用AKARI观测的C/2007 N3（Lulin）彗星2.5- 5微米光谱中母体H2O和CO2分子的探测
Detection of parent H2O and CO2 molecules in the 2.5--5 micron spectrum of comet C/2007 N3 (Lulin) observed with AKARI
摘要：
彗星C/2007 N3（鹿林）是由日本的红外卫星AKARI在近红外线观测的，其近日点后的日心距离为1.7天文单位。分别于2009年3月30日和2009年3月31日使用光谱（2.5--5.0微米）和成像（2.4、3.2和4.1微米）模式进行了观察。AKARI的彗星图像显示出一个向阳的新月状彗发和一个向反太阳方向延伸的尘埃尾巴。4.1微米图像（CO/CO2和尘埃颗粒）显示了与2.4和3.2微米图像（H2O和尘埃颗粒）不同的分布。观察到的光谱在2.66和4.26微米处显示出明显的条带，分别归因于H2O和CO2。这是第五颗在近红外光谱中直接探测到二氧化碳的彗星。此外，在AKARI光谱中检测到4.67微米处的CO和来自C-H轴承分子的宽3.2- 3.6微米发射带。由分子生成率计算出的CO_2/H_2 O和CO/H_2 O的相对丰度比分别为\sim 4%~ 5%和<2%。鹿林彗星是迄今为止观测到的彗星中CO和CO2丰度相对较低的彗星。
英文摘要：
Comet C/2007 N3 (Lulin) was observed with the Japanese infrared satellite AKARI in the near-infrared at a post-perihelion heliocentric distance of 1.7 AU. Observations were performed with the spectroscopic (2.5--5.0 micron) and imaging (2.4, 3.2, and 4.1 micron) modes on 2009 March 30 and 31 UT, respectively. AKARI images of the comet exhibit a sunward crescent-like shape coma and a dust tail extended toward the anti-solar direction. The 4.1 micron image (CO/CO2 and dust grains) shows a distribution different from the 2.4 and 3.2 micron images (H2O and dust grains). The observed spectrum shows distinct bands at 2.66 and 4.26 micron, attributed to H2O and CO2, respectively. This is the fifth comet in which CO2 has been directly detected in the near-infrared spectrum. In addition, CO at 4.67 micron and a broad 3.2--3.6 micron emission band from C-H bearing molecules were detected in the AKARI spectrum. The relative abundance ratios CO2/H2O and CO/H2O derived from the molecular production rates are \sim 4%--5% and < 2%, respectively. Comet Lulin belongs to the group that has relatively low abundances of CO and CO2 among the comets observed ever.
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