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Session 72 - Comet Hale-Bopp.
Display session, Friday, January 09
We present 7.8 - 13.3 \micron \ spectrophotometry and near infrared (IR) images of the dust and inner coma of comet C/1995 O1 (Hale-Bopp). The imaging covers 3 temporal epochs from 1996 June through 1997 February, while the spectrophotometry (R \simeq 350 - 180) covers 4 epochs from 1996 October through 1997 June.
The 10 \micron \ spectra exhibit strong emission peaks at 9.3 \micron, 9.9 - 10.1 \micron, and 11.2 \micron, and weak peaks at 10.5 \micron \ and 11.9 \micron. Decomposition of the observed silicate emission feature into mineral components derived through comparison of Q_ext derived from the cometary spectra to laboratory measurements of terrestrial silicate minerals and interplanetary dust particles suggests that the primary mineral species are olivines and pyroxenes, with a small amount of layer-lattice silicates. The olivines are the more prominent emission species at larger heliocentric distances than the pryroxenes, and empirical analysis shows that the olivines are relatively iron rich while the pyroxenes are magnesium rich. Analysis of the observed 10 \micron \ silicate features indicate that smaller grains were present in the inner coma close to and at perihelion than at larger heliocentric distances (cf., Williams et al. 1997, ApJ 489, L91). The number population of small grains after perihelion at 1.6 AU is roughly equal to that at 2.7 AU before perihelion suggesting that the reservoir of small grains appears exhausted upon passage close to the sun (Wooden et al. 1997, ApJ, in press). The IR imaging detail the change in spatial morphology of the comet as it approached perihelion. Broadband JHK images taken at each of the 3 epochs reveal the appearance and disappearance of sunward and anti-sunward jets, and a surface brightness that falls as \rho^-1. We also present preliminary results of broadband L^\prime\prime and M^\prime and 3.28\micron \ CVF images taken in 1997 February which measure the thermal emission from the dust.
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