# # Program information file # PROGRAM_ID 2022A020 PROGRAM_TITLE Stellar occultations by Pluto and Quaoar PROGRAM_INV1 Amanda Sickafoose PROGRAM_INV2 Michael Person PROGRAM_INV3 Carlos Zuluaga 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 12 hours to observe three predicted stellar occultations by the dwarf planet Pluto and the large TNO Quaoar. Pluto's atmosphere has been evolving and some thermophysical models suggest that it should undergo a rapid pressure decline in the next decades. A successful occultation observation will return Pluto's atmospheric characteristics in the current epoch. Recent occultation observations of Quaoar have revealed surrounding material: a successful observation could confirm those findings and provide additional insight into activity processes on small bodies. The UT mid-times for the predicted events are on 17 April [Pluto] and 07 and 11 June [Quaoar]. We request 4 hours for each of the events. 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 between 0.06 and 5 sec. SpeX will be employed to obtain simultaneous K-band image for the events that have sufficiently bright stars [11 June]. 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