  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.
