Images of Uranus' Near-IR H_3(+) and H_2 Emissions

Details Images of Uranus' Near-IR H_3(+) and H_2 Emissions Images of Uranus' Near-IR H_3(+) and H_2 Emissions

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...19311604t&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #116.04; Bulletin of the American Astronomical Society, Vol. 30, p.1423

Astronomy and Astrophysics

Astronomy

Scientific paper

Uranus is the only major planet with a prominent hot, extended H corona. Near-infrared spectra of Uranus show substantial global ionospheric H_3(+) and thermospheric H_2-quadrupole emission with rotational temperatures varying between extremes of 600 and 900 K. Our previous spectra have indicated that hot H_2 emits above the limb as high as 7% of the planet's radius and that H_3(+) along the central meridian may be more concentrated towards the center of the disk than is H_2. Non-auroral emissions appear to dominate Uranus' near-IR emission spectrum, in contrast to the case for Jupiter. Uranus' magnetic pole is tilted 60 deg relative to the spin axis, so the auroral emissions should be detectable against the background emissions through modulation by the planet's rotation. Voyager UVS detected spatially localized UV auroral H_2 emission near both magnetic poles. However, the FUV observations of IUE, Voyager, and HST so far been ambiguous regarding the strength of Uranus' auroral activity. A powerful method to separate auroral from non-auroral emissions and to study the excitation processes of the latter is spatial imaging of the emissions. Using NSFCam at the IRTF on July 25-28, 1998, we obtained rotationally-resolved narrow-band images of Uranus' near-IR H_3(+) and H_2 emissions. These images reveal spatial variations over the disk for both species which vary with rotational phase. They are expected to help elucidate the aurora and the hot corona-hot thermosphere connection. We report preliminary results from these images. These include an investigation of time-of-day (i.e. solar zenith angle) effects by comparing and contrasting morning and evening limb emissions; inferring the role of solar EUV in exciting H_3(+) and governing its distribution over the disk; determining the vertical distribution and scale height of H_2; and investigating the hemispherical IR auroral power output.

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