Absolute colors and phase coefficients of asteroids

TL;DR

This study analyzes phase curves of over 4000 small bodies to determine their absolute magnitudes and phase coefficients across multiple filters, revealing surface color trends related to phase angle in inner and outer solar system objects.

Contribution

It provides a comprehensive comparison of phase curve data for inner solar system asteroids and outer solar system objects, using a linear model to derive surface properties.

Findings

Redder objects tend to become bluer with increasing phase angle.

Bluer objects tend to become redder with increasing phase angle.

Surface color changes are consistent across a large sample of small bodies.

Abstract

Context: We use phase curves of small bodies to measure absolute magnitudes and, together with complementary theoretical and laboratory results, to understand their surfaces' micro and macroscopic properties. Although we can observe asteroids up to phase angles of about 30 deg, the range of phase angles covered by outer solar system objects usually does not go further than 7 to 10 deg for centaurs and 2 deg for trans-Neptunian objects, and a linear relation between magnitude and phase angle may be assumed. Aims: We aim at directly comparing data taken for objects in the inner solar system (inside the orbit of Jupiter) with data of centaurs and trans-Neptunian objects. Methods: We use the SLOAN Moving Objects Catalog data to construct phase curves restricted to phase angles less than or equal to 7.5 deg, compatible with the angles observed for the trans-Neptunian/Centaur population. We assume a linear model for the photometric behavior to obtain absolute magnitudes and phase coefficients in the ugirz, V, and R filters. Results: We obtained absolute magnitudes in seven filters for $>4000$ objects. Our comparison with outer solar system objects points to a common property of the surfaces: intrinsically redder objects become blue with increasing phase angle, while the opposite happens for intrinsically bluer objects.