Westbrook’s Molecular Gun: Discovery of Near-Infrared Microstructures in AFGL 618

Abstract

We present high-sensitivity near-IR images of a carbon-rich proto-planetary nebula, AFGL 618, obtained with the Subaru Telescope. These images have revealed and extending farther out from the edges of the previously known bipolar lobes. The spatial coincidence between these near-IR microstructures and the optical collimated outflow structure, together with the detection of shock-excited, forbidden IR lines of atomic species, strongly suggests that these bullets and horns represent the locations from which [Fe II] IR lines arise. We have also discovered CO clumps moving at greater than 200 km s-1 at the positions of the near-IR bullets by reanalyzing the existing 12CO J = 1-0 interferometry data. These findings indicate that the near-IR microstructures represent the positions of shocked surfaces at which fast-moving molecular clumps interface with the ambient circumstellar shell.