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C. Sanchez Contreras (Caltech), R. Sahai (JPL/Caltech)
Astronomers have long been puzzled by the morphological variety and bizzare shapes of planetary and pre-planetary nebulae (PNe and PPNe). Nowadays, an increasing number of astronomers believe that fast jet-like outflows ejected in the PPN phase are responsible for carving out the diverse shapes in the dense envelopes of their progenitor AGB stars. However, finding direct observational evidence for these elusive post-AGB jets is very difficult since they are thought to be compact, tenuous, and to operate only for a very short period of time (less than 1000yr). Also, a main difficulty in observing the jets directly is the presence of the dense ambient circumstellar material with which they interact.
Recently, HST/STIS observations have allowed for the first time the direct study of the elusive post-AGB winds in one PPN, He3-1475 (Sanchez Contreras & Sahai 2001). Those winds have been discovered through blue-shifted absorption features in the Balmer and other recombination lines arising from the inner <0.7arcsec of the nebula. Such features are spatially and spectrally resolved in the STIS data, allowing us to study the spatio-kinematic structure of the winds. Here we present a comprehensive study of the STIS spectra for the whole set of slits and gratings available for He3-1475. Our detailed analysis of the STIS data (in progress) includes improved estimates, and spatio-kinematical modeling, of the Halpha optical depths for all the slits and characterization of the physical conditions in the absorbing gas by comparing optical depths in different lines. Such an analysis is need to tightly constrain the physical properties of the post-AGB jets and, ultimately, to understand their origin.
Support for Proposal number AR-09554.03 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.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.