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Astron. Astrophys. 353, L5-L8 (2000)

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5. Implications for PN shaping

The bipolar outflows that we observe in BD+30o3639 clearly play a role in shaping the nebula, and they challenge the idea that the primary shaping mechanism is that of the interacting-winds model. This is significant because BD+30o3639 is one of the more plausible cases for this model. The ionized nebula shows a ring morphology that has been modeled by Masson (1989) as a thin, ellipsoidal shell. The central star emits a powerful, fast ([FORMULA]700 km s-1) wind (Leuenhagen et al. 1996), and it is one of the rare PNe where x-rays have been detected from a hot ([FORMULA] K), diffuse plasma (Arnaud et al. 1996). Although the x-rays are not spatially resolved, they are believed to be emitted by a hot bubble that fills the inner cavity and drives the nebula dynamics.

Our observations of high velocity molecular gas cannot be explained by the simple interacting-winds model, in which a hot bubble drives the ionized shell into a slower moving, neutral envelope. More importantly, our observations show that collimated outflows or jets emanate from the central regions. The bullets are sufficiently close to the central star that their formation by focusing an isotropic wind on the scale of the ionized nebula can likely be ruled out. It is true that the mass we detect in the bullets may be relatively small, but the kinetic energy is larger because of the high velocity, and when one examines Fig. 3, it appears that a substantial part of the molecular envelope has been disturbed by bipolar interactions, either by multiple or wobbling jets. It is also possible, and even likely, that the molecular gas along the polar directions has already been cleared by related outflows.

This shaping scenario is essentially the same as seen in some other cases where the interactions are caused by much more prominent collimated outflows or jets that are easily identified from their optical or molecular emission, e.g., CRL 2688 (Cox et al. 1999a) and KjPn 8 (Forveille et al. 1998). The observations reported here open up the interesting possibility that low level jet-envelope interactions, which are hard to detect, are common, and play a wide role in PN dynamics.

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999