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

我将利用这笔奖学金来探索，并最终了解辐射如何影响褐矮星的大气。褐矮星是恒星和系外行星之间缺失的一环。它们的大小与木星相当，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缩而形成的。第一颗棕矮星是在1995年拍摄的，同年也是第一颗系外行星被发现的一年，到目前为止，已经发现了1200多颗棕矮星。离我们最近的褐矮星是太阳的第四近邻！年轻的棕矮星与直接成像的系外行星有着非常相似的大气层，棕矮星经常被用来告诉我们在系外行星的大气层中我们会看到什么。然而，大多数系外行星的轨道离它们的主星非常近，主星要亮得多，这使得很难确定其大气中有什么。我将研究那些与热伴星在非常近的轨道上运行的褐矮星。在这些系统中，褐矮星可以在短短2小时内完成一个轨道。这些系统是潮汐锁定的，这意味着褐矮星的同一侧一直面对着伴星。我发现，这颗褐矮星的热面比暗面要热500度，导致风将能量从热面输送到冷面。很明显，加热褐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。我将在世界各地用4米和8米的望远镜观察这些双星。我的观测将监视这颗褐矮星围绕它的伴星运行，以了解当褐矮星加热的一面进入我们的视野时，它会变得多亮。通过观察不同的波长，我将能够看到大气中不同的层对加热的反应。我也会在褐矮星轨道上的不同位置取它的光谱。2018年发射的新型詹姆斯·韦伯太空望远镜是这项工作的理想设备。我将利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褐矮星伴星的温度，因此研究尽可能多的系统，以及不同温度的主星是非常重要的。然而，到目前为止，已知的这些系统很少，所以在研究已知系统的同时，我将通过一项新的调查来发现新的系外行星，NGTS，以及广泛的田野调查。这些巡天以多种波长对天空进行成像，通过结合这些数据，我将能够识别出新的双星。然后，我将用世界上最先进的望远镜对它们进行更多的观测，以测量它们的质量和轨道时间尺度。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褐矮星被加热时大气中发生的过程，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.