First prove of shock-excited H2 in low-ionization structures of PNe

Stavros Akras & Goncalves R. Denise

Valongo Observatory, Brasil

We report on the first detection of near-infrared H2 line emission from the low-ionization structures (LIS) in planetary nebulae (PNe). The deepest, high-angular resolution H2 v=1-0 S(1) at 2.122 micron, and H2 v=2-1 S(1) at 2.248 micron images of K 4-47 and NGC 7662, obtained using NIRI@Gemini-N, are presented here. The H2 v=1-0/v=2-1 line ratio of K4-47 is found to vary between 4 and 8, indicating a shock interaction. The strongest of these two lines, H2 v=1-0, is also detected in several LISs at the periphery of the elliptical PN NGC 7662, but for this PN the fainter H2 (v=2-1) emission is much lower than in the K 4-47 case. The latter suggests high H2 v=1-0/v=2-1 ratio --therefore possible shock excitation. Our preliminary results provide the first direct evidence that LIS are also made of H2 gas (as previously suggested) and prove that LISs are predominantly shock-excited regions.

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