Keck NIRC2 photometry of Uranus, uranian satellites, and Triton in August 2004

Abstract

On August 11, 2004, we made adaptive optics observations of the Uranus and Neptune systems with the Keck II Near Infrared Camera. Uranus and Triton were observed in three broadband filters (J, H, and K-prime) and four narrowband filters [Hcont, FeII, He1_B, and H 2 ( v = 1 - 0 ) ]. Miranda, Ariel, Umbriel, and Oberon were observed in the four narrowband filters only. To achieve the highest possible photometric accuracy, and thus the tightest possible constraints on atmospheric aerosol models and gas mixing ratios, we used aperture photometry that accounted for the dependence of point-spread functions and growth curves on the adaptive optics reference object, and accounted for recently determined phase curves of each object. The satellite albedos we determined were compared with published relative spectra to verify the relative consistency of our observations, which were subsequently used to convert published relative spectra to absolute spectra. We used these absolute spectra and synthetic photometry methods to compare published values in dissimilar photometric systems to each other and to our observations. We find our satellite albedos in best agreement with photometry from Karkoschka [Karkoschka, E., 2001. Icarus 151, 51–68], which is the best characterized and most contemporaneous data set. Our estimated absolute accuracy of 5% to 8% is consistent with these intercomparisons. We obtained the following ring-subtracted and discrete feature-free albedos of Uranus: J: ( 1.66 ± 0.07 ) × 10 −2 , H: ( 1.09 ± 0.05 ) × 10 −2 , K ′ : ( 2.08 ± 0.15 ) × 10 −4 , Hcont: ( 3.71 ± 0.23 ) × 10 −2 , FeII: ( 1.14 ± 0.07 ) × 10 −3 , He1_B: ( 2.06 ± 0.16 ) × 10 −4 , and H2: ( 1.27 ± 0.10 ) × 10 −4 .