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 –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)

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, ) –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, detected –See Grundy et al. Talk  J. Spencer – Binary TNOs (Cycle 1-2, ) –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

Spitzer Sample: Orbital Elements

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…

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

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

Data Massage (24  m) Orcus/ um, M. Brown data Typical mosaic with effects of scattered light and Latents Same mosaic after correction subtractdivide

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

Sky Subtraction (24  m) um, 2000sec. J. Spencer data F 24 = 0.1 mJy Straight MosaicSky Subtracted

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

Sedna 40 mJy background source

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

Sedna: Size and Albedo  Adopt 2 mJy as upper limit –Best image gives 0.7 mJy, 1-  70um  Size depends on Sedna’s thermal state (fast- or slow- rotator) –Likely to favor fast-rotator (43K T BB at 90 AU)  Featureless spectrum Trujillo et al 2005 –Not a planetoid: D 12%  Lack of volatile ices –Low albedo: p V 1200km STM limit ILM limit (ILM) (STM)

2003 UB313 August sec 24um exposures sec 70um exposures 24um, 8000 sec super-sky

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

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

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.

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 –p V > about 70%  New, better data expected soon

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

2005 FY9  Volatile ices suggest complex surface  2-terrain model required to fit thermal data –Diameter ~1600 km –p V ~ 80%

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

Results To Date