Results of two multi-chord stellar occultations by dwarf planet (1) Ceres

TL;DR

This study reports two stellar occultation observations of Ceres, deriving its size and shape with elliptical models, and compares these results with previous measurements, providing valuable data ahead of NASA's Dawn mission.

Contribution

First to analyze multiple occultations of Ceres to determine its size and shape using elliptical models and pole constraints.

Findings

Estimated equatorial diameter of 972 ± 6 km.

Apparent oblateness of 0.08 ± 0.03.

Results consistent with prior size determinations.

Abstract

We report the results of two multi-chord stellar occultations by the dwarf planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the USA on 2013 October 25. Four positive detections were obtained for the 2010 occultation, and nine for the 2013 occultation. Elliptical models were adjusted to the observed chords to obtain Ceres' size and shape. Two limb fitting solutions were studied for each event. The first one is a nominal solution with an indeterminate polar aspect angle. The second one was constrained by the pole coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we determine an equatorial diameter of 972 $\pm$ 6 km and an apparent oblateness of 0.08 $\pm$ 0.03 as our best solution. These results are compared to all available size and shape determinations for Ceres made so far, and shall be confirmed by the NASA's Dawn space mission.