Observational and Laboratory Studies of the Evolution of Circumstellar Material

在恒星演化的后期，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。本研究项目将调查恒星喷出物的气相分子含量，从渐近巨星分支（AGB）恒星到原行星状星云（PPNe）和行星状星云（PNe）。 研究人员将扩大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清单和物理特性。 该项目的结果将使天文学家了解恒星喷出物的性质及其对弥漫ISM的影响。 该项目将培养研究生和本科生射电天文学和实验室天体物理学的先进技术。该研究计划旨在阐明分子材料如何从AGB阶段，通过中间PNe阶段，到高级PNe阶段的演变。 为了实现这一目标，研究人员将开展以下工作：（1）通过对AGB星星IRC+10216富碳包层的高灵敏度宽带毫米波测量进行广泛分析，更好地评估碳收支和同位素比率;（2）在无线电波段对新的含金属碳化物的旋转光谱进行实验室测量，以帮助在星周包层中识别它们;（3）分析大犬座VY的富氧包层的各种分子的高空间分辨率图像，以了解C/O比的影响;（4）通过射电天文观测评估富碳和富氧PNe和PNe的各种样品的分子和同位素组成。 更好地了解恒星喷出物的性质，特别是PNE，也将推进我们对它们如何丰富弥散ISM的理解。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.