The Nature and Origin of Molecular Knots in Planetary Nebulae

doi:10.1063/1.2146252Planetary Nebulae (PNe) are major contributors to the enrichment of the interstellar medium (ISM). Knots and filaments in the ionized gas images of PNe are common, if not ubiquitous. Additionally, it has been shown that molecular gas exists inside dense condensations within the ionized regions. The origins of these clumps are not known, though the suggested formation mechanisms fall into two main scenarios: (1) they form during the AGB phase; (2) they form as a result of the onset of the PN phase as the fast wind ploughs into the slower moving AGB wind. The currently favored model is that the knots are formed by the onset of the PN phase and then sculpted as the ionizing radiation penetrates deeper into the circumstellar envelope. We present preliminary results of a study which compares the morphologies of molecular and ionized gas emission in several PNe, covering a range of ages.This work was supported by several funding agencies: SE and AS were supported by HST-AR- 10686, and by the Research Council of University of Missouri - Columbia. MM and PM were supported in part by HST-GO-01041 and by the internal STScI funds, DDRFD0001.82319. Support for Program numbers HST-AR-10686 and HST-GO-01041 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555