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Timerson B.,International Occultation Timing Association IOTA | Brooks J.,IOTA | Conard S.,IOTA | Dunham D.W.,Moscow Institute of Electronics and Mathematics | And 3 more authors.
Planetary and Space Science

On 2012 January 19, observers in the northeastern United States of America observed an occultation of 8.0-mag HIP 41337 star by the Jupiter-Trojan (911) Agamemnon, including one video recorded with a 36 cm telescope that shows a deep brief secondary occultation that is likely due to a satellite, of about 5 km (most likely 3-10 km) across, at 278 ± 5 km (0.0931") from the asteroid's center as projected in the plane of the sky. A satellite this small and this close to the asteroid could not be resolved in the available VLT adaptive optics observations of Agamemnon recorded in 2003. The outline of Agamemnon is fit well by an ellipse with dimensions 190.6 ± 0.9 km by 143.8 ± 1.5 km. The angular diameter of HIP 41337 was found to be 0.5 ± 0.1 milli-arcsec. After (624) Hektor, this could be the second Jupiter Trojan asteroid known to possess a small satellite. © 2013 Elsevier Ltd. All rights reserved. © 2013 Elsevier Ltd. Source

Dunham D.W.,International Occultation Timing Association IOTA | Herald D.,IOTA | Timerson B.,IOTA | Maley P.,IOTA | And 4 more authors.
Proceedings of the International Astronomical Union

For 40 years, the sizes and shapes of many dozens of asteroids have been determined from observations of asteroidal occultations, and over a thousand high-precision positions of the asteroids relative to stars have been measured. Some of the first evidence for satellites of asteroids was obtained from the early efforts; now, the orbits and sizes of some satellites discovered by other means have been refined from occultation observations. Also, several close binary stars have been discovered, and the angular diameters of some stars have been measured from analysis of these observations. The International Occultation Timing Association (IOTA) coordinates this activity worldwide, from predicting and publicizing the events, to accurately timing the occultations from as many stations as possible, and publishing and archiving the observations. Copyright © 2016 International Astronomical Union. Source

Sicardy B.,University Pierre and Marie Curie | Talbot J.,Occultation Section of the Royal Astronomical Society of New Zealand RASNZ | Meza E.,University Pierre and Marie Curie | Camargo J.I.B.,Observatorio Nacional MCTI | And 71 more authors.
Astrophysical Journal Letters

We present results from a multi-chord Pluto stellar occultation observed on 2015 June 29 from New Zealand and Australia. This occurred only two weeks before the NASA New Horizons flyby of the Pluto system and serves as a useful comparison between ground-based and space results. We find that Pluto's atmosphere is still expanding, with a significant pressure increase of 5 ± 2% since 2013 and a factor of almost three since 1988. This trend rules out, as of today, an atmospheric collapse associated with Pluto's recession from the Sun. A central flash, a rare occurrence, was observed from several sites in New Zealand. The flash shape and amplitude are compatible with a spherical and transparent atmospheric layer of roughly 3 km in thickness whose base lies at about 4 km above Pluto's surface, and where an average thermal gradient of about 5 K km-1 prevails. We discuss the possibility that small departures between the observed and modeled flash are caused by local topographic features (mountains) along Pluto's limb that block the stellar light. Finally, using two possible temperature profiles, and extrapolating our pressure profile from our deepest accessible level down to the surface, we obtain a possible range of 11.9-13.7 μbar for the surface pressure. © 2016. The American Astronomical Society. All rights reserved. Source

Durech J.,Charles University | Kaasalainen M.,Tampere University of Technology | Herald D.,International Occultation Timing Association IOTA | Dunham D.,KinetX, Inc | And 8 more authors.

Asteroid sizes can be directly measured by observing occultations of stars by asteroids. When there are enough observations across the path of the shadow, the asteroid's projected silhouette can be reconstructed. Asteroid shape models derived from photometry by the lightcurve inversion method enable us to predict the orientation of an asteroid for the time of occultation. By scaling the shape model to fit the occultation chords, we can determine the asteroid size with a relative accuracy of typically ∼10%. We combine shape and spin state models of 44 asteroids (14 of them are new or updated models) with the available occultation data to derive asteroid effective diameters. In many cases, occultations allow us to reject one of two possible pole solutions that were derived from photometry. We show that by combining results obtained from lightcurve inversion with occultation timings, we can obtain unique physical models of asteroids. © 2011 Elsevier Inc. Source

Buie M.W.,Southwest Research Institute | Olkin C.B.,Southwest Research Institute | Merline W.J.,Southwest Research Institute | Walsh K.J.,Southwest Research Institute | And 25 more authors.
Astronomical Journal

We present results of a stellar occultation by the Jupiter Trojan asteroid Patroclus and its nearly equal size moon, Menoetius. The geocentric mid-time of the event was 2013 October 21 06:43:02 UT. Eleven sites out of 36 successfully recorded an occultation. Seven chords across Patroclus yielded an elliptical limb fit of 124.6 by 98.2 km. There were six chords across Menoetius that yielded an elliptical limb fit of 117.2 by 93.0 km. There were three sites that got chords on both objects. At the time of the occultation we measured a separation of 664.6 km (0.247 arcsec) and a position angle for Menoetius of 265. Source

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