HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF HUBBLE-12

Spectra at H (1.6 mu m) and K (2.2 mu m) have been obtained of the you ng planetary nebula Hubble 12. The prominent features in these rich sp ectra include emission from the Brackett and Pfund series of hydrogen, [Fe II], [Fe In], Mg II, He I, and H-2. Our high-resolution spectra ( R(H) similar to 2200, R(K) similar to 3500) have revealed similar to 5 0 H-2 lines at both H and K. H-2 emission in the H window and transiti ons from levels as high as v = 12 confirm the fluorescent excitation. The large number of detected H-2 lines allows us to compare in detail the observed strengths to those predicted by models of fluorescent emi ssion. We find good agreement with models that give gas densities in t he outer regions of the nebula close to n(H) = 3.0 X 10(3) cm(-3). The surface brightness of the 1-0 S(1) line is an order of magnitude high er than that predicted by models of steady state fluorescent emission, which is possibly due to the time dependence of the emission. The hel ium emission lines are found to agree well with theoretical prediction s of helium recombination, although the blended lines at 2.11 mu m imp ly a rather high T-e similar to 2 X 10(4) K. The line ratios of seven [Fe II] and three [Fe III] emission features in the H and K windows, r espectively, are found to agree with the latest theoretical prediction s for T-e similar to 10(4) K and n(e) similar to 10(4) cm(-3). This em ission may originate in pockets of shocked material in the core of the nebula. The hydrogen emission in both the Brackett and Pfund series i s found to differ significantly from case B recombination predictions, the cause of which is as yet unexplained.