A Central Flash at an Occultation of a Bright Star by Pluto Soon Before New Horizons' Flyby
Abstract
From the Mt. John Observatory, New Zealand, we were so close to the center of the occultation path on 29 June 2015 UTC that we observed a modest central flash from the focusing of starlight from a 12th-magnitude star. The star was one of the brightest ever in our years of continual monitoring that started in 2002. At the time of Pluto's perihelion in 1989, it was feared from models that Pluto's atmosphere might collapse by now, a motivation for the timely launch of New Horizons; some models now allow Pluto to retain its atmosphere throughout its orbit.We used our frame-transfer CCD at 10 Hz with GPS timing on the 1-m McLellan telescope of Canterbury U. We also observed with a Lowell Obs. infrared camera on the "AAVSO" 0.6-m Optical Craftsman telescope; and obtained 3-color photometry at a slower cadence on a second 0.6-m telescope. We coordinated with the overflight of SOFIA and its 2.5-m telescope, which benefited from last-minute astrometry, and the Auckland Observatory's and other ground-based telescopes.Our light curves show a modest central flash; our tentative geometrical solution shows that we were only about 50 km from the occultation path's centerline. The flash is from rays lower than otherwise accessible in Pluto's atmosphere. Our light curves, at such high cadence that we see spikes caused by atmospheric effects that we had not seen so well since our 2002 Mauna Kea occultation observations, show that Pluto's atmosphere had not changed drastically since our previous year's observations. Our data provide a long-term context for New Horizon's highly-detailed observations of Pluto's atmosphere in addition to providing a chord for the geometrical solution that includes SOFIA's observations.Our observations were supported by NASA Planetary Astronomy grants NNX12AJ29G to Williams College, NNX15AJ82G to Lowell Observatory, and NNX10AB27G to MIT, and by the National Research Foundation of South Africa. We are grateful to Alan Gilmore, Pam Kilmartin, Robert Lucas, and Carolle Varughese for assistance at Mt. John. We thank the AAVSO for use of the AAVSOnet 0.6-m telescope and Arne Henden for assistance.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #47
- Pub Date:
- November 2015
- Bibcode:
- 2015DPS....4721012P