Discovery of a Remarkable Point-Symmetric Proto-Planetary Nebula: Hubble Space Telescope Imaging of IRAS 04296+3429

Abstract

We present images of the proto-planetary nebula (PPN) IRAS 04296+3429 (hereafter I04296) taken with the Hubble Space Telescope Wide Field Planetary Camera 2 in two wide-band filters centered at 0.56 and 0.81 μm. We find that this object, which belongs to a class of carbon-rich PPNs with a peculiar 21 μm dust emission feature, has a striking point-symmetric morphology, with a pair of long, well-collimated lobes oriented at about 70° to an equatorial elliptical ``disklike'' structure. Although dense disklike regions have been inferred from the presence of dark lanes separating the bipolar lobes of post-asymptotic giant branch (AGB) objects, I04296 is the first to show a bounded disk directly in scattered light. The lobes and the disk appear embedded in a roughly round, faint halo with a radius at least as large as 2.8". The bipolar lobes probably result from the interaction of a collimated high-velocity bipolar outflow with the spherical progenitor AGB circumstellar envelope, which is seen as the halo. The internal structure of the lobes suggests that the bipolar outflow changes its direction with time. A simple single-scattering model of a spherical inverse-square density envelope with a dust mass-loss rate of 4×10^-8 M_solar yr^-1 provides a good fit to the scattered light in the halo at both wavelengths. The collimated lobes and point-symmetric structure in I04296 provide strong support for the jet-driven formation of aspherical planetary nebulae.