¹Charles A Schambeau, ¹Yanga R. Fernández, ²Carey M. Lisse, ³Nalin Samarasinha, ⁴Laura M. Woodney
¹Department of Physics, University of Central Florida, Orlando, FL 32816, USA
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723
³Planetary Science Institute, Tucson, AZ 85719, USA
⁴Department of Physics, California State University San Bernardino, San Bernardino, CA 92407

We present a new analysis of Spitzer observations of comet 29P/Schwassmann-Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al., 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 & 8.0 μμm bands and the MIPS 24.0 & 70.0 μμm bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. SW1 was not identified in the 5.8 μμm image from the previous work so its incorporation into this analysis is entirely new. Using the Near Earth Asteroid Thermal Model ( Harris, 1998) resulted in a nucleus radius measurement of R = View the MathML source30.2-2.9+3.7 km and an infrared beaming parameter value of View the MathML sourceη=0.99-0.19+0.26. We also measured an infrared geometric albedo, p5.8p5.8 = 0.5 ±± 0.5. Extrapolating a 0.04 V-band albedo and using a normalized reflectivity gradient S′=14.94±1.09S′=14.94±1.09 [% (1000 Å)−1] ( Duffard et al., 2014) we recover an infrared albedo of p5.8p5.8 = 0.31 in the near infrared consistent with the value recovered from thermal modeling. The dust composition extracted from IRS spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides.

Reference
Schambeau CA, Fernández YR, Lisse CM, Samarasinha N, Woodney LM (2015) A New Analysis of Spitzer Observations of Comet 29P/Schwassmann-Wachmann 1. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.038]
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