High polarization degree of the continuum of comet 2P/Encke based on spectropolarimetric signals during its 2017 apparition
High polarization degree of the continuum of comet 2P/Encke based on spectropolarimetric signals during its 2017 apparition
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基于 2017 年彗星出现期间的分光偏振信号的 2P/恩克彗星连续谱的高偏振度
DOI：
10.1051/0004-6361/201833968
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发表时间：
2018
影响因子：
6.5
通讯作者：
Akitaya H.
中科院分区：
文献类型：
--
作者：
Kwon Y. G.;Ishiguro M.;Shinnaka Y.;Nakaoka T.;Kuroda D.;Hanayama H.;Takahashi J.;Baar S.;Saito T.;Kawabata M.;Uemura M.;Morokuma T.;Murata K. L.;Takagi S.;Morihana K.;Nagayama T.;Sekiguchi K.;Kawabata K. S.;Akitaya H.
背景光谱偏振法是一种强有力的技术，用于研究彗星彗星中气体和固体物质的物理性质，而不会相互污染，但只有少数光谱偏振法研究已经进行了提取每种成分。彗星2 P/Encke的偏振度，不受分子发射的影响。该目标的独特之处在于，它的轨道与木星动态脱钩，就像主带小行星一样，方法我们在UT 2017年2月21日使用广岛光学和近红外相机观察彗星，该相机连接到UT 2017年2月21日的150 cm金田望远镜的卡塞格伦焦点上，当时彗星处于太阳相位角α= 1.0 °。结果在0.82μm有效波长处，相对于散射面的连续偏振度为P_（max），r= 33.8 ± 2.7%，明显高于相位角相近的高P_（max）组彗星尘埃的偏振度。假设2 P/Encke尘埃的偏振响应与其它彗星的偏振响应在形态上相似，则在αmax <$100 °时，其最大偏振度为Pmax <$40%。此外，我们还得到了C_2Swan带（0.51-0.56μm）、NH_2 α带（0.62-0.69μm）和CN-红体系（0.78-0.94μm）的偏振度在3- 19%范围内的变化，这些变化依赖于各分支的分子种类和转动量子数.在0.50-0.97μm.ConclusionsFrom观测证据，我们推测2 P/Encke的高偏振度可能归因于核周围的大尘埃颗粒占主导地位，这些颗粒在太阳附近频繁的近日点通道后仍然存在。
ContextSpectropolarimetry is a powerful technique for investigating the physical properties of gas and solid materials in cometary comae without mutual contamination, but only a few spectropolarimetric studies have been conducted to extract each component.AimsWe attempt to derive the continuum (i.e., scattered light from dust coma) polarization degree of comet 2P/Encke, free of the influence of molecular emissions. The target is unique in that its orbit is dynamically decoupled from Jupiter, like the main-belt asteroids, but it ejects gas and dust like ordinary comets.MethodsWe observed the comet using the Hiroshima Optical and Near-Infrared Camera attached to the Cassegrain focus of the 150 cm Kanata telescope on UT 2017 February 21 when the comet was at the solar phase angle ofα= 75°.7.ResultsWe find that the continuum polarization degree with respect to the scattering plane isPcont, r= 33.8 ± 2.7% at the effective wavelength of 0.82μm, which is significantly higher than those of cometary dust in a high-Pmaxgroup at similar phase angles. Assuming that an ensemble polarimetric response of the dust of 2P/Encke as a function of phase angle is morphologically similar with those of other comets, its maximum polarization degree is estimated toPmax≳ 40% atαmax≈ 100°. In addition, we obtain the polarization degrees of the C2swan bands (0.51–0.56μm), the NH2αbands (0.62–0.69μm), and the CN-red system (0.78–0.94μm) in a range of 3–19%, which depend on the molecular species and rotational quantum numbers of each branch. The polarization vector is aligned nearly perpendicularly to the scattering plane with an average of 0°.4 over a wavelength range of 0.50–0.97μm.ConclusionsFrom the observational evidence, we conjecture that the high polarization degree of 2P/Encke might be attributable to a dominance of large dust particles around the nucleus, which have remained after frequent perihelion passages near the Sun.