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Trio of Stellar Occultations by Pluto One Year Prior to New Horizons' Arrival

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Journal Article

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US Naval Observatory Flagstaff United States

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We observed occultations by Pluto during a predicted series of events in 2014 July with the 1 m telescope of the Mt. John Observatory in New Zealand. The predictions were based on updated astrometry obtained in the previous months at the USNO, CTIO, and Lowell Observatories. We successfully detected occultations by Pluto of anR18 mag star on July 23 142332 000004 UTC to 142530 000004 UTC, with a drop of 75 of the unocculted stellar signal, and of an R17 star on July 24 114130 000008 UTC to 114328 000008UTC, with a drop of 80 of the unocculted stellar signal, both with 20 s exposures with our frame-transfer Portable Occultation, Eclipse, and Transit System. Since Pluto had a geocentric velocity of 22.51 km s1 on July 23 and 22.35 km s1 on July 24, these intervals yield limits on the chord lengths surface and lower atmosphere of2700130 km and 2640250 km, respectively, indicating that the events were near central, and thereforeprovide astrometric constraints on the prediction method. Our coordinated observations with the 4 m AAT in Australia on July 23 and the 6.5 m MagellanClay on Las Campanas, the 4.1 m Southern Astrophysical Research Telescope on Cerro Pachn, the 2.5 m DuPont on Las Campanas LCO, the 0.6 m SARA-South on Cerro Tololo of the Southeastern Association for Research in Astronomy SARA, the MPIESO 2.2 m on La Silla, and the0.45 m Cerro Caln telescope and 0.36 telescope in Constitucin in Chile on July 27 and 31, which would have provided higher-cadence observations for studies of Plutos atmosphere, were largely foiled by clouds, but led to detection with the LCO MagellanClay and DuPont Telescopes on July 31 of the grazing occultation of apreviously unknown 15th-magnitude star, completing the trio of occultations successfully observed and reported in this paper.

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