An Infrared Imaging Study of the Bipolar Proto–Planetary Nebula IRAS 16594−4656

High-resolution mid-infrared images have been obtained in N-band and Q-bandfor the proto-planetary nebula IRAS 16594-4656. A bright equatorial torus and apair of bipolar lobes can clearly be seen in the infrared images. The torusappears thinner at the center than at the edges, suggesting that it is viewednearly edge-on. The infrared lobes correspond to the brightest lobes of thereflection nebula seen in the Hubble Space Telescope (HST) optical image, butwith no sign of the point-symmetric structure seen in the visible image. Thelobe structure shows a close correspondence with a molecular hydrogen mapobtained with HST, suggesting that the dust emission in the lobes traces thedistribution of the shocked gas. The shape of the bipolar lobes shows clearlythat the fast outflow is still confined by the remnant circumstellar envelopeof the progenitor asymptotic giant branch (AGB) star. However, thenon-detection of the dust outside of the lobes suggests that the temperature ofthe dust in the AGB envelope is too low for it to be detected at 20 microns.Comment: Accepted by the Astrophysical Journa