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D. Hamacher, S. Eyermann, A. K. Speck (University of Missouri - Columbia), M. Meixner (Space Telescope Science Institute)
Planetary Nebulae (PNe) represent the final phase of evolution for intermediate mass stars, and are major contributors to the enrichment of the interstellar medium (ISM). In PNe, a hot central star illuminates a gas and dust shell which was ejected during earlier evolutionary phases. A better understanding of the nature of the molecular and ionized gas envelopes of PNe is important to our understanding of the evolution of PNe and their contribution of heavy elements and dust to the ISM. Knots and filaments in the ionized gas images of PNe are common, if not ubiquitous. For a few PNe, it has been shown that these knots coincide with the molecular gas, suggesting that molecules exist inside dense condensations within the ionized regions. The origins of these clumps are not known. We present a preliminary study of the morphologies of both molecular and ionized gas for four PNe that have been imaged by both WFPC2 and NICMOS (in the 2.12\mum H2 line). We compare structure and appearance of the knots as seen in ionized and molecular gas for each PNe in order to gain a better understanding of the nature of these knots. Furthermore, the knots in different nebulae are compared to assess the effect of the evolutionary status of the whole PN on the the structure and appearance of the knots. This study will aid in our understanding of the origin of the molecular knots, as well as the enrichment of the ISM by dying intermediate mass stars.
Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.