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

非常清楚的是，恒星一定是由漫射星际物质的聚集形成的。然而，这个过程是如何发生的，特别是哪些机制在进化中起主导作用，仍然知之甚少。恒星在形成过程中不会吸积所有能量上可用的物质，而是在形成过程中排斥周围致密核心的一部分。虽然排斥过程还没有被很好地理解，但人们怀疑形成恒星的射流和双极流出物起了主要作用。本研究计划的目的是了解恒星及其胎盘核在确定形成恒星质量的关键阶段的时间演化。这一阶段主要是物质从核心向恒星的引力下降，以及物质从恒星附近以双极喷流和流出形式的弹道抛射。这两个过程对核心都有很大的影响——前者减少质量，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，由于核心是恒星形成的质量储存库，甚至可能决定恒星的最终质量。虽然形成恒星的质量不可能直接测量，但可以通过观察其分子成分的旋转转变来推断星周核心的质量。此外，可以通过谱线发射的速度结构来测量核心物质的能量学。这项研究活动旨在通过研究形成恒星的数量，追踪恒星形成的主要质量吸积阶段的星周核心物质的演变。对金牛座分子云来源的初步研究表明，星周核心在大约1亿年的时间尺度上被清空，在最早的时候减少得最快。星周核心的质量损失率与吸积原恒星标准模型的预期一致；除了在这些早期阶段，质量损失率大于这些模型的预期。对这些核心的速度结构分析表明，形成恒星的双极流出物在早期更有效地耦合到核心物质，在此期间流出物可能向核心注入大量能量。此外，“被搅动”的核心物质的空间分布图表明，这种相互作用发生在靠近形成恒星的内核。这个研究项目将把在金牛座区域的核心形成恒星建模中证明的方法应用于所有在350秒差距以上的大型复星中非常年轻的恒星。在进行巡天观测时，线性空间分辨率将是恒定的，从而产生一个不受距离影响的数据集，并促进恒星形成复合体之间的比较。新的观测结果将建立在金牛座调查结果的基础上，将样本量增加至少五倍，并将限制形成恒星在吸积大部分质量的关键阶段的时间演化模型。该项目由天文科学学部资助

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.***