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TARGETED OCCULTATION STUDIES (WITH SOFIA & GROUND BASED TELESCOPES)

TARGETED OCCULTATION STUDIES (WITH SOFIA & GROUND BASED TELESCOPES). Michael J. Person, MIT (Based on Poster 39.07 J. L. Elliot & S. D. Kern) DPS, Kuiper Belt Workshop 2003 September 1. EXAMPLES OF KBOS* WITH ATMOSPHERES. Pluto and Triton Similar sizes and densities N 2 (CO, CH 4 )

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TARGETED OCCULTATION STUDIES (WITH SOFIA & GROUND BASED TELESCOPES)

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  1. TARGETED OCCULTATION STUDIES (WITH SOFIA & GROUND BASED TELESCOPES) Michael J. Person, MIT (Based on Poster 39.07 J. L. Elliot & S. D. Kern) DPS, Kuiper Belt Workshop 2003 September 1

  2. EXAMPLES OF KBOS* WITH ATMOSPHERES • Pluto and Triton • Similar sizes and densities • N2 (CO, CH4) • Atmosphere on Charon? Pluto enhanced Pluto-Charon images from HST. The bodies are separated by 19,400 km (after Albrecht et al. 1994). The Triton image (left) is from Voyager 2. *physical definition

  3. REQUIREMENTS FOR AN ATMOSPHERE 103 102 N2 10 Pressure ( µbar) 1 CO 10–1 Ar 10–2 0.5 flux drop for Triton occultations CH4 Kr 10–3 30 35 40 45 50 55 Temperature (K) • Right temperature • Not too warm • Volatiles escape • Not too cold • Not enough sublimation • Blackbody temperature for 30AU is about 50K • Sufficiently massive • How massive? •  = (GM/k)(mµ/rT) • Mass overcomes escape (e.g. Titan) • Kr atmosphere on less massive objects? • Appropriate surface volatiles • N2, CO, CH4, NH3, Ne, Ar, Kr • Primordial, or replenished (Data from Brown & Ziegler 1980)

  4. OBJECTIVES FOR KBO OCCULTATIONS • Accurate diameters • Calibrate thermal diameters • SIRTF • Sub-millimeter • Search for atmospheres • The largest KBOs may retain atmospheres • Search for binary companions • Models differ on the semi-major axis distribution for KBO binaries

  5. PROSPECTS FOR ATMOSPHERES N2 Atmospheres Ixion Varuna (0.07) 0.04 0.64 log radius (km) Triton (0.75) Pluto (0.53-0.74) Quoar (0.10) Geometric Albedo (V) Charon (0.40) Atmosphere? 8 6 4 2 0 –2 H magnitude

  6. CHARON OCCULTATION (Walker 1980) (after Elliot & Young 1991)

  7. CHIRON OCCULTATION RESULTS Adapted from Elliot et. al. 1995 Nature

  8. TARGETED OCCULTATIONS BY KBOs* Charon 1980 April 7—South Africa Single chord (Walker at SAAO) Pluto 1988 June 9 (P8)-southwestern Pacific KAO and several ground-based sites, 7 successful 2002 July 20 (P126A)-South America Many attempts, only 2 successful 2002 August 21 (P131.1) - Hawaii and western US 9 telescopes successful (2060) Chiron 1993 November 7 (Ch02) - western US Two telescopes successful 1994 March 9 (Ch08) - Brazil KAO successful Triton 1993 July 10 (Tr60) one chord with KAO; 4 ground-based stations, none successful 1995 August 9 (Tr148A, Tr148B) 9 light curves from 6 sites, including the KAO; central flash from IRTF 1997 July 18 (Tr176) 2 chords with C14's; amateur chords too 1997 November 4 (Tr180) central flash with FGS on HST; 1 ground-based site miss; 2 ground-based sites cloudy; Lear jet had problems 2001 August 25 (Tr231) light curve with Sutherland 1.9-m *physical definition

  9. CHALLENGES FOR OCCULTATIONS • aheliocentric distance as of 2003 May 21

  10. KBO RADII FROM OCCULTATIONS • Strategy #1: Small telescopes (0.36 m; fixed or mobile?) • Limiting stellar magnitude 16.2 • Set up network in western US (or Chile & Australia) • At least two occultation chords needed (Dm too large for astrometry?) • Strategy #2: Chase with SOFIA (2.7 m) • Limiting stellar magnitude 18.4 • Need accurate prediction (miss is expensive!) • Second occultation chord or astrometry (from another telescope) • Strategy #3: Large telescope (6.5->10 m ) • Limiting stellar magnitude 19.3 • Initial prediction accurate to 0.025 arcsec (=> 1/5 success rate) • Single occultation chord & astrometry with the same telescope

  11. EVENTS PER YEAR • bfor a single telescope and the current sample of 29 KBOs brighter than an H magnitude of 5.2.

  12. KBO OCCULTATIONS • Objectives • Establish accurate diameters • Search for close companions • Search for atmospheres • Approach • Brightest KBOs as targets • Three strategies (portable, airborne, large fixed) • Needs • Discovery of more bright KBO’s in dense star fields • Star density in the galactic plane ~ 10 times the average • More events per good orbit • Improved orbits, high astrometric precision • 17 orbits better than 0.1"; 79 better than 1" • How much large telescope time to use for predictions vs. observations? Ch08 prediction, 1994 March 9: observations made with the KAO& from South Africa (SAAO)

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