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[43.08] HST and IRTF Observations of Neptune during 1998

L. A. Sromovsky, P. M. Fry, S. S. Limaye (Univ. of Wisconsin), K. H. Baines (Jet Propulsion Laboratory), T. Dowling (Univ. of Louisville)

Neptune's dynamic weather system produces discrete cloud features and zonal bands, covering a wide range of temporal and spatial scales. To better understand the vertical distribution and microphysical properties of these various cloud forms, as well as their drift rates and evolutionary properties, an intensive program of observations was devised for June and August of 1998, with the secondary objective of measuring Triton's light curve and current spectral properties to serve both as a photometric reference for Neptune observations and to track expected changes in the relative amounts of various surface ice components as Triton's northern hemisphere approaches summer solstice around 2000 AD. The first set of observations were carried out at the IRTF during 12-15 June with NSFCAM at near-IR wavelengths, using broad-band J, H, 1.7 micron (Spencer H), K filters, CVF filters at 1.59, 2.0, 2.07, and 2.1 microns, and IJH and HKL grisms. Images show prominent bright cloud features, one near 30 N, possibly associated with the dark spot discovered in 1994 (Hammel et al., {\it Science, \bf 268}, 1994), and two near 50 S, separated by about 180 degrees of longitude, a pattern similar to that seen in 1996 observations (Sromovsky et al., {\it BAAS,\bf 28}, 1996). Spectra for individual cloud features show CH₄ and H₂ CIA absorption signatures that will be used to constrain cloud top altitudes. Triton's spectrum contains prominent ice signatures similar to those seen by Cruikshank et al. ({\it Science,\bf 261}, 1993), but quantitative comparisons await further analysis. HST observations using WFPC2 and NICMOS are planned for 11-12 August 1998, using 9 orbits to cover two rotations of Neptune. The HST observations take place in the middle of a 10-13 August (UT) IRTF observing run using NSFCAM. We will present preliminary results of these coordinated observations.