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Spitzer Thermal Radiometry of TNOs

Spitzer Thermal Radiometry of TNOs. John Stansberry Will Grundy John Spencer Mike Brown Dale Cruikshank. Overview. Spitzer TNO projects and sample Multiband Imaging Photometer for Spitzer (MIPS) Characteristics Data processing Data and Results for Particular Objects

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Spitzer Thermal Radiometry of TNOs

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  1. Spitzer Thermal Radiometry of TNOs John Stansberry Will Grundy John Spencer Mike Brown Dale Cruikshank

  2. Overview • Spitzer TNO projects and sample • Multiband Imaging Photometer for Spitzer (MIPS) • Characteristics • Data processing • Data and Results for Particular Objects • 2003 UB313, Sedna, 2005 FY9, Huya • Binaries 1999 TC36, 1998 SM165 • Summary • Some other Spitzer results at this conference • Lellouch et al. (Pluto thermal lightcurve) • Grundy et al. (Classical TNO albedos) • Emery et al. (3-10um reflectance) • Bauer et al. (coma of Echeclus) • Spencer et al. (Density of 1998 SM165) (poster)

  3. Spitzer TNO Radiometry Summary • Total GTO – Cycle 2 Sample: 64 TNOs, 13 Centaurs (a < 30AU) • Cruikshank/Rieke – “Bright” TNOs and Centaurs (GTO, 2003) • 13 Centaurs, 31 TNOs • 14 detected at both 24 & 70um with good SNR • TNO Albedos 10% (5% - 20%) • Centaur Albedos 5% (2.5% - 7%) • Beaming parameters ~ 0.7 – 1.8 : thermal inertia important • M. Brown – Icy Planetoids (Cycle 1-2, 2004-2005) • 13 TNOs, ~ ½ detected at both 24 & 70um with good SNR • SEDs consistent with bright and dark terrains for largest objects • W. Grundy – Classical-Belt TNOs (Cycle 1, 2004) • 15 TNOs, 8 - 10 detected • See Grundy et al. Talk • J. Spencer – Binary TNOs (Cycle 1-2, 2004-2005) • 5 targets, 2 detected • See Spencer et al. Poster • Final GTO – Cycle 2 Tally Likely to be ~24 TNOs, 10 Centaurs, 5 Binaries • Cycle 3 (2006) will add ~12 TNOs, 8 Centaurs, 1 Binary

  4. Spitzer Sample: Orbital Elements

  5. MIPS Overview • Multiband Imaging Photometer for SIRTF Spitzer • 24, 70 and 160 micron channels • IFOV 5’x5’, 2.5’x5’, 5’x1’ • Arrays operate at  5K, telescope at 5 – 10K • 24um (23.68 m , 6.5 beam) • 128 x 128 InSb array • Faint limit ~30 Jy (moving targets only) • 70um (71.42 m , 20 beam) • 32 x 32 Ge:Ga photoconductor array • 1/2 of the array suffers from high noise due to cabling issues • Faint limit ~1-2 mJy • 160um (156 m, 40 beam) • 20 x 2 stressed Ge:Ga photoconductor array • 5 dead pixels (contiguous) due to cabling issue • Faint limit ~90 mJy – only useful for Pluto…

  6. Ge:Ga Data • Responsivity is not constant for Ge:Ga detectors • Calibration sources track the changing responsivity • Cal. sources flashed every ~100sec during data taking • 10 sky images between cal. images • Responsivity of each pixel determined by interpolation of cal. sources 70um response vs. time, ground test

  7. The MIPS Calibration Engelbracht et al. 2006, in prep. Gordon et al. 2006, in prep. 70um: Absolute calibration good to 8% (Stars) (Repeatability is better than 7%) 24um: Repeatability is better than 1% (Absolute calibration good to 4%: Stars) Stansberry et al. 2006, in prep. 160um: Absolute calibration good to 12% (Asteroids) (Repeatability is better than 10%)

  8. Data Massage (24m) subtract divide Same mosaic after correction Typical mosaic with effects of scattered light and Latents Orcus/2004 DW @ 24um, M. Brown data

  9. Super-Sky Mosaics (24m) Individual Visits Super-Sky Image NaN out the Source, Coadd in Sky Coordinates Quaoar @ 24um, W. Grundy data

  10. Sky Subtraction (24m) Straight Mosaic Sky Subtracted 1998 SM165 @ 24um, 2000sec. J. Spencer data F24 = 0.1 mJy

  11. Sedna Spitzer’s first Director’s proposal for a Solar System object (M. Brown): 2003 VB12 / Sedna 1 month past end of commissioning (2004-1-28) 70um, 2500sec exposure

  12. Sedna 40 mJy background source

  13. Sedna Sky Subtracted Images 5.2 1.2 mJy 1 = 0.7 mJy

  14. STM limit ILM limit Sedna: Size and Albedo • Adopt 2 mJy as upper limit • Best image gives 0.7 mJy, 1- noise @ 70um • Size depends on Sedna’s thermal state (fast- or slow-rotator) • Likely to favor fast-rotator (43K TBB at 90 AU) • Featureless spectrumTrujillo et al 2005 • Not a planetoid: D < 2000 km, pV > 12% • Lack of volatile ices • Low albedo: pV < 30%, D > 1200km (ILM) (STM)

  15. 2003 UB313 24um, 8000 sec super-sky • August 2005 • 2 4000 sec 24um exposures • 2 5000 sec 70um exposures

  16. 2003 UB313 2nd Visit, sky subtracted 1st Visit, sky subtracted 0.03 mJy source 1 noise < 0.01 mJy/beam

  17. 2003 UB313 70um normal and sky-subtracted images, both epochs. 1 noise 0.75 mJy/beam Adopt 2.5 mJy for Xena

  18. 2003 UB313: Size and Albedo Neither the STM nor Fast-Rotator seem to describe the spectrum of 03UB313… 1.2mm data from Bertoldi et al. 24um data plotted incorrectly: Should be 0.03 mJy.

  19. 2003 UB313: Size and Albedo • UB313 is complex • Volatile ices • Extreme seasonal cycle • Pluto/Triton good analogs • Simple thermal models don’t fit • 2-Terrain model comes close • Diameter < about 2600km • pV > about 70% • New, better data expected soon

  20. 2005 FY9 24um: 800 sec 70um: 400 sec

  21. 2005 FY9 • Volatile ices suggest complex surface • 2-terrain model required to fit thermal data • Diameter ~1600 km • pV ~ 80%

  22. 1999 TC36 1998 SM165:  = 0.5 g/cc (Spencer’s poster) 2003 FX128, 2000 CR46 (Centaurs) in the works. 2003 EL61:  = 3  0.3 g/cc

  23. Results To Date

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