Probing Formation from Stars to Planets: Accretion, Binarity and Disks in Young Brown Dwarfs

在过去的15年里，太阳系外行星的发现是天文学史上最重要的进步之一。到目前为止，已经发现了300多个，在过多的恒星系统结构中，小到几个地球质量。确定这些行星的形成机制、性质和可居住性（以及未来几年将被探测到的低质量行星）是当前天体物理学研究的前沿。这些问题反过来又与星星形成的基本问题密切相关，因为行星是由吸积盘形成的，而吸积盘是恒星形成过程的一个不可分割的结果，并最终决定了恒星的最终质量。最后，恒星和行星的形成和性质与褐矮星密切相关：亚恒星体跨越恒星和行星之间的质量范围，并与两者共享许多特征。在这个项目中，我通过解决3个广泛的问题来研究恒星，棕矮星和行星的相互关联的起源：1）年轻的恒星和棕矮星如何从周围的吸积盘中吸积物质？2)褐矮星是如何形成的？3)行星能在褐矮星周围形成吗？这项研究需要各种观测技术，从高分辨率光谱学和分光偏振测量到自适应光学的分辨成像，部署在从光学到亚毫米的波长范围内，使用地面和空间设施，结合理论分析和数值建模。该项目的结果应能广泛而全面地说明从恒星到行星质量的物体形成的物理过程。

The discovery of extrasolar planets over the last decade and a half ranks among the most important advances in the history of astronomy. More than three hundred have been found so far, in a plethora of stellar system architectures, and down to a few Earth masses. Determining the formation mechanism, properties and habitability of these planets (and those of lower mass bound to be detected in coming years) is at the cutting edge of current astrophysical research. These questions are in turn intimately linked to the fundamental issue of star formation, since planets form out of the accretion disks that are an integral outcome of the star-formation process and that ultimately determine the final stellar mass. Finally, the formation and properties of both stars and planets are closely tied to those of brown dwarfs: substellar bodies that straddle the mass range between stars and planets and share many features with both. In this project, I investigate the inter-linked origins of stars, brown dwarfs and planets by addressing 3 broad questions: 1) How do young stars and brown dwarfs accrete material from their surrounding accretion disks? 2) How do brown dwarfs form? 3) Can planets form around brown dwarfs? The research entails a variety of observational techniques, from high-resolution spectroscopy and spectropolarimetry to resolved imaging with adaptive optics, deployed over wavelengths ranging from the optical to sub-millimetre and using both ground- and space-based facilities, allied with theoretical analysis and numerical modeling. The results of the project should provide a broad and comprehensive picture of the physical processes that underlie the formation of objects all the way from from stellar down to planetary masses.