Final Mass Loss on the AGB and Planetary Nebula Formation

该项目涉及普通恒星（1至8个太阳质量）从渐近巨星分支过渡到行星状星云阶段的演化过程中一个尚未解决的重要问题：最终质量损失的性质及其喷流的起源。增强的赤道质量损失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用于解决这一演化阶段的关键问题。1)AGB包层的几何形状：将在光学波长上进行深度成像，以确定渐近巨星分支尖端的星周包层的结构。结果将用于确定导致过渡的质量损失几何形状的长期演变，这提供了可能的射流触发机制的关键约束。2)喷气机和赤道托里：还将使用超高分辨率（约0.3弧秒）毫米干涉测量法对原始/年轻行星状星云中新形成的喷流和环面进行观测。分子气体的光谱成像将在12CO、13CO和其他分子种类的谱线上进行，以确定喷流和环面的几何形状、质量和动力学，以及它们之间的相互关系。观测结果将用于提供一般约束条件，并测试最终质量损失和射流形成的具体情况。这些结果有望大大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，因为行星状星云构成了一类新的具有喷流的物体，其独特的特征可能会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，并形成了哈金斯教授正在进行的以恒星演化为中心的外展工作的基础。这包括"课程之星"，这是一个与教育专家和实践教师合作的项目，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.