Asteroid Polarimetric-Phase Behavior in the Near-Infrared: S- and C-Complex Objects

TL;DR

This study presents near-infrared polarization-phase curves of asteroids, confirming the instrument's precision and revealing wavelength-dependent behaviors that can inform surface composition analysis.

Contribution

First near-infrared polarization-phase curves for asteroids using WIRC+Pol, demonstrating calibration potential with C-complex asteroids and extending understanding of surface properties.

Findings

WIRC+Pol achieves 0.1% polarization measurement precision.

C-complex asteroids show less wavelength variation, useful for calibration.

S-complex asteroids exhibit a shift in polarization behavior from visible to near-infrared.

Abstract

We present the first results of our survey of asteroid polarization-phase curves in the near-infrared J and H bands using the WIRC+Pol instrument on the Palomar 200-inch telescope. We confirm through observations of standard stars that WIRC+Pol can reach the 0.1% precision needed for asteroid phase curve characterization, and show that C-complex asteroids could act as an alternate calibration source as they show less wavelength variation than stellar polarized standards. Initial polarization-phase curve results for S-complex asteroids show a shift in behavior as a function of wavelength from visible to near-infrared bands, extending previously observed trends. Full near-infrared polarization-phase curve characterization of individual asteroids will provide a unique constraint on surface composition of these objects by probing the wavelength dependence of albedo and index of refraction of the surface material.