M⊙, comparable to the ionized gas mass; the total gas mass of the NOC 6302 nebula, including the massive ionized gas from the photon dominated region, is found to be ∼0.5 M⊙. From radiative transfer modeling, we infer that the torus is seen at an inclination angle of 75° with respect to the plane of the sky, and is expanding at a velocity of 15 km s-1. Comparison with recent observations of molecular gas in NGC 6302 is also discussed. © 2008. The American Astronomical Society. All rights reserved.