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arXiv 2103.06477astro-ph.EP
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P/2016 BA14（PANSTARRS）彗星核的中红外观测

Mid-infrared observations of the nucleus of comet P/2016 BA14 (PANSTARRS)

Takafumi Ootsubo, Hideyo Kawakita, Yoshiharu Shinnaka

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Accepted for publication in Icarus
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摘要：

我们介绍了彗星P/2016 BA 14（PANSTARRS）的中红外观测，这些观测是在UT 2016年3月21.3日获得的，日心和地心距离分别为1.012 au和0.026 au，大约在UT 2016年3月22.6日最接近地球（0.024 au）之前30小时。使用安装在夏威夷Maunakea山顶的8.2米斯巴鲁望远镜上的冷却中红外照相机和光谱仪（COMICS），获得了N波段的低分辨率（$λ$ / $Δλ$ ~250）光谱观测和N波段和Q波段的成像观测，其中使用了四个窄带滤光片（中心波长分别为8.8、12.4、17.7和18.8 $μ$ m）。P/2016 BA 14在不同波长下的空间分布符合点扩散函数。由于彗星距离地球很近，观测到的彗星热辐射主要是来自其核的热辐射，而不是尘埃彗发。在中红外波段观测到的原子核光谱能量分布与温度T~350 K时的普朗克函数一致，P/2016 BA 14的有效直径估计为~0.8 km（假设发射率为0.97）。彗星的标准化发射率光谱显示出类似吸收的特征，这些特征是彗星尘埃彗发中通常发现的无水矿物（如橄榄石和辉石）所不能再现的。相反，光谱特征表明存在大颗粒的层状硅酸盐矿物和有机物质。因此，我们的观测表明，一个被这些加工过的物质覆盖的不活跃的小天体可能是彗星的最终状态。

英文摘要：

We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of 1.012 au and 0.026 au, respectively, approximately 30 hours before its closest approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution ($λ$/$Δλ$~250) spectroscopic observations in the N-band and imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 $μ$m) in the N- and Q-bands were obtained using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14 at different wavelengths are consistent with a point-spread function. Owing to the close approach of the comet to the Earth, the observed thermal emission from the comet is dominated by the thermal emission from its nucleus rather than its dust coma. The observed spectral energy distribution of the nucleus at mid-infrared wavelengths is consistent with a Planck function at temperature T~350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by assuming an emissivity of 0.97). The normalized emissivity spectrum of the comet exhibits absorption-like features that are not reproduced by the anhydrous minerals typically found in cometary dust coma, such as olivine and pyroxene. Instead, the spectral features suggest the presence of large grains of phyllosilicate minerals and organic materials. Thus, our observations indicate that an inactive small body covered with these processed materials is a possible end state of comets.

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