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Mid-Infrared Spectrum of the Nucleus of Comet 2P/Encke

Presentation #322.10 in the session Comets (Poster + Lightning Talk)

Published onOct 23, 2023
Mid-Infrared Spectrum of the Nucleus of Comet 2P/Encke

We observed comet 2P/Encke with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope on UT2003 Nov 12.3, when the comet was at heliocentric and geocentric distances of 1.09 and 0.27 au, respectively. Imaging observations of the comet with narrow-band filters centered at 8.8, 10.5, 11.7, 12.4, 18.8, and 24.5 microns and low-resolution spectroscopic observations in the N-band (8 - 13 microns, R~250) of the comet were performed.

The observed spatial profiles of the comet were consistent with those of a standard star (FWHM ~ 0".3 at 10.5 microns, close to the diffraction-limited image size). Furthermore, the observed N-band spectrum was almost featureless and exhibited no prominent excess emission feature at ~10 microns due to fine silicate grains in the cometary coma. We concluded that the observed spectrum was dominated by thermal emission from the cometary nucleus.

Unfortunately, the night was not in photometric condition, so we cannot constrain the temperature of the nucleus surface. Combined with the Spitzer/IRAC observations of the comet on UT2003 Nov 11.7, the temperature of the nucleus surface could be estimated to be 300 - 370 K, which is consistent with the nominal temperature of a cometary nucleus surface at 1.09 au from the Sun (Suttle et al. 2020). The relative emissivity spectrum of the nucleus shows shallow absorption-like features at ~9.5 and ~10.6 microns, which are also seen in comet P/2016 BA14 (PANSTARRS) (Ootsubo et al. 2021). The origin of these features is discussed.

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