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M. S. Kelley, C.E. Woodward, T.J. Jones (U. Minn.)
We present near-infrared (2.2\mum) imaging polarimetry for six comets during their recent apparitions obtained at the NASA IRTF (+NSFCAM). Our observations of short period comets 10P/Tempel 2, 19P/Borrelly, 55P/Tempel-Tuttle, 103P/Hartley 2, and dynamically new, long period comets C/2000 WM1 (LINEAR) and C/2001 A2 (LINEAR), significantly increase the total number of IR polarimetric measurements of comets. We find the 2.2\mum polarization versus phase curve is approximately 1-2% greater than values typically determined from R-band (optical) polarization measurements, suggesting a general, but weak, trend of higher polarizations at wavelengths longer than 0.7\mum. For comet C/1995 O1 (Hale-Bopp), the polarization at 40\circ phase angle varies by only about a factor of 1.6 from 0.3 - 2.2\mum, and is nearly flat from 0.7 - 2.2\mum. Any model of comet dust must reproduce the observed weak wavelength dependence of polarization. For our six comets, no significant grain population gradient is evident in our polarization maps, suggesting the grains remain intact with time and the jets contain a grain population similar to those in the coma. We simulate observations of comets 10P/Tempel 2 and 19P/Borrelly with dynamic modeling of a non-disintegrating grain population (using independently determined rotation axes and jet ejection velocities) and can reproduce the observed spatial distribution of the dust and jet structure in our images.
Acknowledgments: This research was supported in part by a National Science Foundation grant to the University of Minnesota.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.