67 P彗星尘埃彗发的VIRTIS-H观测：光谱特性和色温随相位和高度的变化
VIRTIS-H observations of comet 67P's dust coma: spectral properties and color temperature variability with phase and elevation
摘要：
我们分析了2015年6月3日至10月29日在日心距离r_h = 1.24-1.55 AU处使用罗塞塔上的VIRTIS-H仪器获得的67 P/Churyumov-Gerasimenko彗星尘埃彗发的2-5微米光谱观测。使用光谱拟合测量2-2.5微米的颜色、热辐射计的色度和色温。在α = 90°太阳相位角下获得的数据表明，随着高度的增加（0.5至8公里），热辐射的增加（0.05至0.14），伴随着颜色和色温的可能边际下降。可能的解释包括内彗发中存在弹道轨道上的暗粒子，以及粒子成分的径向变化。在50-120°的相位角范围内，相位红化是显著的（0.031%/100 nm/°），在α = 90°时平均颜色为2%/100 nm，这可能与尘埃颗粒的粗糙度有关。此外，还观察到色温随着相位角的减小以约0.3 K/°的速率降低，这与大的多孔颗粒的存在一致，具有低热惯性，并且显示出显著的昼夜温度对比。比较在固定相位角（α = 90°）下获得的数据，在近日点附近观察到20%的热辐射增量。在分析的时间段内，尘埃颜色的日心变化并不显著。测得的色温从260 K变化到320 K，在r_h = 1.24-1.5 AU范围内遵循r^0.6的变化，接近预期的r_h^0.5值。
英文摘要：
We analyze 2-5 micrometre spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the VIRTIS-H instrument onboard Rosetta from 3 June to 29 October 2015 at heliocentric distances r_h = 1.24-1.55 AU. The 2-2.5 micrometre color, bolometric albedo, and color temperature are measured using spectral fitting. Data obtained at alpha = 90° solar phase angle show an increase of the bolometric albedo (0.05 to 0.14) with increasing altitude (0.5 to 8 km), accompanied by a possible marginal decrease of the color and color temperature. Possible explanations include the presence in the inner coma of dark particles on ballistic trajectories, and radial changes in particle composition. In the phase angle range 50-120°, phase reddening is significant (0.031 %/100 nm/°), for a mean color of 2 %/100 nm at alpha = 90°, that can be related to the roughness of the dust particles. Moreover, a decrease of the color temperature with decreasing phase angle is also observed at a rate of ~ 0.3 K/°, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (alpha = 90°), a 20% increase of the bolometric albedo is observed near perihelion. Heliocentric variations of the dust color are not significant in the analyzed time period. Measured color temperatures are varying from 260 to 320 K, and follow a r^0.6 variation in the r_h = 1.24-1.5 AU range, close to the expected r_h^0.5 value.
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