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A. Dayal (IPAC/JPL), W.B. Latter (SIRTF Science Center/IPAC/Caltech), J.H. Bieging, D.M. Kelly (Steward Obs.), J.L. Hora (SAO), A.G.G.M. Tielens (U. Groningen)
We present 3-D spatial and kinematical models for the distribution of neutral and ionized gas in planetary and proto-planetary nebulae that are based on data from our NICMOS/HST observations. Interactions between the dense neutral envelope, the UV radiation field, and the fast stellar wind result in a menagerie of PN shapes, many of which include strong asymmetries. One of our NICMOS targets is the hot young PN, NGC 7027. Images that isolate H2 emission show two bright intersecting rings, which we interpret as brightened rims of an inclined biconical structure. This structure encloses the roughly elliptical ionized region. Our models mimic very well the observed structure of this object, and reveal the 3-D characteristics of the photodissociation front and ionized core. The structures seen in molecular hydrogen emission and in tracers of the ionized core appear different and spatially distinct. This type of two component morphology is seen in several of our NICMOS targets. We discuss discrepancies between the data and models; these differences provide additional information about the detailed structure of the nebula. Details of the modeling and results are discussed, including the effect of orientation on our perception of nebular appearance for the inferred 3-D structures. Additional ground-based observing programs, including velocity structure measurements and mid-infrared imaging, are providing further constraints.
This work is part of a detailed study into the evolution of circumstellar material exposed to strong and time-variable ultraviolet radiation fields. It is supported by a NASA Long Term Space Astrophysics Program grant and Hubble Space Telescope General Observer grants.