Stellar Occultation Predictions: A Case Study of the 1997 July 18 Triton Occultation

C. B. Olkin (Lowell Observatory), J. L. Elliot (MIT/Lowell Observatory), E. W. Dunham (Lowell Observatory), S. W. McDonald, M. A. Agner (MIT), A. S. Bosh (Lowell Observatory), M. J. Person (MIT), A. White (Lowell Observatory)

Stellar occultations can provide high-spatial resolution information about a planetary atmosphere such as temperature and pressure profiles, optical depth, and oblateness. However, a successful observation for a small-body event, where the width of the shadow is much less than the diameter of the Earth, requires an accurate prediction to locate observers in the occultation shadow. To have confidence in the observer's position, the prediction of the shadow path should be accurate to better than one-sixth of the occulting body's diameter giving a 99% chance that an observer placed at the predicted center of the occultation will be within the shadow. For Triton, the required accuracy is about 0.02 arcsec. This poster presents the prediction of the shadow path for the occultation of Tr176 by Triton on 1997 July 18. Well in advance of the event, more than one year, we have transit circle observations of the candidate star which allow us to identify possible observing locations (courtesy of R. C. Stone at the U.S. Naval Observatory). Our most accurate astrometry comes from data, stare frames or strip scans, which image both Tr176 and Triton. Fortunately, Triton passed close by Tr176 in February 1997 affording us an opportunity to observe both the star and Triton well in advance of the event. The analysis of these appulse data recorded at Perth Observatory and Cerro Tololo Inter- American Observatory, as well as strip scans from Lowell Observatory and stare frames from the U.S. Naval Observatory will be presented. This work was supported, in part, by NASA Grants NAG5-3940 at MIT and NAG2-1078, NAGW-1912 and NAGW-5238 at Lowell Observatory.