Size Distribution of Faint Jovian L4 Trojan Asteroids

Abstract

We detected 51 faint Jovian Trojan asteroids in the L4 Lagrangian swarm in survey observations near opposition and the ecliptic using a wide-field mosaicked CCD camera on the 8.2 m Subaru Telescope. We report the Trojan size distributions in this paper. The surveyed sky area was about 3 deg2 and located ~30° in longitude ahead of the L4 point. From trailed-image simulations of hypothetical Trojans, we measured the 90% complete detection limiting magnitudes for our Trojan asteroids on a CCD chip-by-chip basis. The limiting magnitudes varied by 0.4–0.5 mag between chips; therefore, we introduce a new measure of detection limit appropriate for multichip CCD cameras. By statistically comparing the observed number of Trojans with the predictions from theoretical size distributions near the limiting magnitude calculated in this way, we determined a limiting diameter of D ~ 2 km, corresponding to the detection limit of this survey. On the other hand, the detected Trojans covered a size range of 0.7 km 1 km. Finally, we discuss, from a cosmogonic viewpoint, a possible relation between Trojans and short-period comets on the basis of their size distribution slopes.