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Limits on Pluto’s Small Companions

Limits on Pluto’s Small Companions. Andrew Steffl (SwRI) Max Mutchler ( STScI ) With thanks to Marc Buie, Dan Durda, Bill Merline, John Spencer, Alan Stern, Dirk Terrell, Hal Weaver, Eliot Young, and Leslie Young. Historical Satellite Searches. Tombaugh (1960)

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Limits on Pluto’s Small Companions

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  1. Limits on Pluto’s Small Companions Andrew Steffl (SwRI) Max Mutchler (STScI) With thanks to Marc Buie, Dan Durda, Bill Merline, John Spencer, Alan Stern, Dirk Terrell, Hal Weaver, Eliot Young, and Leslie Young

  2. Historical Satellite Searches • Tombaugh (1960) • No satellites detected (published no formal upper limits) • Kuiper (1961) • mp= 19 for 0.3”- 2” from Pluto • mp = 22.4 for > 2” from Pluto • Stern et al. (1991) • m(90%) = 20.6±0.5 for 6”-10” • m(90%) = 22.6 for > 10” from Pluto • Stern et al. (1994) • mV(90%) = 21.7 for 1”-2” from Pluto • mV(90%) = 21.9 for 2”-10” • Nicholson & Gladman (2006) • mR(50%) = 25.0±0.2 for > 4” from Pluto

  3. Motivation for a new Satellite Search • Pluto’s Hill sphere is big • rH = 6 x 106 km (4.6’ from earth) • Charon located at ≈ 0.003 rH • However, orbits near the edge of Hill sphere are not stable over the age of the solar system • Szebehely’s stability criterion r < ⅓rH • Hamilton & Krivovr < 0.53rH (pro.) r < 0.69 rH(retro) • Nesvornýr < 0.4 rH (pro.) r < 0.7rH(retro) • Stern et al. (1994) limit corresponds to 85 km object

  4. HST Campaign of 2005 • 2 visits of 1 orbit using ACS/WFC • 2005 May 15 and 2005 May 18 • 1 0.5s image • 4 475s images • After discovery of Nix & Hydra obtained 2 additional visits with ACS/HRC • 2006 Feb 16 • 2006 Mar 02

  5. Flatfielded ACS/WFC Data

  6. Data Analysis • 400 artificial PSFs with 25.5 ≥ mV ≥ 29.5 placed randomly within WFC field • Median combine images using “drizzle” software • Visually identify objects in field • Compare found objects to list of added PSFs • Nix and Hydra detected in this way

  7. 2005 May 15

  8. 2005 May 15 with PSFs

  9. A note on detection efficiency mV = 26.8 90% detection limit mV = 27.4 50% detection limit HRC 3”-5” 50% detection limits are often quoted in the literature Advantages: common, well-defined Disadvantages: Usefulness?

  10. 2006 Feb 16 ACS/HRC

  11. ACS/HRC with mV = 25 PSFs

  12. ACS/HRC with random PSFs

  13. Detection Limit vs. Radial Distance

  14. Size Limits of Satellites 90% Limit

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