Title: Observations of Rosetta Target (21) Lutetia with Keck and Gemini
Adaptive Optics

Al Conrad (Keck)

Abstract: 

In support of the NASA/ESA Rosetta mission~s plans to observe asteroid
(21) Lutetia during a 2010 July flyby, and in conjunction with a
larger ground-based plus HST campaign to support this mission, we
observed Lutetia from Keck and Gemini-North during several nights
spanning 2008 Oct through 2009 Jan. Observations were made using
adaptive optics in the near-IR, primarily at K-band (2.1 micron), and
were timed to coincide with the asteroid's most recent opposition at a
distance of about 1.4 AU. From these data, we determined Lutetia~s
triaxial size and shape to be 132 x 101 x 76 km, with maximum expected
uncertainties of 4 x 3 x 31 km. The spin pole is found to be at (RA,
Dec) = (48, +9) deg or ecliptic (long, lat) = (49,-8) deg, with a
formal uncertainty radius (not including systematics) of 3 deg. We
have calibrated our technique of deriving dimensions of asteroids from
AO images against Pluto and 4 satellites of Saturn with accurate
diameters, and we expect that our systematics (included in the size
uncertainties above) are no more than 3%.
 
We also searched for satellites and our preliminary results indicate
no detection of a satellite larger than about 1 km over a significant
fraction of the Hill sphere (10-240 asteroid radii). Improved limits
are expected from a more refined analysis.