Star Formation: Following the Evolutionary Sequence from Cloud Assembly through Protostars and Circumstellar Disks

我们银河系的大部分恒星形成都发生在巨型分子云中。最简单地说，恒星的形成是局部引力塌缩的结果，由此产生的恒星-盘状系统的性质取决于气藏的数量和分布，以及运动学和角动量。然而，对分子云的观测揭示了一个动态环境，有大规模的超音速流动，显著的剪切，以及超音速湍流的证据。云中密度较高的气体与正在进行的恒星形成的位置相关，显示出一种更有序的结构，从容纳密集团块和核心的丝状网络开始。这些细丝中的一些可能表示激波前沿界面，另一些可能直接与云中的引力流入有关。事实上，分子云中结构的形成是由于重力和大规模超音速(湍流)运动之间的竞争。磁场调解也可能发挥重要作用。这项发现拨款将使人们能够研究物质、能量和动量在分子云中的流动和随时间的变化。 为了确定末态--一颗拥有行星系统的年轻恒星--有必要了解质量和角动量是如何从稠密的新生星云核心向下扩散的。这种致密的云核必须与更大的分子云，特别是内部丝状结构的网络结构的关系进行研究。最后，云中的形态和运动学，包括丝状结构，与分子云本身的形成和演化有关。让事情变得复杂的是，必须考虑几个反馈回路，最关键的是来自形成恒星本身的喷流和风的能量和动量。 我的研究生团队将通过观测被激发的一氧化碳来研究超音速(湍流)激波的重要性，在理论上计算出预期的能量耗散率。我们将继续积极研究云中的致密气体结构，途径包括：恒星形成模式的理论工作；恒星前核心引力稳定性的观测确定；以及将观测到的核心稳定范围和演化状态与模拟进行比较。此外，我们还将通过ALMA的观测，支持对原恒星质量组装的可能性进行直接调查。 这项发现拨款将使我的团队能够继续在恒星形成领域发挥领导作用，利用最近对分子云的大型调查(JCMT，Herschel，Spitzer)，新仪器前所未有的灵敏度和角度分辨率(ALMA，JWST)，以及当前和预期的数值模拟中可用的细节水平。

The bulk of the star formation in our Galaxy takes place within giant molecular clouds. At its simplest, the formation of a star is the result of localized gravitational collapse and the properties of the resulting star-disk system are dependent on the amount and distribution of the gas reservoir, along with its kinematics and angular momentum. Observations of molecular clouds, however, reveal a dynamic environment with large-scale supersonic flows, significant shear, and evidence for supersonic turbulence. The denser gases within the clouds, which correlate with the locations of on-going star formation, show a more ordered structure, beginning with a network of filaments housing dense clumps and cores. Some of these filaments may denote shock front interfaces and others may relate directly to the gravitational infall within the cloud. Indeed, it is expected that the formation of structure within a molecular cloud is due to the competition between gravity and large-scale supersonic (turbulent) motion. Magnetic field mediation may also play an important role. This Discovery Grant will enable research on the flow of mass, energy, and momentum through molecular clouds and over time. In order to determine the end-state - a young star with a planetary system - it is necessary to understand how mass and angular momentum funnel down from the dense natal cloud core. This dense cloud core must be investigated in relationship to the larger molecular cloud, and especially to the network of internal filamentary structure. Finally, the morphology and kinematics within the cloud, including the filamentary structure, relate to the formation and evolution of the molecular cloud itself. To complicate matters, several feedback loops must be taken into account, most critically the energy and momentum of jets and winds from the forming stars themselves.  My graduate student team will investigate the importance of supersonic (turbulent) shocks through observations of excited carbon monoxide, following theoretical calculations of the expected energy dissipation rate. We will continue to actively investigate dense gas structures within clouds through: theoretical work on the modes of star formation; observational determinations of gravitational stability in pre-stellar cores; and comparison of the observed stability range and evolutionary state of cores against simulations. Additionally, we will champion direct investigations into the possibility of proto-star mass assembly via episodic bursts, through ALMA observations.  This Discovery Grant will enable my team to continue its leadership role in the field of star formation, taking advantage of the recent large surveys of molecular clouds (JCMT, Herschel, Spitzer), the unprecedented sensitivity and angular resolution of new instrumentation (ALMA, JWST), and the level of detail available in current and anticipated numerical simulations.