Mid-infrared observations of P/2016 BA14 (PANSTARRS) during its close approach to Earth: Thermal emission spectrum of the cometary nucleus

Comet P/2016 BA₁₄ (PANSTARRS) made its closest approach to Earth (0.024 au) on UT 2016 March 22.6 while we conducted mid-infrared observations of the comet on UT 2016 March 21.3, at heliocentric and geocentric distances of the comet, 1.01 au and 0.026 au, respectively. Low-resolution (R ~ 250) spectroscopic observations in N-band and imaging observations with narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 microns) in N- and Q-bands were carried out by the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop of Maunakea, Hawaii. Spatial profiles of P/2016 BA₁₄ at different wavelengths are consistent with those of a spectrophotometric standard star (a point source) and we concluded that the observed thermal emission from the comet is dominated by the thermal emission from its nucleus, not from dust coma as usual. Thanks to the close approach of the comet to Earth, we could observe thermal emission from the nucleus even from the ground-based observatory. In the normalized emissivity spectrum of P/2016 BA₁₄, some emissivity features could be recognized, but not easily identified as minerals usually found in cometary dust coma, such as olivine and pyroxene in amorphous or crystalline phase. A few features may be attributed to complex organic materials.