Bruno Sicardy Obs. Paris - LESIA and occcultation Team Thomas Widemann

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1 PHYSIQUE DE L'ATMOSPHÈRE DE PLUTON ET TAILLE DE CHARON DÉDUITES D'OCCULTATIONS STELLAIRES 2002-2006
Bruno Sicardy Obs. Paris - LESIA and occcultation Team Thomas Widemann François Colas Atelier 3ème zone, Nantes janvier 2007

2 probed by occultations
Pluto and Charon probed by occultations  special moment: equinox in 1988, perihelium in 1989 (period 248 years)  effects on N2 pressure-equilibirum atmosphere?  Charon's size? ( density ?)  Charon's surface gravity ~ 1/2 Pluto's gravity  possibility of atmosphere?

3 complex interplay of large distance
variations & drastic seasonal effects C.J Hansen & D.A. Paige Icarus, 120, (1996)

4 2001 2011 2020 Pluto motion in the sky

5 Pluton 20 juil. 2002

6 P August 21, 2002

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13 temperature contrast:
Sicardy et al. Nature, 10 July 2003 spikes: scintillation in Pluto’s atmosphere warmer near pole temperature contrast: cooler near equator

14 Sicardy et al. Nature, July 2003
Imm. Eme. 

15 Sicardy et al. « Large changes in Pluto’s atmosphere as revealed by recent stellar occultations » Nature, 10 July 2003

16 2006 ? 2002 pressure doubled! 1988

17 rP 1988 B'P 2002 2006 rN Time

18 10 bar 1 bar 0.1 bar 1900 2000 2100 C.J Hansen & D.A. Paige
Icarus, 120, (1996)  10 bar  1 bar 0.1 bar 1900 2000 2100

19 Pluto in 1988

20 Pluto in 2002

21 measuring Charon

22 0.89" 2UCAC (D. Herald, Aug. 2004)

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24 VLT/NACO K band, Charon occultation 11 July 2005
Pluto 1" star + Charon

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28 R= 603.61.4 km Sicardy et al., Nature 439, 52, 2006
« Charon’s size and an upper limit on its atmosphere from a stellar occultation »

29 100 K - CH4 56 K - N2 56 K

30 Atmosphere: limit is model dependent, e.g.
Some conclusions: Atmosphere: limit is model dependent, e.g. CH4 with inversion layer: psurf < 15 nbar …or… N2 isothermal 56 K: psurf < 110 nbar etc… Charon’s size: RC =  1.4 km Charon’s density: C = 1.65  0.06 g cm-3 (taken from Buie et al. AJ. 132, 290, 2006, NB. P = 2.03  0.06 g cm-3 for Pluto) Possibility to retrieve Pluto’s radius with accurate Charon’s accurate size --> refine atmospheric model cf. The Astronomical Journal, 132: , 2006 July ORBITS AND PHOTOMETRY OF PLUTOﾕS SATELLITES: CHARON, S/2005 P1, AND S/2005 P2 M. W. Buie, W.M. Grundy, E. F. Young, L. A. Young, A. Stern Barre d'erreur plus grande que ce que je trouve?

31 recent & future stuff…

32 12 June 2006 Pluto occultation

33 1988 2002

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38 12 June 2006, Australia Stockport Blue Mountains Hobart

39 Stockport 50 cm 20 cm Blue Mountains 40 cm Hobart Time (sec UT)

40 99.7% c.l. 2 68.3% c.l. pressure expansion factor since 2002

41 1988 2002

42 2006

43 10 5 2 1 pressure @ 1215 km (bar) time (year) Hansen & Paige,
Icarus 120, 247 (1996) 10 1 5 2 New Horizon 2006 2002 1988 time (year)

44 2007: four Pluto & co events?

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46 Nix, 22 mars 2007

47 Hydra 2.1"

48 Pluto **et** Hydra 12 mai 2007 Paranal & La Silla Pluton 14 juin 2007 Paranal, La Silla & SOAR

49 en cours: prédictions d'occultations par de gros TNO Eris, 2005 FY9, 2003 EL6, Sedna, Orcus, Quaoar, Varuna, … (voir présentation T. Widemann)

50 … merci Paranal Jul 2005

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53 a tenuous atmosphere: Pluto