Occultations by 216 Kleopatra the Dog Bone Asteroid

Occultations by (216) Kleopatra, the “Dog Bone Asteroid” David Dunham IOTA Meeting, Stillwater, Oklahoma 2016 July 30

(216) Kleopatra • (216) Kleopatra is one of the larger M-class (“metallic” spectral characteristics) asteroids. • It also has the largest amplitude (1. 4 mag. ) lightcurve of any main belt asteroid, showing that it must be very elongated. • Hence, there has been great interest in observing occultations by this object since the “modern” era of asteroidal occultation observations began in 1975. • In 1977, based mainly on Paul Maley’s observation of a secondary occultation of 3. 6 -magnitude gamma Ceti by (6) Hebe near Victoria, TX, over 900 km north of Mexico City, where the main event was seen, IOTA started claiming that some minor planets might have satellites. • To most astronomers, this was an outlandish idea, convinced that relatively small asteroids just can’t have satellites. But T. Van Flandern showed that stable orbits exist within about 100 diameters from typical asteroids. • Although some planetary astronomers were persuaded that “maybe” such objects could exist, the fact that virtually all amateur observations then were visual made most astronomers doubt our observations. • To counter the skeptics, IOTA encouraged observations from pairs of stations along the same chord, but separated by at least a 100 m for independent confirmation.

First Occultation, 1980 October 10 -1 An account of this occultation was published in Occultation Newsletter Vol. 2, pages 140 – 141. We knew that it would occur near a minimum of the large-amplitude lightcurve, so we knew it would be end-on to us, the least interesting orientation.

First Occultation, 1980 October 10 - 2 Bottom of p. 140, from the March 1981 issue of Occultation Newsletter.

First Occultation, 1980 October 10 - 3 Top of p. 141, from the March 1981 issue of Occultation Newsletter.

First Occultation, 1980 October 10 - 4 Bottom of p. 141, from the March 1981 issue of Occultation Newsletter.

1980 October 10 fit to Descamps (2010) Shape Model The confirming Rattley-Cooke secondary occ’n remained a curiosity for many years. Brian Marsden & others wanted more than visual data; they remained unconvinced. To this day, their observations are not included in the asteroidal occultation database, although many other observations of occultations by asteroidal satellites, mainly made with video this century, are included.

1991 January 19 fit to Descamps (2010) Shape Model This is the next observed occultation; it confirmed Kleopatra’s extremely elongated shape. Klemola’s updated path passed just north of New York City, and Wayne Warren and I tried to go there, but our departure from Greenbelt, MD was delayed, and we ran into clouds when we approached Newark, NJ, so we observed from the pine barrens south of there. Ours is one of the early video recordings of an asteroidal occultation.

2003 August 10 Elliptical Fit This is the next occultation with more than one chord after 1991. The visual observations were made by relatively inexperienced observers in southern South America. In 2000, JPL’s Steve Ostro reported the radar-determined “dog bone” shape mo

2008 September 26 Elliptical Fit Scotty Degenhardt and I flew to Ft. Nelson, in n. e. British Columbia, to observe this occultation of a 7. 7 -magnitude star with mighty mini’s; it was one of Scotty’s largest deployments (nearly 20 stations), all with a miss due to a huge south shift. Only my 2 southernmost stations recorded the occultation.

2008 September 26 Elliptical Fit Scotty Degenhardt had much better luck for the next event in southern Arizona, recording 8 positives. Joan, William, and I set up nearly as many stations to the west of the predicted center, and they all had no occultation by Kleopatra (but need to check most tapes for a possible satellite event). These seemed to support a more contact binary model with two end-to-end ellipsoids rather than the radar model.

Kleopatra Shape Model, P. Descamps et al. , 2010 The radar “dog bone” shape model, shown in the black boxes above, is shown at the time when Keck 10 m adaptive optics (AO) observations were made in 2009, from Descamps et al’s 2010 paper about Kleopatra.

Kleopatra Satellites, P. Descamps et al. , 2010 Several observations of the satellites were obtained with Keck, allowing their orbits to be determined.

First Occultation, 1980 October 10 After 30 years, Rattley and Cooke’s 1980 observations are finally confirmed, shown by the green dots that are close enough to one of the satellite orbits. Perturbations in 30 years could cause the small offset.

2015 March 12 Elliptical Fit With 46 chords, this is the best-observed occultation by Kleopatra, with 45 chords obtained by western European observers.

2015 March 12 Elliptical Fit This is the event that Joan & I returned home for, now with John Broughton’s paver mounts (although pavers not needed for this event) With 46 chords, this is the best-observed occultation by Kleopatra, with 45 chords obtained by western European observers.

We followed the Occult Watcher plan of 9 stations, all near exits from I-95 in S. Carolina & Georgia We covered the north side of the path, while Roger Venable set up south of it. We had a miss at southernmost Station 9, just n. of the predicted center, so we feared we would have misses. But as we picked up stations on the way north, we saw that they were positive, 6 positives. Unfortunately, we lost observations at the northernmost stations 1 (input chord loose on ZR camcorder) and 2 (MDVR 10 battery pack went flat before event).

2016 April 5 Descamps Model Fit We look forward to Gaia data to improve the path predictions!