RUI: The Evolution of Sun-like Stars Through Their Mass Accreting Phase

RUI：类太阳恒星通过质量吸积阶段的演化

• 批准号: 0071063
• 负责人: Edwin Ladd
• 金额: $ 7.73万
• 依托单位: Bucknell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-01 至 2004-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0071063&HistoricalAwards=false
• 关键词: RUI; Evolution; Sun; like; Stars

AST-0071063LADDIt is abundantly clear that stars must form from the aggregation of diffuse interstellar material. However, how this process occurs, and specifically which mechanisms play a dominant role in the evolution, are still poorly understood. Stars in the process of formation do not accrete all of the material energetically available to them, but instead reject some fraction of their surrounding dense cores during the formation process. While the rejection process is not well understood, it is suspected that jets and bipolar outflows from the forming star play a major role.The goal of this research program is to understand the time evolution of stars and their placental cores during the critical phase when the mass of a forming star is determined. This phase is dominated by the gravitational infall of material from the core onto the star, and the ballistic ejection of material from the immediate vicinity of the star in the form of bipolar jets and outflows. Both processes have substantial impacts on the core - the former removes mass, while the latter injects energy. The complicated interplay between these two processes strongly affects the evolution of the core, and, since the core is the mass reservoir out of which the star will form, may even set the star's final mass. While the mass of a forming star is impossible to measure directly, the mass of the circumstellar core can be inferred from observations of the rotational transitions of its molecular constituents. Furthermore, the energetics of the core material can be measured from the velocity structure of this spectral line emission. This research activity seeks to track the evolution of circumstellar core material through the main mass accreting phase of star formation, via studies of populations of forming stars.An initial study of sources in the Taurus molecular cloud indicates that the circumstel-lar core is emptied on about a hundred million year time scale, with the most rapid decrease taking place at the earliest times. The rate of mass loss from the circumstellar core is consistent with that expected from standard models of accreting protostars; except during these earliest phases when the mass loss rate is larger than that expected from these models.The analysis of the velocity structure of these cores suggests that bipolar outflows from the forming star couple to core material more efficiently during the earliest times, during which outflows may inject substantial energy into the core. In addition, maps of the spatial distribution of the "stirred-up" core material indicate that this interaction takes place in the inner core, near the forming star. This research program will apply the methodology proved for modeling core forming stars in the Taurus region to all very young stars in large complexes nearer than 350 parsec. The survey observations will be conducted such that the linear spatial resolution will be constant, producing a data set free of distance-dependent effects, and facilitating comparisons between star forming complexes. The new observations will build on the results from the Taurus survey by increasing the sample size by at least a factor of five, and will constrain models of the time-evolution of forming stars during the critical phase in which they accrete most of their mass.This project is funded by the Division of Astronomical Sciences.***

非常清楚的是，恒星必须由弥漫的星际物质聚集而成。 然而，这一过程是如何发生的，特别是哪些机制在进化中起主导作用，仍然知之甚少。 在形成过程中的恒星不会吸积所有的物质，而是在形成过程中排斥周围致密核心的一部分。虽然排斥过程还不是很清楚，但人们怀疑形成中星星的喷流和双极外流起了主要作用。这一研究计划的目标是了解恒星及其胎盘核心在临界阶段的时间演化，即确定形成中星星的质量。这一阶段主要是物质从核心到星星的引力下落，以及物质从星星附近以双极喷流和外流形式的弹道喷射。这两个过程都对地核产生重大影响--前者去除质量，而后者注入能量。这两个过程之间复杂的相互作用强烈地影响着核心的演化，而且，由于核心是星星形成的物质库，甚至可能决定星星的最终质量。虽然形成中的星星的质量无法直接测量，但星周核心的质量可以通过观察其分子组成的旋转跃迁来推断。此外，可以从该谱线发射的速度结构测量芯材料的能量。这项研究活动旨在通过研究正在形成的恒星的种群，追踪星周核心物质在星星形成的主要质量吸积阶段的演变情况，对金牛座分子云中来源的初步研究表明，星周核心在大约一亿年的时间尺度上是空的，最快的减少发生在最早的时候。星周核心的质量损失率与标准吸积原恒星模型所预期的一致;除了在这些最早的阶段，当质量损失率大于这些模型的预期。这些核心的速度结构的分析表明，双极流出的形成星星耦合到核心材料更有效地在最早的时候，在此期间，流出物可将大量能量注入堆芯。此外，“搅动”核心物质的空间分布图表明，这种相互作用发生在内核，靠近形成中的星星。这项研究计划将适用于模拟金牛座地区核心形成恒星的方法，以接近350秒差距的大型复合体中的所有非常年轻的恒星。巡天观测的进行将使线性空间分辨率保持不变，从而产生一组不受距离影响的数据，并便于对形成星星的复合体进行比较。新的观测将以金牛座巡天的结果为基础，将样本量至少增加五倍，并将限制形成中恒星在吸积大部分质量的关键阶段的时间演化模型。