Cathy Olkin

 Determine size and shape  This requires multiple chords  With only one chord you only get lower limit on size 2009/11/19 Occultation by Terpsichore (124x112 km), Dunham, Garrett and Desmarais IOTA website

 If we could get a Pluto occultation and a Nix or Hydra occultation by the same star, that would greatly reduced our orbit uncertainty Sicardy et al. 2009

 Multiple chords in small area with large uncertainties

Prediction on July 18 Occultation on July 31, 2007  How well can we predict Pluto occultations?  Only to about 0.5 radius or ~600 km (25 mas)  Usually limited by Pluto position not star position

 Assume diameter = 80 km  Space observers 40 km  Can’t get large telescopes with this spacing => need bright star  To cover 600 km, you would need 15 observers  Only go to dry weather places  Good news: To get shape you can use cheaper equipment

 How uncertain are the Nix and Hydra ephemerides now?  This is on top of the uncertainty in the star relative to the Pluto system From Tholen et al., 2008

Title:Attempted Observations of the 2009 Occultation of a Star by Nix Authors:Pasachoff, Jay M.; Widemann, T.; Sicardy, B.; Lister, T.; Tholen, D. J.; Gulbis, A. A. S.; Adams, E. R.Pasachoff, Jay M.; Widemann, T.; Sicardy, B.; Lister, T.; Tholen, D. J.; Gulbis, A. A. S.; Adams, E. R. Publication:American Astronomical Society, AAS Meeting #214, # Abstract We attempted to observe the predicted 4 March 2009, 13:56 UT, approximately 6-second-long occultation of an 11th magnitude star by Pluto's small moon Nix, which is fainter than 23rd magnitude. In parallel starlight, the path was 88 km in width with a one-sigma range from 44 km to 110 km. The Tycho star is at (J2000.0), and has R=11.8 and K=10.4. The occultation path was predicted to cross the Hawaiian islands, with a southern boundary cutting through Maui and missing the telescopes on Mauna Kea, but the uncertainty in the prediction (1 sigma) was about 500 km (though only 5 minutes in time). The path's speed was 15 km/s. In the event, we obtained data only from the 2-m Faulkes telescope on Maui, with uneven skies. Our trailed images did not show evidence of the occultation, which would have dropped the observed intensity at the merged star/Nix position by about 12 magnitudes or, more likely, if Nix and Pluto were merged by about 3 magnitudes. Weather prevented observations with MegaCam on the CFHT, with a MIT POETS on the IRTF, with PanSTARRS on Maui, as well as with an 0.4-m telescope at Windward Community College on Oahu. For administrative reasons, we did not succeed in obtaining data with the 3.7-m AEOS telescope on Maui. In any case, the event was at low altitude, only 21°, so pointing was at the limits for several of the telescopes.

 Lots of Prospects…  Bruno Sicardy lists 202 Nix occultations in 2010 and 185 Hydra events  sicardy/predic_occn_10/Hydra_2010/g3_occ_data_ hydra_2010_table

 Good weather  Somewhat bright star (V<15), allowing lots of small telescopes  Already deployed for Pluto or Charon event to minimize cost