Material Around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation

TL;DR

This paper reports the detection of material around Centaur Chiron from a 2018 stellar occultation, indicating evolving ring properties and ruling out a global atmosphere at tens of microbars.

Contribution

First detection of surrounding material around Chiron from 2018 occultation, supporting a multi-ring system with evolving properties compared to previous observations.

Findings

Detected multiple ring-like features around Chiron.

No global atmosphere detected at tens of microbars.

Ring properties have changed since 2011 observations.

Abstract

A stellar occultation of Gaia DR3 2646598228351156352 by the Centaur (2060) Chiron was observed from the South African Astronomical Observatory on 2018 November 28 UT. Here we present a positive detection of material surrounding Chiron from the 74-in telescope for this event. Additionally, a global atmosphere is ruled out at the tens of mircobar level for several possible atmospheric compositions. There are multiple 3-sigma drops in the 74-in light curve: three during immersion and two during emersion. Occulting material is located between 242-270 km from the center of the nucleus in the sky plane. Assuming the ring-plane orientation proposed for Chiron from the 2011 occultation, the flux drops are located at 352, 344, and 316 km (immersion), and 357, and 364 km (emersion) from the center, with normal optical depths of 0.26, 0.36, and 0.22 (immersion) and 0.26 and 0.18 (emersion), and equivalent widths between 0.7-1.3 km. This detection is similar to the previously proposed two-ring system and is located within the error bars of that ring-pole plane; however, the normal optical depths are less than half of the previous values, and three features are detected on immersion. These results suggest that the properties of the surrounding material have evolved between the 2011, 2018, and 2022 observations.