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2001MNRAS.322..280Z - Mon. Not. R. Astron. Soc., 322, 280-308 (2001/April-1)
Bipolar outflows in OH/IR stars.
ZIJLSTRA A.A., CHAPMAN J.M., TE LINTEL HEKKERT P., LIKKEL L., COMERON F., NORRIS R.P., MOLSTER F.J. and COHEN R.J.
Abstract (from CDS):
A model is presented consisting of an outer AGB wind which is swept up by a faster post-AGB wind, with either the AGB or post-AGB wind being non-spherically symmetric. The interface of the two winds is shown to exhibit a linear relation between velocity and distance from the star, giving the impression of an accelerating outflow. The OH data confirm the predicted linear velocity gradients, and also reveal torus-like, uniformly expanding components.
All sources are discussed in detail using optical/HST images where available. ISO data for Roberts 22 reveal a chemical dichotomy, with both crystalline silicates and PAH features being present. IRAS 16342-3814 shows a dense torus with mass 0.1M☉ and density of 108cm–3; HST data show four point-like sources located symmetrically around the nebula, near the outer edge of the dense torus.
Lifetimes for the bipolar OH/IR stars are shown to be in excess of 104yr, longer than normal post-AGB time-scales. This suggests that the toruses or discs are near-stationary. We suggest that accretion from such a disc slows down the post-AGB evolution. Such a process could explain the link between the long-lived bipolar nebular geometry and the retarded star.
Abstract Copyright: The Royal Astronomical Society
Journal keyword(s): masers - stars: AGB and post-AGB - planetary nebulae: general - infrared: stars
Simbad objects: 52
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