Observational and Laboratory Studies of the Evolution of Circumstellar Material

在恒星演化的后期阶段，星周包层的质量损失是星际介质（ISM）富含气体、尘埃和重元素的主要途径。本课题将研究从渐近巨支恒星（AGB）到原行星状星云（PPNe）和行星状星云（PNe）的恒星喷射物的气相分子含量。研究人员将扩展他们正在进行的射电天文观测和实验室测量计划，以表征这些物体的分子库存和物理特性。该项目的结果将使天文学家了解恒星抛射物的性质及其对漫射ISM的影响。该项目将培养研究生和本科生掌握射电天文学和实验室天体物理学的先进技术。本研究项目旨在阐明分子材料如何从AGB阶段，通过中间的PPNe阶段，进化到高级的PNe阶段。为了实现这一目标，研究人员将进行：(1)通过对AGB星IRC+10216富碳包层的高灵敏度宽带毫米波调查进行广泛分析，更好地评估碳收支和同位素比率；(2)实验室测量无线电波段新含金属碳化物的旋转光谱，以帮助它们在星周包层中识别；(3)分析大犬维（VY Canis Majoris）在多种分子中富氧包膜的高空间分辨率图像，了解C/O比的影响；(4)利用射电天文观测对不同富碳富氧PPNe和PNe样品的分子组成和同位素组成进行评价。更好地了解恒星喷射物的性质，特别是星云星云，也将促进我们对它们如何丰富漫射ISM的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mass loss from circumstellar envelopes in the late stages of stellar evolution is a major avenue by which the interstellar medium (ISM) becomes enriched in gas, dust, and heavy elements. This research project will investigate the gas phase molecular content of stellar ejecta, from asymptotic giant branch (AGB) stars to protoplanetary nebule (PPNe) and planetary nebulae (PNe). The investigators will extend their ongoing program of radio astronomical observations and laboratory measurements to characterize the molecular inventory and physical properties of these objects. Results from the project will allow astronomers to understand the nature of stellar ejecta and their influence on the diffuse ISM. The project will train graduate and undergraduate students in advanced techniques of radio astronomy and laboratory astrophysics.This research program seeks to elucidate how molecular material evolves from the AGB phase, through the intermediate PPNe phase, to the advanced PNe phase. To accomplish this, the investigators will undertake: (1) a better assessment of the carbon budget and isotope ratios through an extensive analysis of a highly sensitive broadband millimeter-wave survey of the carbon-rich envelope of the AGB star IRC+10216; (2) laboratory measurements of the rotational spectra of new metal-bearing carbides in the radio band to aid their identification in circumstellar envelopes; (3) an analysis of high spatial resolution images of the oxygen-rich envelope of VY Canis Majoris in a variety of molecules to understand the influence of the C/O ratio; and (4) evaluation of the molecular and isotopic composition of a diverse sample of carbon-rich and oxygen-rich PPNe and PNe by radio astronomical observations. A better understanding of the nature of the stellar ejecta, particularly PNe, would also advance our understanding of how they enrich the diffuse ISM.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.