Near-infrared adaptive optics imaging of the satellites and individual rings of Uranus

Abstract

We present the first Earth-based images of several of the individual faint rings of Uranus, as observed with the adaptive optics system on the W.M. Keck II telescope on four consecutive days in October 2003. We derive reflectivities based on multiple measurements of 8 minor moons of Uranus as well as Ariel and Miranda in filters centered at wavelengths of 1.25(J), 1.63(H), and 2.1(Kp) µm. These observations have a phase angle of 1.84 • -1.96 • . We find that the small satellites are somewhat less bright than in observations made by the HST at smaller phase angles, confirming an opposition surge effect. We calculate albedoes for the ring groups and for each ring separately. We find that the ring particles, as well as the particles in the three other ring groups, have albedoes near 0.043 at these phase angles. The equivalent depths of some of the individual rings are different than predicted based upon ring widths from occultation measurements (assuming a constant particle ring brightness); in particular the γ ring is fainter and the η ring brighter than expected. Our results indicate that q, the ratio of ring intensity at apoapse vs. periapse, is close to 3.2 ± 0.16. This agrees well with a model that has a filling factor for the ring of 0.06 (Karkoschka, 2001, Icarus 151, 78-83). We also determine values of the north to south brightness ratio for the individual rings and find that in most cases they are close to unity.

Two new, rare, high-effusion outburst eruptions at Rarog and Heno Paterae on Io

“…1 and 2). Because only a fraction of the total radiant flux is contained in the eruption as we see it (i.e., in the central part of the PSF), we corrected the radiant fluxes for the fraction that is lost in the halo of the PSF, as described by Gibbard et al (2005) and. The errors in the radiant fluxes are based on the photometric uncertainty and the variation in radiant flux as derived by using different apertures to determine the flux.…”

Long-term atmospheric variability on Uranus and Neptune

“…Lockwood and Thompson, 1999). Other lines show synthetic light curves with non-polar brightness levels that are increas- Gibbard et al, 2005) were obtained on October 5 (upper) and October 6 (lower) with the NIRC2 camera at J , H , and K filters (1.2, 1.6, and 2.2 µm, respectively). There is no sign of a northern polar cap of comparable brightness to that seen in the south.…”

“…Extensive activity is seen across the planetary disk, even in near-equatorial latitudes. Uranian rings (discussed in Gibbard et al, 2005), dominate at K ; the epsilon ring can be discerned as a thin faint line across the planetary disk in the H and J images. (b) These Neptune images (adapted from de Pater et al, 2005) are one-minute H -band exposures taken on July 28 (left) and October 3 (right).…”

Near-infrared monitoring of Io and detection of a violent outburst on 29 August 2013

“…We then correct for flux lost to the wings of the point-spread function (PSF) by applying the same aperture and background radius to stellar observations and determining the fraction of total flux recovered, following the procedure of Gibbard et al (2005). We observe a standard star only every $10 nights of observation for PSF estimation.…”