Near-infrared Polarization Charateristics of the Zodiacal Light Observed with DIRBE/COBE

Abstract

We report near-infrared polarization of the zodiacal light (ZL) measured from space by the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer in photometric bands centered at 1.25, 2.2, and 3.5 μ m. To constrain the physical properties of interplanetary dust, we use DIRBE Weekly Sky Maps to investigate the solar elongation ( ϵ ), ecliptic latitude ( β ), and wavelength ( λ ) dependence of ZL polarization. We find that the polarization of the ZL varies as a function of ϵ and β , consistent with observed polarization at λ = 550 nm. While the polarization dependence on wavelength at ( ϵ , β ) = (90°, 0°) is modest (increasing from 17.7% ± 0.2% at 1.25% μ m to 21.0% ± 0.3% at 3.5 μ m), the variation is more pronounced at the north ecliptic pole (23.1% ± 1.6%, 35.1% ± 2.0%, and 39.3% ± 2.1% at 1.25, 2.2, and 3.5 μ m, respectively). The variation in ZL polarization with wavelength is not explained by either Rayleigh scattering or absorptive particles larger than 10 μ m.

Keywords

• Interplanetary dust
• Zodiacal cloud
• Infrared Astronomical Satellite
• Polarimetry
• Near infrared astronomy