Multiple Collimated Outflows in the Proto-planetary Nebula GL 618

Abstract

We present narrow-band H-alpha, [S II], and [O I] Hubble Space Telescope images of the young planetary nebula GL 618. This object is a compact, bipolar nebula that is currently undergoing the transition from asymptotic giant branch star to planetary nebula. Our images confirm the presence of at least three highly collimated outflows emanating from the central regions of GL 618. We also detect H-alpha emission close to the central dust lane and in an extended scattered light halo. The three outflows are occurring simultaneously in this object, as opposed to being the result of a precessing jet. We derive an inclination for the brightest outflow in the East lobe of 39 degrees. This differs from the previous estimate of 45 degrees. In addition, our results indicate that the outflows seen in GL 618 are probably not coplanar. Line strengths derived from the narrow-band images indicate a shock velocity in the range of 40 - 100 km/s. Based on the shock velocity we estimate that the age of the outflows is less than 500 years. The outflows seen in the optical images of GL 618 are related to features seen in near-IR, CO and CS maps of this object. This relationship indicates that the outflows are playing a major role in the morphological evolution of this young planetary nebula, interacting with and shaping the neutral envelope surrounding GL 618. We discuss the implications of these jets and their interaction with the neutral envelope in the context of current models of planetary nebula formation.