# # Program information file # PROGRAM_ID 2021B023 PROGRAM_TITLE The best stellar occultation by Neptune in decades PROGRAM_INV1 Amanda Sickafoose PROGRAM_INV2 Damya Souami PROGRAM_INV3 Josselin Desmars PROGRAM_INV4 Stefan Renner PROGRAM_INV5 Bruno Sicardy PROGRAM_SCICAT solar system PROGRAM_ABSTRACT_BEG We propose to study the properties of Neptune's atmosphere and ring system by means of stellar occultation. The complete study of the Neptunian system dates back to Voyager in 1989. Stellar occultations from 1983-1990 have allowed discovery of the arcs [incomplete ring-like structures] and a probe of the upper atmosphere of Neptune. An occultation on 07 October 2021 is the first opportunity in over 30 years to measure the optical depth of the rings and constrain further the material's redistribution. Furthermore, it will allow us to probe the upper atmosphere of Neptune searching for seasonal changes in the temperature profiles. The the predicted time for the Neptune system to occult the star is from approximately 06:00 to 08:00 UT on 07 October 2021. We request 4 hours to observe the event, from 04:30-08:30 UT. During the two-hour occultation, SpeX Guidedog will be used to take K-band images at the fastest cadence that allows for a light-curve signal-to-noise of at least a few tens. MORIS will be be employed to obtain simultaneous data in the SDSSz filter, also at the fastest cadence that allows for a light-curve signal-to-noise of at least a few tens. We will test different exposure times for both instruments before the event, to optimize light curve SNR [Neptune's brightness and conditions on that night being taken into consideration0. Longer-exposure, calibration frames will be taken before and after, when the star and Neptune are better separated. These data will be used to create light curves, from which ring and ring-arc optical depths will be derived as well as Neptune's atmospheric properties. PROGRAM_ABSTRACT_END