# # Program information file # PROGRAM_ID 2022B048 PROGRAM_TITLE Stellar occultations by the large trans-Neptunian objects Quaoar and 55638 PROGRAM_INV1 Amanda Sickafoose PROGRAM_INV2 Carlos Zuluaga PROGRAM_INV3 Michael Person PROGRAM_INV4 Amanda Bosh PROGRAM_INV5 Stephen Levine PROGRAM_SCICAT Centaurs / TNOs / KBOs PROGRAM_ABSTRACT_BEG Stellar occultations are one of the most accurate ground-based methods to measure sizes, shapes, and atmospheres 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 Trans-Neptunian Objects [TNOs]. We propose for 7.5 hours to observe three predicted stellar occultations by the large TNOs [50000] Quaoar [3.5 hours] and 55638 [4 hours]. Recent occultation observations of Quaoar have revealed surrounding material: a successful observation could confirm those findings and provide additional insight into possible activity processes. A positive detection by 55638 would place a tighter constraints on size, potential atmosphere, and any material around the body. The UT mid-times for the predicted events are on 09 August [Quaoar] and 14 October [55638]. We typically request 4 hours for each of the events, here the 09 August observation is constrained slightly by twilight. We observe at high cadence for +/-20 min centered on each predicted midtime. When possible, long-exposure, calibration frames are taken 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. SpeX will be employed to obtain simultaneous K-band image for all the 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