A CCD search for Lagrangian asteroids of the Earth-Sun system

The L4 and L5 points of the Earth-Sun system were imaged using the Universi ty of Hawaii 2.24-m telescope on 1994 May 5-7 and July 6-8 UT. We used a th inned Tektronix 2048 x 2048 CCD, subtending a field 7.5 arcmin on a side. O ur objective in this search was to locate sub-kilometer-sized asteroids orb iting near the libration point or, failing this, to set a rough upper limit on the number density of objects contained in such a population. Previous searches of these areas have used various less sensitive photographic techn iques, but no asteroids have ever been discovered at the L4 or L5 points of the Earth-Sun system. The limiting sensitivity of this search was R simila r to 22.8, corresponding to C-type asteroids similar to 350 m in diameter o r S-type asteroids similar to 175 m in diameter. No objects were discovered in the approximately 0.35 square degrees covered, leading to our crude est imate that the upper limit for the number density of objects at or above ou r detection threshold is approximately 3 objects per square degree. In this paper, we discuss the various considerations governing our search strategy . We also discuss the relevence of this search technique in looking for nea r-Earth asteroids in general. Finally, in this paper we point out areas of future theoretical work that can yield important information on Earth's lib ration regions, and we discuss the outlook for using large mosaic arrays in future asteroid searches of this nature. (C) 1998 Academic Press.