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Keck and VLT AO observations and models of the uranian rings during the 2007 ring plane crossings

de Pater, Imke and Dunn, David E. and Stam, Daphne M. and Showalter, Mark R. and Hammel, Heidi B. and Min, Michiel and Hartung, Markus and Gibbard, Seran G. and van Dam, Marcos A. and Matthews, Keith (2013) Keck and VLT AO observations and models of the uranian rings during the 2007 ring plane crossings. Icarus, 226 (2). pp. 1399-1424. ISSN 0019-1035.

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We present observations of the uranian ring system at a wavelength of 2.2 μm, taken between 2003 and 2008 with NIRC2 on the W.M. Keck telescope in Hawaii, and on 15–17 August 2007 with NaCo on the Very Large Telescope (VLT) in Chile. Of particular interest are the data taken around the time of the uranian ring plane crossing with Earth on 16 August 2007, and with the Sun (equinox) on 7 December 2007. We model the data at the different viewing aspects with a Monte Carlo model to determine: (1) the normal optical depth τ_0, the location, and the radial extent of the main rings, and (2) the parameter Aτ_0 (A is the particle geometric albedo), the location, and the radial plus vertical extent of the dusty rings. Our main conclusions are: (i) The brightness of the ∊ ring is significantly enhanced at small phase and ring inclination angles; we suggest this extreme opposition effect to probably be dominated by a reduction in interparticle shadowing. (ii) A broad sheet of dust particles extends inwards from the λ ring almost to the planet itself. This dust sheet has a vertical extent of ∼140 km, and Aτ_0 = 2.2 × 10^(−6). (iii) The dusty rings between ring 4 and the α ring and between the α and β rings are vertically extended with a thickness of ∼300 km. (iv) The ζ ring extends from ∼41,350 km almost all the way inwards to the planet. The main ζ ring, centered at ∼39,500 km from the planet, is characterized by Aτ_0 = 3.7 × 10^(−6); this parameter decreases closer to the planet. The ζ ring has a full vertical extent of order 800–900 km, with a pronounced density enhancement in the mid-plane. (v) The η_c ring is optically thin and less than several tens of km in the vertical direction. This ring may be composed of macroscopic material, surrounded by clumps of dust.

Item Type:Article
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URLURL TypeDescription
de Pater, Imke0000-0002-4278-3168
Hammel, Heidi B.0000-0001-8751-3463
Additional Information:© 2013 Elsevier Inc. Received 26 October 2012. Revised 18 July 2013. Accepted 1 August 2013. Available online 14 August 2013. We thank Larry Sromovsky and Patrick Fry for contributing data to our program on UT 19 and 20 August, 2007, and Daniel Guirado Rodríguez for insightful discussions with regard to the opposition effect. We thank the referees for their help to significantly improve our manuscript. Most of the near-infrared data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. This work was further supported in part by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement AST 98-76783. In addition, IdP acknowledges support from NASA Grant NNX07AK70G, and MRS was supported by NASA’s Planetary Geology and Geophysics program through Grant NNX09AG14G. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
NSF Science and Technology Center for Adaptive OpticsAST 98-76783
NASA Planetary Geology and Geophysics programNNX09AG14G
Subject Keywords: Planetary rings; Uranus; Infrared observations
Issue or Number:2
Record Number:CaltechAUTHORS:20131121-140446050
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Official Citation:Imke de Pater, David E. Dunn, Daphne M. Stam, Mark R. Showalter, Heidi B. Hammel, Michiel Min, Markus Hartung, Seran G. Gibbard, Marcos A. van Dam, Keith Matthews, Keck and VLT AO observations and models of the uranian rings during the 2007 ring plane crossings, Icarus, Volume 226, Issue 2, November–December 2013, Pages 1399-1424, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42628
Deposited By: Ruth Sustaita
Deposited On:21 Nov 2013 22:33
Last Modified:09 Mar 2020 13:19

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