Final Mass Loss on the AGB and Planetary Nebula Formation

这个项目解决了普通(1到8个太阳质量)恒星从渐近巨星枝到行星状星云阶段的演化过程中一个重要的悬而未决的问题：最终质量损失的性质和它们的喷流的起源。赤道质量损失增强和高速喷流主导了行星状星云的早期发展，似乎几乎无处不在，但它们的起源尚不清楚。在这里，对恒星喷出的中性气体和尘埃的观测将被用来解决这一演化阶段的关键方面。1)AGB包层的几何形状：将在光学波长进行深度成像，以确定渐近巨型分支顶端的星周包络的结构。结果将被用来确定导致转变的质量损失几何的长期演变，这为可能的喷流触发机制提供了关键约束。2)喷流和赤道环：还将使用超高分辨率(约0.3角秒)毫米干涉术对原始/年轻行星星云中新形成的喷流和环状星云进行观测。分子气体的光谱成像将在12CO、13CO和其他分子物种的线条上进行，以确定喷流和环面的几何、质量和动力学以及它们之间的相互关系。观测将被用来提供一般的约束条件，并测试最终质量损失和喷流形成的特定情景。这些结果有望极大地提高我们对恒星演化这一关键阶段的理解。该项目将影响天体物理学的其他领域，因为行星星云构成了一类新的具有喷流的物体，其独特的特征可能为喷流如何形成提供新的见解。该项目还涉及纽约大学研究生和本科生的教育和研究培训。它进一步促进了国际科学合作，并为哈金斯教授正在进行的广泛以恒星演化为中心的外展工作奠定了基础。这包括“课程中的明星”，这是一个与教育专家和实习教师合作的项目，旨在加强纽约市公立学校的科学课程。

This project addresses an important unsolved problem in the evolution of ordinary (1 to 8 solar mass) stars in their transition from the asymptotic giant branch to the planetary nebulae phase: the nature of the final mass loss and the origin of their jets. Enhanced equatorial mass loss and high-velocity jets dominate the early development of planetary nebulae and appear to be nearly ubiquitous, but their origins are unknown. Here, observations of the neutral gas and dust ejected by the stars will be used to address key aspects of this evolutionary phase. 1) The Geometry of AGB Envelopes: Deep imaging will be carried out at optical wavelengths to determine the structure of circumstellar envelopes at the tip of the asymptotic giant branch. The results will be used to determine the long-term evolution of the mass loss geometry leading up to the transition, which provides key constraints on possible jet triggering mechanisms. 2) Jets and Equatorial Tori: Observations will also be made of newly formed jets and tori in proto/young planetary nebulae using ultra high resolution (roughly 0.3 arc sec) millimeter interferometry. Spectro-imaging of the molecular gas will be carried out in lines of 12CO, 13CO, and other molecular species to determine the geometry, mass, and dynamics of the jets and tori, and their inter-relations. The observations will be used to provide general constraints and to test specific scenarios of the final mass loss and jet formation. The results are expected to substantially improve our understanding of this key phase of stellar evolution. This project will impact other fields of astrophysics as planetary nebulae constitute a new class of objects with jets, whose distinct characteristics may offer novel insights on how jets can form. This project also involves the education and research training of graduate and undergraduate students at New York University. It further fosters international scientific co-operation, and forms the basis for Professor Huggins' on-going outreach efforts which are broadly centered on stellar evolution. This includes "Stars in the Curriculum," a collaborative program with an education specialist and practicing teachers, designed to enhance the science curriculum in public schools in New York City.