Presentation on theme: "Spitzer Thermal Radiometry of TNOs John Stansberry Will Grundy John Spencer Mike Brown Dale Cruikshank."— Presentation transcript:
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: 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 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