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[24.02] Near-infrared Imaging of Large Main-belt Asteroids with the Keck Adaptive Optics System

A. Conrad, D. Le Mignant (W. M. Keck Observatory), C. Dumas (Jet Propulsion Laboratory, Caltech), W. J. Merline (Southwest Research Institute), H.B. Hammel (Space Science Institute), T. Fusco (Onera, France), R. Campbell, F. Chaffee, R. Goodrich, S. Kwok (W. M. Keck Observatory)

We present recent high-angular-resolution imaging results obtained on main-belt asteroids with the Keck II telescope Adaptive Optics (AO) system and its near-infrared camera NIRC2. With H band spatial resolution ranging from 30 km (inner main-belt) to 60 km (outer main-belt), the Keck AO system is a powerful instrument for making the first, detailed, ground-based geological study of the large asteroids (i.e., those asteroids with angular size > 0.15 arcsec). AO on large telescopes can be used to investigate the distribution of albedo across the asteroid's surface and directly measure the asteroid's shape, its spin sense (prograde/retrograde), and the direction of its spin axis. The combination of AO and large aperture provides an efficient configuration to study and explore the potential targets of future space missions to asteroids.

Asteroid 511 Davida (mean physical diameter of 320 km) was imaged over a full rotation period (5.13 h) during its last opposition of December 2002. Its angular diameter was 0.28 arcsec and the asteroid was seen nearly pole-on. The 40 milliarcsec angular resolution of the Keck II telescope at H band corresponded to a resolution of approximately 46 km at the geocentric distance of Davida, with approximately 7 resolution elements across the diameter (28 pixels in this imaging mode), corresponding to 38 resolution elements covering the visible disk (616 pixels). No surface albedo features could be detected at this wavelength. We report its physical dimension and we estimate the direction of its rotation axis. Additional imaging results obtained on asteroids 3 Juno, 7 Iris, 12 Victoria and 45 Eugenia are also presented. Unlike Davida, objects 3 Juno and 7 Iris display albedo variations across the surface.

The author(s) of this abstract have provided an email address for comments about the abstract: aconrad@keck.hawaii.edu

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.