用斯皮策Space Telescope对彗星CO2、CO和微粒排放的调查：彗星的烟雾检查
Survey of cometary CO2, CO, and particulate emissions using the Spitzer Space Telescope: Smog check for comets
摘要：
我们使用斯皮策太空望远镜上的红外线阵列相机在以3.6和4.5微米为中心的宽滤光片中测量了23颗彗星。在3.6微米的过滤器中，辐射来自于被尘埃颗粒散射的太阳光;这些图像通常在核附近有一个慧差，在反太阳方向有一个尾巴，这是由于尘埃颗粒被太阳辐射压力扫回。4.5微米过滤器包含相同的尘埃颗粒，以及来自CO2和CO气体的强发射谱线;这些显示出不同的形态，在这种情况下，我们推断它们以气体为主。根据4.5到3.6微米亮度的比值，我们将调查彗星分为“富”和“贫”的CO2+CO。“这种分类与A 'Hearn之前基于碳链分子丰度的分类相关，从某种意义上说，被归类为碳链分子“耗尽”的彗星的CO2+ CO含量也“贫乏”。IRAC 4.5微米图像的特征是形态光滑，典型地，在向阳半球中的扇形体，其径向轮廓近似地随着距核的投影距离的倒数而变化，这将适用于恒定的生产和自由膨胀。许多彗星的径向和方位角都有非常显著的增强，这些增强在气体和尘埃之间往往是不同的，这表明固体物质的喷射可能是由H2O或CO2驱动的。图像中的显著特征包括以下内容。103 P/哈特利2号有一个突出的气体排放环，可能是由于斯皮策图像之前的CO2爆发。在88 P/Howell的图像中出现了明显的双喷流。一个突出的单一喷流是明显的3颗彗星。螺旋在29 P和C/2006 W3中很明显;我们测量了后者彗星的21小时旋转速率。在10 P/Tempel 2和2 P/Encke的图像中，弧形（可能是螺旋的一部分）很明显。
英文摘要：
We surveyed 23 comets using the Infrared Array Camera on the Spitzer Space Telescope in wide filters centered at 3.6 and 4.5 microns. Emission in the 3.6 micron filter arises from sunlight scattered by dust grains; these images generally have a coma near the nucleus and a tail in the antisolar direction due to dust grains swept back by solar radiation pressure. The 4.5 micron filter contains the same dust grains, as well as strong emission lines from CO2 and CO gas; these show distinct morphologies, in which cases we infer they are dominated by gas. Based on the ratio of 4.5 to 3.6 micron brightness, we classify the survey comets as CO2+CO "rich" and "poor." This classification is correlated with previous classifications by A'Hearn based on carbon-chain molecule abundance, in the sense that comets classified as "depleted" in carbon-chain molecules are also "poor" in CO2+CO. The gas emission in the IRAC 4.5 micron images is characterized by a smooth morphology, typically a fan in the sunward hemisphere with a radial profile that varies approximately as the inverse of projected distance from the nucleus, as would apply for constant production and free expansion. There are very significant radial and azimuthal enhancements in many of the comets, and these are often distinct between the gas and dust, indicating that ejection of solid material may be driven either by H2O or CO2. Notable features in the images include the following. There is a prominent loop of gas emission from 103P/Hartley 2, possible due to an outburst of CO2 before the Spitzer image. Prominent, double jets are present in the image of 88P/Howell. A prominent single jet is evident for 3 comets. Spirals are apparent in 29P and C/2006 W3; we measure a rotation rate of 21 hr for the latter comet. Arcs (possibly parts of a spiral) are apparent in the images of 10P/Tempel 2, and 2P/Encke.
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