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R. Sahai (Jet Proplusion Laboratory/ Caltech), C. Sanchez Contreras (Caltech)
The impact of fast, collimated jets on the spherical, slowly expanding circumstellar envelopes of AGB stars, is believed to be responsible for the remarkable bipolarity and high axial-velocities observed in most post-AGB objects (protoplanetary and planetary nebulae). From an analysis of spatially-varying H\alpha absorption line features in (archival) STIS long-slit spectra, we recently discovered very fast (upto 2300 km/s) collimated outflows in the prototype protoplanetary nebula, He3-1475 (Sánchez Contreras & Sahai 2001, ApJ, 553, L173).
Here, we report results from a similar analysis of STIS spectra of the post-AGB object, HD44179 (also known as the Red Rectangle because of its red colors and rectangular morphology). Unlike He3-1475, the H\alpha absorption line profile (relative to the continuum) does not show strong changes along the slit, indicating that both the continuum and the absorption arise near or from the central star; we are mostly seeing the stellar spectrum reflected off dust in the nebula. In contrast, the H\alpha emission profile does change significantly along the slit, indicating its origin in a spatially resolved (although compact) region around the star. The clear velocity gradient in this inner region (the emission from the north/south lobe is blue-/red- shifted) indicates a bipolar outflow with a speed greater than or about 65 km/s. This is the first time that this inner, bipolar outflow is seen in this object and the first time that (given the unusual proximity of HD44179 at 380 pc) observations enable us to study the post-AGB wind as close as 40 AU from the central star. The expansion age of the outflow material in its innermost regions is only 3 yrs. The velocity of this outflow decreases with distance beyond +/-0".2 (75 AU). Unravelling the complex structure and kinematics of the outflow suggested by this behaviour will require detailed modeling (in progress), but should yield important insights into the physical properties of the fast post-AGB outflow in HD44179.
The author(s) of this abstract have provided an email address for comments about the abstract: sahai@jpl.nasa.gov
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.