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

揭示恒星形成的情景性质并揭示恒星和行星形成的环境

• 批准号: RGPIN-2020-03928
• 负责人: Johnstone, Douglas
• 金额: $ 2.99万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763015
• 关键词: Uncovering; Episodic; Nature; Star; Formation

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.

恒星的形成和它的行星系统是紧密耦合的。当分子云中的局部区域变得重力不稳定时，恒星的形成就开始了，原恒星及其周围的原行星盘自由落体的积累取决于气藏的分布及其相关的运动学和自转。理论计算表明，大部分原恒星质量首先到达圆盘，主要是通过角动量和磁场的调节，然后必须通过圆盘吸积机制到达原恒星。行星预计会在行星盘内形成，最近的观测提供了带有环和缝隙的盘的壮观图像-进一步表明，行星形成在恒星生命早期是普遍存在和活跃的。在我的国际研究团队在过去四年里使用JCMT和ALMA进行的开创性观测工作的基础上，我的研究生和我将在每月的时间尺度上监测100多颗深度嵌入的(非常年轻的)原恒星的亚毫米变率，以便有力地确定它们大规模聚集的插曲性质。这些最年轻的原恒星主要通过原恒星吸积过程中从盘面释放的能量来辐射。这种辐射的大部分是在远红外和亚毫米波长下观察到的，这是由于覆盖层中的尘埃对星光进行了再处理。因此，监测亚毫米级的可变性提供了系统潜在的吸积历史的直接测量。我们已经揭示了许多原恒星是可变的，并发现了一个18个月周期可变的原恒星(很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足够大的样本，从而能够对吸积变化的频率、幅度和持续时间进行强有力的统计确定，并分析单个原恒星变化的物理/化学条件。总体而言，这些测量结果与所涉及的吸积不稳定类型(S)及其盘位置(S)直接相关。因此，它们为理论上的盘吸积假说提供了关键的约束，并提供了行星形成模型。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，以便了解恒星初始质量函数、恒星多样性、行星系统的形成，以及可能的生命起源。我们最近在多年时间尺度上对深埋原恒星的成功监测提供了一种独特的方法来确定嵌入的原恒星的质量组装和内原行星盘内的吸积物理。因此，未来的仪器，如CCAT-p、CMB S-4、Spica、Origins，都有望在关键科学项目中使用我们的时域技术。