Absolute colors and phase coefficients of asteroids^★

¹ Instituto de Astrofísica de Andalucía, CSIC, Apt 3004, 18080 Granada, Spain
e-mail: varobes@gmail.com
² Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante, San Vicent del Raspeig, 03080 Alicante, Spain
³ Observatório Nacional/MCTIC, Rua General José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
⁴ Universidad Internacional de Valencia, Valencia, Spain
⁵ Instituto de Astronomía Teórica y Experimental, CONICET-UNC, Laprida 854, Córdoba, Argentina

Received: 4 March 2022
Accepted: 21 September 2022

Abstract

Context. We use the phase curves of small bodies to measure absolute magnitudes and, together with complementary theoretical and laboratory results, to understand the micro- and macroscopic properties of their surfaces. 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 7−10 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 to directly compare data taken for objects in the inner Solar System (inside the orbit of Jupiter) with data for centaurs and trans-Neptunian objects.

Methods. We use the SLOAN Moving Objects Catalog (MOC) data to construct phase curves restricted to phase angles of less than or equal to 7.5 deg, which is compatible with the angles observed for the trans-Neptunian and 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 obtain absolute magnitudes in seven filters for over 4000 objects. Our comparison with outer Solar System objects suggests the surfaces have a common property: intrinsically redder objects become blue with increasing phase angle, while the opposite happens for intrinsically bluer objects.