A calculated methane line list for characterizing exoplanets and brown dwarfs

400多颗绕轨道运行的恒星的发现开辟了一个全新的天文学领域。天文学家现在开始对这些新世界提出疑问：它们是什么样的？它们是用什么做的？当然，有生命迹象吗？描述这些被称为系外行星的特征需要使用新的观测技术，因为几乎不可能将行星与其附近非常明亮的母恒星分开。从地球上看，迄今为止探测到的大约70颗行星从它们的恒星前面经过。对恒星轻微变暗的不同颜色的光的观察开始产生关于系外行星组成的有价值的信息。然而，为了理解这些观测结果，需要建立大气模型来模拟行星如何与来自其母星的光相互作用。这反过来又需要大量的实验室数据。然而，在许多情况下，所需的实验室数据往往根本无法获得；对于最常见的一类系外行星“热木星”来说尤其如此，热木星是一种气体巨行星，它们的轨道靠近母恒星。对棕矮星和低温恒星的类似研究也是如此。所有这些工作中最明显的遗漏是甲烷的可靠数据。甲烷在系外行星中被发现，是褐矮星和低温碳星的主要大气物质。然而，由于缺乏甲烷的实验室数据，这些天体和其他天体的模型受到了阻碍。像甲烷这样的分子是如何吸收和发射光的是非常复杂的，特别是在高温下，它需要了解可能数十亿个单独的过渡线的位置和强度。该方案将利用第一性原理量子力学计算为甲烷提供一个全面可靠的旋转振动线列表。这些计算结果将与有限得多的实验室研究结果进行比较，必要时将用于帮助提高计算得到的线表的准确性。新的清单将使天文学家和其他科学家能够模拟甲烷如何吸收或发射光作为温度的函数。这个行列表将通过一个新的web门户网站www.exomol.com和其他基于web的分发方法广泛提供。

The discovery of over 400 orbiting other stars has opened a whole new field of astronomy. Astronomers are now beginning to ask questions about these new worlds: what are they like? what are they made of? and of course, are there any signs of life? Characterizing these exoplanets, as they are called, requires the use novel observational techniques as it is rarely possible to separate the planet from its nearby and very bright parent star. It transpires that about 70 of the planets detected so far pass in front of their star when viewed from earth. Observation of the slight dimming of the star for different colours of light is beginning to yield valuable information on the composition of exoplanets. However to do understand these observations requires building atmospheric models to simulate how the planet interacts with the light coming from the planet's parent star. This is in turn requires huge quantities of laboratory data. However in many cases the laboratory data required is often simply not available; this is particularly true for the most commonly observed class of exoplanets 'hot Jupiters', which are gas giant planets who orbit close to their parent star. It is also true for similar studies of brown dwarfs and cool stars. The most glaring omission in all this work is reliable data for methane. Methane has been detected in exoplanets and is a major atmospheric species in brown dwarfs and cool carbon stars. However models of these and other astronomical objects are hampered by the lack of laboratory data on methane. How a molecule such as methane absorbs and emits light is very complicated since, particularly at elevated temperatures, it requires knowledge of the position and strength of probably many billions of individual transition lines. This proposal will use first principles quantum mechanical calculations to provide a comprehensive and reliable rotation-vibration line list for methane. These calculations will be compared with the much more limited available laboratory studies of the problem, which will if necessary be used to help improve the accuracy of the resulting computed line list. The new line list will allow astronomers and other scientists to model how methane absorbs or emits light as a function of temperature. This line list will be made widely available via a new web portal, www.exomol.com, and using other web-based distribution methods methods.