Molecular Hydrogen Emission from Young Planetary Nebulae

Recent observations of molecular hydrogen emission in the planetary nebulae J900, BD+30deg 3639, and IRAS 21282+5050 are presented. Imaging observations of J900 were made in broadband J, H, and K, and narrowband 2.122 microns (for H_2 1-0 S(1)), Brackett-gamma , and continuum filters. The H_2 images reveal a remarkable set of outward-extending features, which are probably excited either by oblique shocks caused by material ejected from the nebula, or by radiation leaking from holes in the opacity surrounding the ionized gas. In the inner nebula, the H_2 emission, Brackett-gamma emission, and underlying continuum are spatially resolved, and their relative positions indicate an ionization front seen edge-on. A position-position-velocity ``data cube'' of the H_2 1-0 S(1) line emission from BD+30deg 3639 was constructed from a series of R=lambda /delta lambda =6000 spectra. The H_2 emission is distributed in blue- and red-shifted lobes with velocities shifted from the ionized gas by up to +/-50 km s(-1) . We have also obtained an R=1000 spectrum covering the entire K band which spatially resolves the ionized ring and H_2 lobes. The excitation of the molecular hydrogen emission is discussed. We report the clear detection of the H_2 1-0 S(1) 2.122 microns line in an R=6000 spectrum of IRAS 21282+5050. The slit was oriented along the edge-on dust torus seen in mid-infrared and 3.3microns images, and the spatial profile of the H_2 emission follows that of the dust emission. Infrared astronomy at Palomar Observatory is supported by grants from the NSF and NASA.