Kinematic Structure of H2and [Feii] in the Bipolar Planetary Nebula M2-9

We present high-dispersion long-slit IR spectra of the double-shell bipolarplanetary nebula M 2-9 in the emission lines [Fe II] 16435 and H2 v=1--0 S(1)21218. H2 spectra reveal for the first time the kinematic structure of theouter shell in M 2-9. Kinematics of the inner shell, traced by [Fe II],resemble those of optical lines like [N II]. [Fe II] and H2 shells haveexpansion speeds roughly proportional to distance from the star (``Hubble''flows) and share the same dynamical age of 1200--2000 yr, depending on thedistance to M 2-9. Thus, the inner ionized lobes and outer molecular lobes, aswell as the molecular torus and ``outer loops'' measured by other observers,were all formed around the same time. Consequently, their nested structurelikely arises from an excitation gradient rather than independent ejections. H2and [Fe II] emission is distributed more uniformly than [N II], and IR linesare not dominated by the moving ionization pattern like visual-wavelengthlines. We suggest that this is because IR lines of [Fe II] and H2 are excitedby relatively isotropic far-UV radiation (Balmer continuum), whereas opticallines respond to a directed rotating beam of Lyman continuum. Finally, wehighlight intriguing similarities between M 2-9 and the Homunculus of etaCarinae, despite the different central engines powering the two nebulae.Comment: comments: 16 pages, 5 Figs, Fig 1 in color, accepted by AJ (August 2005