NEAR-INFRARED AND ULTRAVIOLET SPECTROPHOTOMETRY OF THE YOUNG PLANETARY-NEBULA HUBBLE-12

In this paper we present spectrophotometry from 0.84-1.32 mum of the young planetary nebula Hubble 12. Archival IUE observations are rereduced and presented as well. Features of the infrared spectrum are catalogued and compared with those of other planetary nebula. Of these features the most peculiar is the brightness of the O I lines. O I lambda13164 is stronger in Hubble 12 than in any other planetary nebula yet measured. The presence of lambda13164 indicates that fluorescent excitation by the stellar continuum is the principal mechanism generating the O I lines. Their unusual strength probably results from the abundance of neutral material in the system. Fluorescently excited H-2 features, detected by Dinerstein et al [ApJ, 327, L27 (1988)] in measurements of the circumnebular neutral gas, are not apparent in our observations of the more central, ionized regions. The IR measurements are combined with the UV data and published optical observations to provide several independent determinations of the extinction, the electron density, and the electron temperature. Our best value for the extinction is E(B - V) =0.85, about 0.45 of which is probably interstellar in origin. The different emission lines indicate densities which range from a few thousand up to 10(6) cm-3 for the ionized regions, with values Up to 10(7) cm-3 being possible for the neutral zones. The [O III] lines indicate an electron temperature of less-than-or-equal-to 10 000 K, somewhat lower than the value suggested by the continuum emission from the ionized gas. The range in extinction, density, and temperature suggests that within the ionized region, pockets of emission with distinctly different conditions exist. The logarithmic abundances for helium, oxygen, and sulfur are found to be 11.11, 8.34, and 6.61, respectively.