The asteroid distribution in the ecliptic

Abstract

We present analysis of the asteroid surface density distribution of main-belt asteroids (mean perihelion Δ ≃ 2.404 AU) in five ecliptic latitude fields, -17 ≳ β(°) ≲ +15, derived from deep Large Binocular Telescope V-band (85% completeness limit V = 21.3 mag) and Spitzer Space Telescope IRAC 8.0 μm (80% completeness limit ∼103 μJy) fields enabling us to probe the 0.5-1.0 km diameter asteroid population. We discovered 58 new asteroids in the optical survey as well as 41 new bodies in the Spitzer fields. The derived power-law slopes of the number of asteroids per square degree are similar within each ∼5° ecliptic latitude bin with a mean value of -0.111 ± 0.077. For the 23 known asteroids detected in all four IRAC channels mean albedos range from 0.24 ± 0.07 to 0.10 ± 0.05. No low-albedo asteroids (pV ≲ 0.1) were detected in the Spitzer FLS fields, whereas in the SWIRE fields they are frequent. The SWIRE data clearly samples asteroids in the middle and outer belts providing the first estimates of these km-sized asteroids' albedos. Our observed asteroid number densities at optical wavelengths are generally consistent with those derived from the Standard Asteroid Model within the ecliptic plane. However, we find an overdensity at β ≳ 5° in our optical fields, while the infrared number densities are underdense by factors of 2 to 3 at all ecliptic latitudes. © 2009. The American Astronomical Society. All rights reserved.