Pluto occultation on 2015 June 29 UTC with central flash and atmospheric spikes just before the New Horizons flyby

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2017-11, Vol.296, p.305-314
• Main Authors: Pasachoff, Jay M., Babcock, Bryce A., Durst, Rebecca F., Seeger, Christina H., Levine, Stephen E., Bosh, Amanda S., Person, Michael J., Sickafoose, Amanda A., Zuluaga, Carlos A., Kosiarek, Molly R., Abe, Fumio, Nagakane, Masayuki, Suzuki, Daisuke, Tristram, Paul J., Arredondo, Anicia
• Format: Article
• Language: English
• Subjects: Occultations; Photometry; Pluto, atmosphere
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2017.05.012

•We observed an occultation of the brightest star ever in our series of Pluto occultations, 12th magnitude.•The event was only about two Pluto-days (and 15 Earth-days) before the flyby of NASA's New Horizons spacecraft.•Our observations from the Mt. John Observatory and Auckland in New Zealand were simultaneous to SOFIA observations with its 100-inch telescope and occultation photometer HIPO, overflying not far from Mt. John.•At Mt. John, with the 1-m telescope, we were so close to the center of the occultation that we observed a central flash, enabling us to study the atmosphere close to the limb than ever before.•We observed a number of bright spikes in the light curve during ingress and egress from both Mt. John and Auckland, showing structure in Pluto's atmosphere.•With the subsequent determination of Pluto's size from New Horizons, we have a more accurate scale for the atmosphere than from previous occultation observations. We observed the occultation by Pluto of a 12th magnitude star, one of the two brightest occultation stars ever in our dozen years of continual monitoring of Pluto's atmosphere through such studies, on 2015 June 29 UTC.At the Univ. of Canterbury Mt. John Observatory (New Zealand), under clear skies throughout, we used a POETS frame-transfer CCD at 10Hz with GPS timing on the 1-m McLellan telescope as well as an infrared camera on an 0.6-m telescope and three-color photometry at a slower cadence on a second 0.6-m telescope. At the Auckland Observatory, we used a POETS and a PICO on 0.5-m and 0.4-m telescopes, with 0.4s and 2s cadences, respectively, obtaining ingress observations before clouds moved in. The Mt. John light curves show a central flash, indicating that we were close to the center of the occultation path. Analysis of our light curves show that Pluto's atmosphere remains robust.The presence of spikes at both sites in the egress and ingress shows atmospheric layering. We coordinated our observations with aircraft observations (Bosh et al., 2017) with the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our chords helped constrain the path across Pluto that SOFIA saw. Our ground-based and airborne stellar-occultation effort came only just over two weeks of Earth days and two Pluto days before the flyby of NASA's New Horizons spacecraft.