The Planet-Disk Connection: Accretion, Disk Structure, and Planet Formation

“恒星和行星系统是如何发展的？生命是我们这个星球所独有的吗？”是人类面临的重大问题之一，也是STFC提出的科学挑战之一。在邓迪，我们是一个小而年轻而充满活力的部门，专注于理解恒星和行星的形成，该小组在苏格兰大学物理联盟（SUPA）和圣安德鲁斯系外行星中心的更大背景下不断发展。我们的主要目标是通过观测和计算来探索行星的形成环境。行星诞生于年轻恒星周围形成的原行星盘，由气体和尘埃组成，大小从非常小的颗粒到鹅卵石。我们使用多望远镜，多波长数据和最先进的计算机模拟来跟踪恒星与原行星盘的形成，跟踪磁盘在它们分散时的演变，并研究行星系统如何从耗散磁盘形成和演化。观测研究正在进行的行星形成的主要问题之一是，最里面的部分（包括宜居带，液态水可以使行星拥有生命的区域）太小太暗，即使是最强大的现有干涉仪也无法直接解决。我们的项目将开发特殊的观测技术，以探索年轻恒星周围和靠近中心恒星的最内层行星形成区域的条件，在那里许多行星正在被发现。由于对磁盘的观测提供了磁盘演化的快照，而观测到的系外行星显示了行星形成的最终状态，我们还旨在通过使用计算机模拟来连接行星形成的开始和结束（即磁盘和行星），并将模拟与观测到的磁盘和系外行星进行比较。第一个关键是探索速度和时间维度，以跟踪微小的空间结构：利用多普勒效应和随着时间的推移的重复观测，我们可以跟踪磁盘物质，因为它的轨道，螺旋和吸积到中心恒星，绘制最内层区域在几个恒星半径和确定整个磁盘的物质流动。这两个量对于探索恒星在未来是否会足够安静以允许适宜居住的行星，以及物质在行星形成区的圆盘中移动的方式都非常重要。它还将使我们能够将观测到的行星特征与吸积和活动特征区分开来，从而促进未来对非常年轻的行星的探测。第二个关键是“罗塞塔石”技术，使用不同的望远镜在许多不同的波长（颜色）进行观测。类似于原始罗塞塔石碑的不同语言，每个波长以略微不同的方式告诉我们圆盘的各个方面。通过对大量天体的综合研究，我们可以获得原行星盘整体特性的精确图像，并探索行星形成的特征。第三个关键是利用计算机模拟，通过在几百万年的时间尺度上探索行星的形成，弥合原行星盘和系外行星系统之间的差距。我们将从我们对大量磁盘的多波长观测中构建一个现实的磁盘模型，并将其作为行星形成模拟的起点。然后，我们将把模拟行星系统的特性与观测到的行星系统的特性进行比较，这也将帮助我们排除或确认无法直接观测到的磁盘特性和物理过程。我们的目标是通过揭示行星起源于哪种类型的盘来了解已知的行星种类，并通过探索行星形成对盘演化的影响来理解观测到的原行星盘的种类。

"How do stars and planetary systems develop and is life exclusive to our planet?" is one of the major questions of humanity, and also one of the Science Challenges proposed by the STFC. In Dundee, we are a small but young and vibrant department with a strong focus in understanding the formation of stars and planets, and the group is growing within the larger context of the Scottish Universities Physics Alliance (SUPA) and the St Andrews Exoplanet Centre.Our main objective is to explore planet formation environments both observationally and computationally. Planets are born in protoplanetary disks formed around young stars, composed of gas and dust with sizes from very small particles to pebbles. We use multi-telescope, multi-wavelength data and a state-of-the-art computer simulations to track the formation of stars together with protoplanetary disks, to follow the evolution of disks as they disperse, and to study how planetary systems form and evolve out of a dissipating disk. One of the main problems of observationally studying the ongoing planet formation in disks is that the innermost part (which includes the habitable zone, the region where liquid water could enable planets to host life) is too small and too faint to be directly resolved even by the most powerful existing interferometers. Our project will develop special observational techniques to explore the conditions around young stars and in the innermost planet formation regions near the central stars, where many planets are now being discovered. Since observations of disks provide snapshots of disk evolution while observed exoplanets show the end state of planet formation, we also aim to connect the beginning and the end of planet formation (i.e. disks and planets) by using computer simulations, and will compare simulations with both observed disks and exoplanets. The first key is to explore the velocity and time dimension to track tiny spatial structures: using the Doppler effect and repeated observations over time, we can track the disk material as it orbits, spirals and accretes onto the central star, mapping the innermost regions at few stellar radii and determining the flow of matter throughout the disk. Both quantities are very important to explore whether the star will be quiescent enough in the future to allow for habitable planets, and the way matter moves through the disk in the planet-forming zone. It will also enable us to distinguish observational planetary signatures from those of accretion and activity and thus facilitate the detection of very young planets in the future. The second key is the "Rosseta Stone" technique, using observations at many different wavelengths (colours), taken with various telescopes. Similar to the different languages of the original Rosetta Stone, each wavelength tells us about aspects of the disk in a slightly different way. By combining them all for large numbers of objects, we can obtain an accurate picture of the global properties of protoplanetary disks and explore the signatures of planet formation. The third key is to use computer simulations to bridge the gap between protoplanetary disks and exoplanetary systems by exploring the formation of planets over a few million year timescale. We will construct a realistic disk model from our multi-wavelength observations for a large number of disks and use that as the starting point of planet formation simulations. We will then compare the properties of the simulated planetary systems with those of observed ones, which will also help us to rule out or confirm disk properties and physical processes that are not directly observable. Our goals are to put into context the known variety of planets by revealing from which kinds of disks they have originated, and to understand the observed variety of protoplanetary disks by exploring the effect of planet formation on the evolution of the disk.