Toward Understanding the Bipolar Geometries of Preplanetary Nebulae with High-Velocity Polar Flows

Details Toward Understanding the Bipolar Geometries of Preplanetary Nebulae with High-Velocity Polar Flows Toward Understanding the Bipolar Geometries of Preplanetary Nebulae with High-Velocity Polar Flows

Jul 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001hst..prop.9101s&link_type=abstract

HST Proposal ID #9101

Physics

Hst Proposal Id #9101 Ism And Circumstellar Matter

Scientific paper

Most planetary nebulae {PNs} show bipolar morphology, in striking contrast to the largely round shapes of the circumstellar envelopes of the AGB stars from which they evolve. Several lines of evidence, including high spatial- resolution imaging with HST, suggest that high-velocity collimated outflows occuring during the transition from AGB to the PN phase - the preplanetary nebula {PPN} phase - are significant agents for imposing bipolarity on the circumstellar environment. Unfortunately, kinematic data at a comparable spatial resolution has been lacking, limiting our understanding of the physical mechanisms responsible for the bipolarity. We have therefore begun a multiwavelength program, including interferometric spectral-line imaging in the radio and HST imaging, to study PPNs in detail. We find, for two bipolar PPN, that the spatio-kinematic distribution of the OH masers relative to the HST optical structure is consistent with the hypothesis that the optical lobes result from a fast outflow interacting with the slow, dense AGB wind, producing an increasing radial velocity from the equator to the poles. We propose imaging of 17 PPNs with WFPC2 for comparison with high-resolution spectral-line images {being obtained with VLA/MERLIN/ATCA}, enabling us to test this hypothesis, and to understand the fast outflow and how its hydrodynamical interaction with the AGB wind produces a bipolar nebula.

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