Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2002a&link_type=abstract
American Astronomical Society, DPS meeting #41, #20.02
Astronomy and Astrophysics
Astronomy
Scientific paper
Spectral observations of Comet 2P/Encke were obtained during its close approach in the Fall of 2003 in a continuing effort to characterize its physical properties. Over 100 near-IR spectra were collected on six nights in late October and early November from the NASA Infrared Telescope Facility (IRTF) with the SpeX instrument operated in the low resolution mode. The comet appeared to have very little dust coma during this apparition and so the high signal-to-noise spectral data are thought to be dominated by the physical characteristics of its nucleus. The spectra were obtained over a range of rotational phases and viewing geometries, which allowed separate regions of the comet nucleus to be observed and examined for variations in its reflectance properties.
All the spectra from 2P/Encke span 0.7 to 2.5 microns and demonstrate a featureless spectrum with a red slope and a thermal emission signature. There appears to be a slight decrease in slope at wavelengths longer than 1.3 microns and the thermal emission starts to dominate the reflectance signal at approximately 2.0 microns. Given the small heliocentric distance of 2P/Encke at the time of the observations (r 1.2 AU), the thermal emission suggests that the nucleus has a low albedo, which is consistent with albedo values estimated for this object and those determined for other cometary nuclei. The comet's near-IR reflectance is similar to that obtained from other ecliptic comets (e.g., 162P) and possible comet transition objects (e.g., 944 Hidalgo), but not similar to that of Halley-family comet C/2001 OG108. One of the interesting findings from these data is that there appears to be some subtle variation in the thermal emission from the nucleus over the course of the observations, which does not appear to be compositionally related.
This work is sponsored by NASA Planetary Astronomy Grant #NNX08AO66G.
Abell Paul
Bus Schelte J.
Fernandez Yan R.
Lisse Carey Michael
Schleicher David G.
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