INTERACTION OF PLANETARY-NEBULAE WITH A MAGNETIZED ISM

We study the interaction of planetary nebulae with a magnetized inters tellar medium (ISM) and show that the ISM magnetic field cannot be ign ored in analysis of the interaction of planetary nebulae with (PNs) wi th the ISM. We show that stretching and bending of magnetic held Lines can increase the effective pressure of the ISM. In particular, near t he stagnation point of the flow of the ISM around the nebula, the ISM magnetic pressure can overcome the thermal pressure, leading to strong MHD instabilities even in isothermal flows. At early stages, when the planetary nebula outer regions are still neutral, the ISM magnetic fi eld can penetrate the nebula via ambipolar diffusion. As a result, whe n pulled downstream by the flow, the magnetic field will strip the out er layers of the nebula. The Rayleigh-Taylor and Kelvin-Helmholtz inst abilities with wavenumbers along the magnetic held lines are suppresse d. Therefore, the ISM magnetic field can break the cylindrical symmetr ical nature of the interaction.