Spectro-imaging observations of Jupiter's 2-μm auroral emission.: I.: H3+ distribution and temperature

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 mum, combined with high spectral resolution (0.2 cm(-1)), allowed us to map emission from the H-2 S-1(1) quadrupole line and from several H-3(+) lines. The H-2 and H-3(+) emission appears to be morphologically different, especially in the north, where the latter notably exhibits a hot spot near 150degrees-170degrees System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform H-2 S-1 (1) emission. We also present the first images of the H-2 emission in the southern polar region. The spectra include a total of 14 H-3(+) lines, including two hot lines from the 3nu(2)-nu(2) band, detected on Jupiter for the first time. They can be used to determine H-3(+) column densities, rotational (Trot) and vibrational (T-vib) temperatures. We find the mean T-vib of the nu(2) = 3 state to be lower (960 +/- 50 K) than the mean T-rot in nu(2) = 2 (1170 75 K), indicating an underpopulation of the nu(2) = 3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from nu(2) observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, T-vib and column densities, indicates that variations in line intensities are mostly due to correlated variations in the H-3(+) column densities. The thermostatic role played by H-3(+) at ionospheric levels may provide an explanation. The exception is the northern hot spot, which exhibits a T-vib about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the H-2 and H-3(+) emission are equally difficult to explain. (C) 2004 Elsevier Inc. All rights reserved.