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L. M. Trafton, J. H. Lacy, M. Richter, T. K. Greathouse (U. Texas at Austin)
We report the results of spectroscopic observations of Uranus' pure-rotational H2 quadrupole lines using TEXES, the new, high-resolution, University of Texes mid-IR Echelle Spectrograph. The S(1), S(2), and S(4) lines were detected on Nov 29/Dec 1, 2000 or Sep 8-14, 2002 using this instrument at resolution R=50,000-100,000 on the IRTF. (The S(3) line was not observable because it was obscured by lines of telluric ozone, the cores of which absorb strongly in this spectral region.) These emission lines arise primarily from the hottest layers of the planet's thermosphere and so constrain models of Uranus' thermospheric structure and energy balance. Unlike observations of the vibrational quadrupole lines, they directly measure the thermal emission of H2 because most of the atmospheric H2 molecules are in the ground vibrational state, and the population of the excited vibrational states likely deviates significantly from thermal equilibrium. The 2" wide slit was oriented in the Earth's north-south direction; this corresponded to a diametrical cut across Uranus' disk that bisected the central meridian at an angle of 79-82 deg. Uranus' diameter was 3."5-3."7 with seeing better than 1". The amount of Doppler broadening of the line profiles due to the planet's rotation was small, less than 2.4 km/s. Unlike for Jupiter, the background hydrocarbon emission was negligible; this is probably a result of Uranus' relatively lower stratospheric temperature and lower eddy diffusion. We present a preliminarycomparison/contrast of the observed equivalent widths with models of Uranus' thermosphere based on the Voyager UVS stellar/solar occultation thermal structures.
The author(s) of this abstract have provided an email address for comments about the abstract: lmt@astro.as.utexas.edu
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.