Extended Structures of Planetary Nebulae Detected in H<SUB>2</SUB> Emission

We present narrowband near-infrared images of a sample of 11 Galactic planetary nebulae (PNe) obtained in the H<SUB>2</SUB> 2.122 μm and Brγ 2.166 μm emission lines and the K <SUB>c</SUB> 2.218 μm continuum. These images were collected with the Wide-field Infrared Camera on the 3.6 m Canada─France─Hawaii Telescope (CFHT); their unprecedented depth and wide field of view allow us to find extended nebular structures in H<SUB>2</SUB> emission in several PNe, some of these being the first detection. The nebular morphologies in H<SUB>2</SUB> emission are studied in analogy with the optical images, and indication of stellar wind interactions is discussed. In particular, the complete structure of the highly asymmetric halo in NGC 6772 is witnessed in H<SUB>2</SUB>, which strongly suggests interaction with the interstellar medium. Our sample confirms the general correlation between H<SUB>2</SUB> emission and the bipolarity of PNe. The knotty or filamentary fine structures of the H<SUB>2</SUB> gas are resolved in the inner regions of several ring-like PNe, also confirming the previous argument that H<SUB>2</SUB> emission mostly comes from knots or clumps embedded within fully ionized material at the equatorial regions. Moreover, the H<SUB>2</SUB> image of the butterfly-shaped Sh 1-89, after removal of field stars, clearly reveals a tilted ring structure at the waist. These high-quality CFHT images justify follow-up detailed morphokinematic studies that are desired in order to deduce the true physical structures of a few PNe in the sample. Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, and France, at the Canada─France─Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.