[Previous] | [Session 36] | [Next]
L.M. Trafton (U. Texas), S. Miller (UCL), T.R. Geballe (Gemini)
During observations on 3-5 May 1993 of Uranus’ near-IR spectrum, which highlights emission lines of H2 and H3+ from the planet’s hot thermosphere and ionosphere, a single case of prominent hot H2 emission was noted. Both the intensity and temperature were elevated significantly compared to other observations made during the 1992-1995 period, including the May 1993 observing run. It was suggested (Trafton et al. 1999) that this may have been a detection of Uranus’ aurora passing through the spectroscopic slit, against the global background of thermal emission from the hot thermosphere. The slit was set along the planet’s central meridian. Owing to the large sub-Earth latitude (-56 deg) and the low latitude of Uranus’ fragmented auroral arc (due to the 60 deg tilt of the offset magnetic pole), the aurora would lie close to the limb and likely be enhanced by the secant path. The 3”x3” pixel was too large to confirm an auroral origin on the basis of spatial localization. Other candidate sources are a solar energetic particle event or a magnetospheric instability resulting in temporarily enhanced charged-particle precipitation.
We report results from an observing run at the IRTF/SpeX on July 21, 2002, recently past solar maximum, in which we observed an enhancement of the rotational temperature of Uranus' upper-atmospheric H2 based on the Q-branch emission at 2.42 microns. This may constitute the second detection of a prominent hot-emission event. Unlike the first event, however, the sub-Earth latitude was only –20 deg so that a detected aurora would not lie close to the limb, or be significantly enhanced by the secant. For this event, the pixel size was much smaller (0.”15), allowing the spatial distribution of the emission to constrain hypotheses for the source mechanism. Results of our analysis will be presented.
If the author provided an email address or URL for general inquiries,
it is as follows:
Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.