Abstract
Abstract We report the first measurement of the zodiacal light (ZL) polarization spectrum in the near-infrared between 0.8 and 1.8 μm. Using the low-resolution spectrometer on board the Cosmic Infrared Background Experiment, calibrated for absolute spectrophotometry and spectropolarimetry, we acquire long-slit polarization spectral images of the total diffuse sky brightness toward five fields. To extract the ZL spectrum, we subtract the contribution of other diffuse radiation, such as the diffuse galactic light, the integrated starlight, and the extragalactic background light. The measured ZL polarization spectrum shows little wavelength dependence in the near-infrared, and the degree of polarization clearly varies as a function of the ecliptic coordinates and solar elongation. Among the observed fields, the North Ecliptic Pole shows the maximum degree of polarization of ∼20%, which is consistent with an earlier observation from the Diffuse Infrared Background Experiment on board on the Cosmic Background Explorer. The measured degree of polarization and its solar elongation dependence are reproduced by an empirical scattering model in the visible band and also by a Mie scattering model for large absorptive particles, while a Rayleigh scattering model is ruled out. All of our results suggest that the interplanetary dust is dominated by large particles.
Highlights
Zodiacal light (ZL) arises from sunlight scattered by the interplanetary dust (IPD) in the optical and the near-infrared (3 μm)
We show the ZL polarization spectrum, PZL(λ), of the five fields measured in the third flight in Figure 11 and Table 3
We provide another test for the IPD size by comparing the ZL polarization spectrum with the polarization of Mie scattering theories
Summary
Zodiacal light (ZL) arises from sunlight scattered by the interplanetary dust (IPD) in the optical and the near-infrared (3 μm). In the near-infrared, only Berriman et al (1994) have measured the polarization of the ZL from space by the Diffuse Infrared Background Experiment (DIRBE) on board on the Cosmic Background Explorer (COBE) in discrete photometric bands at 1.25, 2.2, and 3.5 μm This result shows that the degree of polarization of the ZL is about 10% ∼ 20% at solar elongation ò = 90° , and tends to decrease toward longer wavelengths. CIBER, designed to study the diffuse near-infrared emission above the Earth’s atmosphere (Zemcov et al 2013), housed three instruments including two broadband imagers (Bock et al 2013), a narrowband spectrometer (Korngut et al 2013), as well as the LRS, designed to measure the spectrum of diffuse light in 0.8 λ 1.8 μm (Tsumura et al 2013) with a wavelength resolution of λ/Δλ = 15–30. As the solar elongation increases, the polarization is expected to decrease
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