2002A&A...385..205G

We present hydrodynamical models of planetary nebulae with detached binary cores. The models are obtained according to the interacting winds scenario. Slow AGB wind models are produced by means of 3-D SPH simulations. The SPH results provide initial conditions for the evolution of a fast and rarefied wind injected into the AGB wind. In close binaries the density distribution of the slow wind is significantly modified by the gravity of the secondary, resulting in an enhanced density region close to the orbital plane of the system, and low density regions elongated perpendicularly to the orbital plane (we refer to those effects as gravitational focusing). The fast wind propagating through such a medium naturally develops a bipolar structure. In wider binaries the effect of gravitational focusing is weaker, and elliptical nebulae are produced instead of bipolar ones. In binaries wider than ∼10AU the effect becomes unimportant, and the resulting nebulae are almost entirely spherical apart from local corrugations caused by hydrodynamical instabilities. Thus, gravitational focusing alone is capable of generating a broad range of morphologies (from nearly spherical to strongly bipolar). The results are discussed in relation to nebulae associated with symbiotic stars.