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P. M. Fry, L. A. Sromovsky (University of Wisconsin - Madison)
On August 11 2004 we imaged the Uranus (0.8 deg. phase) and Neptune (0.2 deg. phase) systems in the near-infrared with the Keck 2 NIRC2 camera using adaptive optics. We determined broadband J and H albedos for Uranus (1.58E-2, 1.01E-2 respectively, values preliminary), and J, H, and Kp albedos for Triton (0.77, 0.67, 0.59 respectively). Uncertainties are estimated to be 5-10%. We determined narrowband satellite albedos as follows:
| Central Wavelength | Ariel | Umbriel | Miranda | Oberon | Triton | |
| Hcont | 1.5804 | 0.303 | 0.179 | 0.254 | 0.216 | 0.747 |
| FeII | 1.6455 | 0.297 | 0.179 | 0.241 | 0.216 | 0.633 |
| He1B | 2.0563 | 0.199 | 0.153 | 0.182 | 0.168 | 0.653 |
| NB2.108 | 2.1281 | 0.280 | 0.182 | 0.251 | 0.210 | 0.610 |
These data augment those of Karkoschka (Icarus 151, 51-68, 2001), where values for Umbriel and Oberon were not available.
Photometric reductions include infinite aperture corrections using both AO and non-AO growth curve characterizations. A significant fraction of the total energy can extend out to a radius of 3-5 arcseconds. This has implications for disk-integrated photometry and discrete feature I/F measurements.
Miranda and Ariel results are in good agreement with the HST results of Karkoschka (2001). Our photometry also compares well to the UKIRT Miranda photometry and spectrum of Bauer et al. (Icarus 158, 178-190, 2002) and our IRTF photometry of Triton in 1996 (Sromovsky et al., Icarus 149, 435-458, 2001). Miranda and Ariel albedos from Gibbard et al. (Icarus 174, 253-262, 2005), from Keck, are significantly lower than ours, and those of Baines et al. (Icarus 132, 266-284, 1998, IRTF) differ sporadically.
Determination of full-disk albedos of Uranus is a work in progress. Difficulties include incomplete brightness integreation due to the restrictive narrow camera FOV, and subtraction of the ring system brightness contribution, especially at wavelengths where methane and hydrogen absorption are significant.
This work is supported by a grant from the NASA Planetary Astronomy Program.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.