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J to M spectroscopy of Pluto and Charon

J to M spectroscopy of Pluto and Charon. A Status Report on On-Going Work. S. Protopapa,H. Boehnhardt (MPS, Katlenburg-Lindau) T. Herbst (MPIA, Heidelberg) W. Grundy, J.Spencer (Lowell Obs. Flagstaff) Stern (SWRI Boulder) E. Grün (MPIK H eidelberg). Catania – July, 2006.

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J to M spectroscopy of Pluto and Charon

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  1. J to M spectroscopy of Pluto and Charon A Status Report on On-Going Work • S. Protopapa,H. Boehnhardt • (MPS, Katlenburg-Lindau) • T. Herbst (MPIA, Heidelberg) • W. Grundy, J.Spencer (Lowell Obs. Flagstaff) • Stern (SWRI Boulder) • E. Grün (MPIK Heidelberg) Catania – July, 2006

  2. Surface Ices on Pluto and Charon Known from spectroscopy: Pluto (separated; Owen et al 1993) JHK bands: N2, CH4, CO Charon (separated; Buie et al 1987) JHK bands: H2O Pluto+Charon (combined; Grundy at al 2002) L band: CH4, N2, CO, tholin, H2O, SO2, CO2 M band: not measured Problem of observations: sensitivity of the telescope/instrument (4m class telescopes) resolving the Pluto/Charon binary (seeing limited, work-around occultation measurments)

  3. New Pluto/Charon observations @ UT4-Kueyen+NACO (ESO VLT Paranal/Chile) larger aperture (8.2m) adaptive optics using natural guide stars almost diffraction limited (0.07”K band 0.14” M band) Pluto/Charon as natural guides star wide wavelength range (JHKLM) at low spectral resolution (80-200) still a time consuming task (3-4 nights) Observing run: 3-8 August 2005 (target visibility ~ 6h per night) New spectroscopy of Pluto and Charon

  4. Spectroscopic Calibration, Challenges • Background Subtraction: IR images are pair-wise subtracted with the object offset to distinct regions of the detector • Flat correction • Alignment and coaddition to increase S/N • Solution of problems related to the atmosphere and calibration: Wavelength Calibration Spectra of solar analogs for the correction of the atmospheric features. Subtraction of the solar features. Absence of an arc lamp in L and M band. Atmospheric features for the calibration of the dispersion of the prism comparison with the atmospheric features of the sky background. Curvature correction

  5. Result Pluto geometric albedo λ(Ǻ)

  6. Comparison L band NACO data Pluto IRTF data model geometric albedo λ(Ǻ)

  7. What about M band ? Pluto geometric albedo ? λ(Ǻ)

  8. Results Pluto Charon geometric albedo λ(Ǻ)

  9. E N Charon [r,θ] V S/2005 P1 [r,θ] V S/2005 P2 [r,θ] V Date UT May 2005 Pluto [r,θ] V 15.045 18.141 [0,0] 14.12±0.08 [0,0] 14.12±0.08 [0.834,176.77] 16.22±0.10 [0.855,355.04] 16.22±0.10 [1.85,264.21] ... [2.36,305.76] 22.93±0.12 [2.09,326.94] 23.38 ±0.17 [2.22,355.51] ... Search for P1 and P2 moonlets 2005-05-15 HST 2005-05-18 HST 3.1 days S E 2005-08-03 VLT P2 81 days W P1 N

  10. Conclusions • L band spectroscopy of Pluto • Good agreement between model and Pluto´s spectrum • Deviations between the our and Grundy‘s spectrum (maybe due to different rotation phase of Pluto) • Drop beyond 4.2 μm, as in Grundy´s spectrum •  M band spectroscopy of Pluto • Signal in M band spectrum that deviates from SPITZER photometry •  L band spectroscopy of Charon • First L band Charon´s spectrum that suggests presence of further water absorption band • Future work: do better in M band, consolidate JH bands  Interpretation:modelling of the spectra, looking for rotation phase dependencies

  11. Thank you!

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