H-2 Imaging of Three Proto-Planetary and Young Planetary Nebulae

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High-resolution (0."15) 2.12 mum H-2 and narrowband K images have been obtained of one cool proto - planetary nebula, IRAS 20028+3910, and two hot proto - planetary/young planetary nebulae, IRAS 19306+1407 and IRAS 22023+5249. The observations were made with an adaptive optics system and near-infrared imager on the Gemini North 8 m telescope. All three nebulae are seen to be extended, and in two and possibly all three of them H-2 is found to be emitting from bipolar lobes. In IRAS 19306+1407, H-2 emission is seen arising from a ring close to the star and from the edges of emerging bipolar lobes. In IRAS 20028+3910, one bright lobe and a very faint second lobe are seen in the H-2 and K-band images, similar to the published visible images, but in the H-2 and K-band images a faint filament appears to connect the two lobes. The central star is not seen in IRAS 20028+3910, indicating that the nebula is optically thick even at 2 mum, which is unusual. The images suggest that extended H2 emission is often the manifestation of fast-slow wind interactions in the bipolar lobes.