Irradiated atmospheres of brown dwarfs: providing an insight into exoplanet atmospheres

我将利用这项研究来探索，并最终了解辐射如何影响棕矮星的大气。棕矮星是恒星和系外行星之间缺失的一环。它们的大小和木星差不多，但质量可能是木星的70倍。然而，与系外行星不同的是，它们像恒星一样，是由巨大的气体云坍塌形成的。第一颗棕矮星是在1995年拍摄的，也就是第一颗系外行星被发现的同一年，到目前为止已经发现了1200多颗。距离我们最近的褐矮星是太阳第四近的邻居！年轻的棕矮星的大气层与直接拍摄到的系外行星非常相似，而且棕矮星经常被用来告诉我们在系外行星大气中我们会看到什么。然而，大多数系外行星的轨道都离它们的主星很近，而主星要明亮得多，因此很难确定它的大气层中有什么。我将研究与热伴星在非常近的轨道上的棕矮星。在这些系统中，棕矮星可能在短短2小时内完成一次轨道运行。这些系统是潮汐锁定的，这意味着棕矮星的同一侧不断面对同伴。我发现，这一热面比棕矮星的暗面温度高达500度，导致风将能量从热面输送到冷面。很明显，加热棕矮星或系外行星会极大地改变其大气，因为辐射会分裂并产生新的分子。我将使用世界各地的400万和800万望远镜来观察这些双星。我的观测将监测这颗棕矮星围绕它的同伴运行，以了解当它被加热的一面进入视野时，这颗棕矮星会变得多么明亮。通过观察不同的波长，我将能够看到大气中的不同层对加热的反应。我还将拍摄这颗棕矮星轨道上不同位置的光谱。2018年发射的新的詹姆斯·韦伯太空望远镜是进行这项工作的理想设施。我将使用这些光谱来确定大气是由什么组成的，以及哪些分子是由辐射产生的。新分子的产生在很大程度上取决于棕矮星的伴星有多热，所以研究尽可能多的系统，与不同温度的宿主恒星合作是非常重要的。然而，到目前为止，这些系统中已知的很少，所以除了研究已知的系统外，我还将利用一项发现系外行星的新调查，即NGTS，以及广泛的实地考察来发现新的系统。这些测量在许多波长上对天空进行成像，通过结合它们的数据，我将能够识别新的双星。然后，我将用世界领先的望远镜对它们进行更多的观测，以测量质量和轨道时间刻度。最后，我将与我的合作者一起创建这些系统的模型。这些模型将被用来解释棕矮星大气在被加热时发生的过程，也将被用来解释在被加热的系外行星大气中发生的事情。

I will use this fellowship to explore, and ultimately understand how irradiation affects the atmospheres of brown dwarfs. Brown dwarfs are the missing link between stars and exoplanets. They are the size of Jupiter but may be up to 70 times as massive. However, unlike exoplanets, they form like stars, from the collapse of a massive gas cloud. The first brown dwarf was imaged in 1995, the very same year as the first exoplanet detection, and to date over 1200 have been discovered. Our closest brown dwarf is the Sun's fourth nearest neighbour! Young brown dwarfs have very similar atmospheres to directly imaged exoplanets, and brown dwarfs are often used to tell us what we would expect to see in an exoplanet atmosphere. However, most exoplanets are orbiting very close to their host star, which is much brighter, making it very difficult to determine what is in its atmosphere. I will study brown dwarfs that are in very close orbits with a hot companion. In these systems, the brown dwarf may complete an orbit in as little as 2 hours. These systems are tidally locked, meaning that the same side of the brown dwarf continually faces the companion. I discovered that this hot side can be up to 500 degrees hotter than the dark side of the brown dwarf, causing winds that transport energy from the hot side to the cold side. It is clear that heating a brown dwarf or exoplanet drastically alters its atmosphere, as the irradiation splits up and creates new molecules. I will observe these binaries using 4m and 8m telescopes around the world. My observations will monitor the brown dwarf as it orbits its companion, to understand how much brighter the brown dwarf gets as its heated side moves into view. By observing in different wavelengths, I will be able to see how the different layers in the atmosphere respond to the heating. I will also take spectra of the brown dwarf at different points in its orbit. The new James Webb Space Telescope, launched in 2018 is an ideal facility for this work. I will use these spectra to determine what the atmosphere is made of, and which molecules are being created by the irradiation. The creation of new molecules depends very much on how hot the brown dwarf's companion is, so studying as many systems as possible, with host stars of different temperatures is very important. There are, however, very few of these systems known to date, so as well as studying the known systems, I will discover new ones using a new survey for discovering exoplanets, NGTS, and also wide field surveys. These surveys image the sky at many wavelengths, and by combining data from them I will be able to identify new binaries. I will then obtain more observations of them with world leading telescopes, to measure the masses, and the orbital timescale. Finally I will work with my collaborators to create models of these systems. These models will be used to explain the processes occurring in the brown dwarf atmosphere as it is heated and will also be used to explain what happens in heated exoplanet atmospheres.