Uncovering the Episodic Nature of Star Formation and Revealing the Environment in which Stars and Planets Form

恒星的形成和它的行星系是紧密相连的。当分子云中的局部区域变得引力不稳定时，恒星的形成就开始了，原恒星及其周围的原行星盘的自由落体积聚取决于气藏的分布及其相关的运动学和自旋。理论计算表明，大部分原恒星质量首先到达磁盘，主要由角动量和磁场调节，然后必须通过磁盘吸积机制到达原恒星。行星是在星周圆盘内形成的，最近的观测提供了带环和间隙的圆盘的壮观图像——进一步证明了行星形成在恒星生命的早期是普遍存在的和活跃的。在我的国际研究团队在过去四年中使用JCMT和ALMA进行的开创性观测工作的基础上，我和我的研究生将以每月的时间尺度监测100多个深嵌（非常年轻的）原恒星的亚毫米变化，以便可靠地确定它们的质量聚集的幕式性质。这些最年轻的原恒星主要通过原恒星吸积盘释放的能量辐射。这种辐射的大部分是在远红外和亚毫米波长观测到的，这是由于被包裹的外壳中的尘埃对星光进行了再处理。因此，监测亚毫米变异性提供了对系统潜在吸积历史的直接测量。我们已经发现许多原恒星是可变的，并发现了一个周期为18个月的可变原恒星（可能是由伴星或行星触发的）。因此，将这些观测延长到整整十年，将提供一个足够大的样本，以便对吸积变化的频率、幅度和持续时间进行可靠的统计确定，并分析单个原恒星变化的物理/化学条件。作为一个整体，这些测量直接关系到吸积不稳定性的类型和它们的盘的位置。因此，它们为理论盘吸积假设提供了关键的约束，并为行星形成模型提供了信息。恒星形成研究的一个关键目标是确定原恒星系统形成的方式，以便了解恒星的初始质量函数、恒星的多样性、行星系统的形成，以及可能的生命起源。我们最近在多年的时间尺度上成功地监测了深嵌的原恒星，为确定嵌入的原恒星的质量集合和内部原行星盘中的吸积物理提供了一种独特的方法。因此，未来的仪器，如CCAT-p， CMB S-4， SPICA, Origins，预计将在关键科学项目中使用我们的时域技术。

The formation of a star and its planetary system are intimately coupled. Star formation commences when a localized region within a molecular cloud becomes gravitationally unstable, with the free-fall build-up of the protostar and its surrounding protoplanetary disk depending on both the distribution of the gas reservoir and its associated kinematics and spin. Theoretical calculations suggest that the majority of the protostellar mass arrives first onto the disk, predominantly mediated by angular momentum and magnetic fields, and must then reach the protostar via disk accretion mechanisms. It is within the circumstellar disk that planets are expected to form, and recent observations have provided spectacular images of disks with rings and gaps- furthering the suggestion that planet formation is both ubiquitous and active early in the lifetime of stars. Building on the pioneering observational work that my international research team has performed over the last four years using the JCMT and ALMA, my graduate students and I will monitor the submillimetre variability from more than one hundred deeply embedded (very young) protostars on monthly timescales in order to robustly determine the episodic nature of their mass assembly. These youngest protostars radiate primarily through the energy released during protostellar accretion from the disk. The bulk of this radiation is observed at far infrared and submillimetre wavelengths due to reprocessing of the starlight by dust in the enshrouding envelope. Thus, monitoring the submillimetre variability provides a direct measure of the underlying accretion history of the system. Already, we have revealed that many protostars are variable and uncovered an eighteen month periodic variable protostar (likely triggered due to a companion star or planet). Extending these observations over a full decade will therefore provide a large enough sample to enable robust statistical determinations of the frequency, amplitude, and duration of accretion variability and an analysis of the physical/chemical conditions under which individual protostars vary. As a whole, these measurements relate directly to the type(s) of accretion instability involved and their disk location(s). They therefore provide critical constraints on theoretical disk accretion hypotheses and inform planet formation models. A key goal of star formation studies is to determine the manner in which protostellar systems form, in order to understand the stellar initial mass function, stellar multiplicity, the formation of planetary systems, and possibly the origins of life. Our recent successful monitoring of deeply embedded protostars over multi-year timescales has provided a unique approach to determining the mass assembly of embedded protostars and the accretion physics within the inner protoplanetary disk. Thus, future instruments, e.g. CCAT-p, CMB S-4, SPICA, Origins, are anticipating using our time-domain techniques for key science projects.