Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...191.7206h&link_type=abstract
American Astronomical Society, 191st AAS Meeting, #72.06; Bulletin of the American Astronomical Society, Vol. 29, p.1319
Astronomy and Astrophysics
Astronomy
1
Scientific paper
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 =~ 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 Qext 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('') and M(') and 3.28\micron \ CVF images taken in 1997 February which measure the thermal emission from the dust.
Butner Harold M.
Forrest William John
Goetz Jennifer A.
Harker David E.
Koike Chiyoe
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