New determination of the size and bulk density of the binary asteroid 22 Kalliope from observations of mutual eclipses

TL;DR

This study used mutual eclipse observations of binary asteroid 22 Kalliope to refine its size, shape, and density, providing more accurate physical parameters and insights into its composition.

Contribution

It presents a new model incorporating a refined shape of Kalliope and eclipse data to accurately determine its size and density, improving previous estimates.

Findings

Kalliope's diameter is estimated at 166.2 km, 8% smaller than previous IRAS measurements.

The bulk density of Kalliope is calculated as 3.35 g/cm³, higher than earlier estimates.

Linus's diameter is estimated at 28 km, assuming a spherical shape.

Abstract

In 2007, the M-type binary asteroid 22 Kalliope reached one of its annual equinoxes. As a consequence, the orbit plane of its small moon, Linus, was aligned closely to the Sun's line of sight, giving rise to a mutual eclipse season. A dedicated international campaign of photometric observations, based on amateur-professional collaboration, was organized and coordinated by the IMCCE in order to catch several of these events. The set of the compiled observations is released in this work. We developed a relevant model of these events, including a topographic shape model of Kalliope refined in the present work, the orbit solution of Linus as well as the photometric effect of the shadow of one component falling on the other. By fitting this model to the only two full recorded events, we derived a new estimation of the equivalent diameter of Kalliope of 166.2+/-2.8km, 8% smaller than its IRAS diameter. As to the diameter of Linus, considered as purely spherical, it is estimated to 28+/-2 km. This substantial "shortening" of Kalliope gives a bulk density of 3.35+/-0.33g/cm3, significantly higher than past determinations but more consistent with its taxonomic type. Some constraints can be inferred on the composition.