The "water-fountain nebula" IRAS 16342-3814: Hubble Space Telescope/very large array study of a bipolar protoplanetary nebula

We present Hubble Space Telescope (HST) Wide-Field and Planetary Camera 2 i mages and VLA OH maser emission-line maps of the cold infrared object IRAS 16342-3814, believed to be a protoplanetary nebula. The HST images show an asymmetrical bipolar nebula, with the lobes separated by a dark equatorial waist. The two bright lobes and the dark waist are simply interpreted as bu bble-like reflection nebulae illuminated by starlight escaping through pola r holes in a dense, flattened, optically thick cocoon of dust, which comple tely obscures the central star A faint halo can be seen surrounding each of the lobes. The bubbles are likely to have been created by a fast outflow ( evidenced by H2O emission) plowing into a surrounding dense, more slowly ex panding, circumstellar envelope of the progenitor asymptotic giant-branch ( AGB) star (evidenced by the halo). The IRAS fluxes indicate a circumstellar mass of about 0.7 M-.(D/2 kpc) and an AGE mass-loss rate of about 10(-4) M , yr(-1) (V-exp/15 km s(-1))(D/2 kpc)(2) (assuming a gas-to-dust ratio of 2 00). OH features with the largest redshifted and blueshifted velocities are concentrated around the bright eastern and western polar lobes, respective ly, whereas intermediate-velocity features generally occur at low latitudes , in the dark waist region. We critically examine evidence for the post-AGE classification of IRAS 16342-3814.