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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=739569
• 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.

一颗星星的形成和它的行星系统是紧密相连的。当分子云内的局部区域变得引力不稳定时，星星就开始形成，原星星及其周围原行星盘的自由落体式堆积取决于气体储存器的分布及其相关的运动学和自旋。理论计算表明，大部分的原恒星质量首先到达磁盘上，主要是通过角动量和磁场介导的，然后必须通过磁盘吸积机制到达原恒星。行星预计会在拱星盘内形成，最近的观测提供了具有环和间隙的圆盘的壮观图像-进一步表明行星形成在恒星生命早期普遍存在且活跃。 基于我的国际研究团队在过去四年中使用JCMT和阿尔马进行的开创性观测工作，我和我的研究生将在每月的时间尺度上监测100多颗深埋（非常年轻）原恒星的亚毫米变化，以确定其质量组装的偶发性质。这些最年轻的原恒星主要通过原恒星吸积过程中释放的能量辐射。大部分的辐射是在远红外和亚毫米波长下观察到的，这是由于星光被包围的信封中的尘埃再处理。因此，监测亚毫米的变化提供了一个系统的基本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个月周期可变的原星星（可能是由于伴星星星或行星引发的）。因此，将这些观测扩展到整整十年，将提供足够大的样本，以便对吸积变化的频率、幅度和持续时间进行可靠的统计测定，并分析单个原恒星变化的物理/化学条件。总的来说，这些测量直接关系到所涉及的吸积不稳定性的类型及其盘的位置。因此，他们提供了关键的限制理论磁盘吸积假说和通知行星形成模型。星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。我们最近成功地监测深嵌入的原恒星在多年的时间尺度提供了一个独特的方法来确定嵌入的原恒星的质量组装和吸积物理内部原行星盘。因此，未来的仪器，如CCAT-p，CMB S-4，SPICA，起源，预计将使用我们的时域技术的关键科学项目。