The multiwavelength phase curves of small bodies

Phase coloring^★

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

Received: 16 October 2023
Accepted: 16 February 2024

Abstract

Context. Small bodies change their brightness for different reasons: rotation along their axis or axes, combined with irregular shapes and/or changing surface properties, or changes in the observation geometry. We investigate the problem of phase curves, which show the change in brightness due to changes in the fraction of illuminated surface as seen by the observer.

Aims. We study the effect of the phase curves in the five wavelengths of the Sloan Digital Sky Survey in scores of objects (several tens of thousands). We focus in particular on the spectral slopes and the colors and their changes with phase angle.

Methods. We used a Bayesian inference method and Monte Carlo techniques to retrieve the absolute magnitudes in five wavelengths. We used the results to study the phase-coloring effect in different bins of the semimajor axis.

Results. We obtained absolute magnitudes in the five filters for over 40 000 objects. Although some outliers are identified, most of the usual color–color space is recovered by the data we presented. We also detect a dual behavior in the spectral slopes, with a change at a ~ 5 deg.