The “Twin Jet” Planetary Nebula M2‐9

We present a model for the structure, temporal behavior, and evolutionarystatus of the bipolar nebula M2-9. According to this model the system consistsof an AGB or post-AGB star and a hot white dwarf companion, with an orbitalperiod of about 120 years. The white dwarf has undergone a symbiotic novaeruption about 1200 years ago, followed by a supersoft x-ray source phase. Thepositional shift of the bright knots in the inner nebular lobes is explained interms of a revolving ionizing source. We show that the interaction between theslow, AGB star's wind, and a collimated fast wind from the white dwarf clears apath for the ionizing radiation in one direction, while the radiation isattenuated in others. This results in the mirror-symmetric (as opposed to themore common point-symmetric) shift in the knots. We show that M2-9 provides animportant evolutionary link among planetary nebulae with binary central stars,symbiotic systems, and supersoft x-ray sources.Comment: 13 pages + 2 figures. Submitted to Ap