Hubble Space Telescope and Ground-based Imaging of the Bipolar Proto--Planetary Nebula M1-92: Evidence for a Collimated Outflow

Abstract

We present ground-based and Hubble Space Telescope narrowband images of M1-92. M1-92 is a bipolar proto--planetary nebula currently undergoing the transition from asymptotic giant branch star to planetary nebula. Previous spectropolarimetry of this object revealed that the line emission produced in the bipolar lobes is dominated by shock emission. The goal of the current observations is to determine the morphology of the shock-heated gas in order to better understand the origin of this emission. The ground-based images suggest that the shock emission is concentrated in diffuse knots in the bipolar lobes. Our high spatial resolution Wide Field Planetary Camera 2 images demonstrate that the shock emission is the result of a collimated outflow that originates near the central star and impacts the bipolar lobes. The outflow axis appears to be inclined with respect to the bipolar axis of M1-92, suggesting the presence of a precessing or wobbling jet. We discuss these findings in the context of the current models that seek to explain the planetary nebula formation process.