A calculated methane line list for characterizing exoplanets and brown dwarfs

400多颗围绕其他恒星运行的恒星的发现开启了天文学的一个全新领域。天文学家现在开始对这些新世界提出疑问：它们是什么样子的？它们是什么做的？当然，有没有生命的迹象？描述这些被称为系外行星的行星需要使用新颖的观测技术，因为很难将这颗行星与其附近非常明亮的母星分开。据透露，到目前为止，从地球上观察到的行星中，大约有70颗从它们的恒星前面经过。对恒星在不同颜色光线下的轻微暗淡的观察，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行星母星的光相互作用。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是无法获得的；尤其是对于最常被观测到的系外行星“热木星”来说，这是一种围绕其母恒星附近运行的气态巨行星。对棕矮星和冷星的类似研究也是如此。在所有这些工作中，最明显的遗漏是关于甲烷的可靠数据。在系外行星中检测到了甲烷，它是棕矮星和冷碳星中的主要大气物种。然而，由于缺乏甲烷的实验室数据，这些天体和其他天文天体的模型受到了阻碍。甲烷这样的分子是如何吸收和发射光的，这是非常复杂的，因为特别是在高温下，它需要了解可能数十亿条单独的过渡线的位置和强度。这项提议将使用第一性原理量子力学计算，以提供一个全面和可靠的甲烷旋转振动线表。这些计算将与有限得多的对该问题的实验室研究进行比较，如有必要，将使用实验室研究来帮助提高所得到的计算线列表的准确性。新的线表将允许天文学家和其他科学家模拟甲烷如何吸收或发射光作为温度的函数。通过一个新的门户网站www.exomol.com，并使用其他基于网络的分发方法，将广泛提供该线路列表。

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.