# # Program information file # PROGRAM_ID 2024B027 PROGRAM_TITLE Stellar occultations by the trans-Neptunian object Quaoar and the Centaur Chiron PROGRAM_INV1 Amanda Sickafoose PROGRAM_INV2 Carlos Zuluaga PROGRAM_INV3 Michael Person PROGRAM_INV4 Stephen Levine PROGRAM_INV5 PROGRAM_SCICAT Centaurs / TNOs / KBOs PROGRAM_ABSTRACT_BEG Stellar occultations are one of the most accurate ground-based methods to measure sizes, shapes, atmospheres, and rings of distant bodies in the Solar System. The capabilities of MORIS+SpeX, combined with Hawaii's unique geographic location, have proven successful for observing stellar occultations by such objects. We propose for 8 hours to observe two predicted stellar occultations, one each by the large TNO [50000] Quaoar and the Centaur [2060] Chiron. A system of two inhomogeneous rings has recently been proposed around Quaoar, detected by only a handful of observations. Even more recent stellar occultations by Chiron indicate that the previously-proposed two-ring system is instead surrounding material that is evolving. Successful observations would characterize the locations and optical depths of rings/surrounding material in the current epoch, detect changes since the last observed occultations, and provide insight into possible activity processes The UT mid-times for the predicted Quaoar and Chiron events are on August 11 and September 17, respectively. We request 4 hours for each event, to observe [i] at high cadence for +/-20 min centered on the predicted and [ii] long-exposure, calibration frames before and after, when the star and object are well separated. MORIS will be run with no filter at the fastest cadence that allows for a light-curve signal-to-noise of at least a few tens: for these targets, the resulting integration times are 0.06 sec and 1 sec for the respective events. SpeX will be employed to obtain simultaneous K-band image for both events. Visible data are used to constrain object sizes and atmospheres, as well as the extent and structure of surrounding material. Multi-color data provide an additional level of characterization, through providing insight into [i] particle sizes in atmospheric haze or surrounding material and [ii] nucleus shapes, through central-flash modeling. PROGRAM_ABSTRACT_END