Radio Studies of Planetary Nebulae: Probing Radiation-driven Molecular Chemistry

恒星通过在核心将氢聚变成氦来产生能量。当一颗星星的氢供应耗尽时，这颗星星会急剧膨胀，成为一颗“红巨星”。红巨星产生的元素（如碳和氧）是我们所知的生命所必需的。红巨星的外层，由于引力的作用，与星星的核心只有微弱的联系，很容易被强烈的辐射从星星中驱逐出去。来自星星炽热核心的强烈紫外线辐射可以将喷出的红巨星气体变成一个巨大的发光等离子云，天文学家称之为“行星状星云”。一些行星状星云也含有丰富的化学物质混合物，以分子形式存在，可能类似于年轻地球的大气层。因此，每个行星状星云都给我们提供了恒星丰富宇宙生命基石的过程的快照。研究人员将利用射电望远镜对行星状星云的观测来确定释放到星际空间的分子气体混合物。这些结果将通过加深人类对生命的基本元素如何到达地球以及可能到达绕其他恒星运行的行星的理解来推进天文学领域。为了支持科学的教育和多样性，研究人员还将为初中和高中学生开发一个夏季短期课程，以解释天文学家如何确定星际气体的成分，并将产生行星状星云的展品，供世界各地的天文馆使用。分子内部的极端物理条件-丰富的行星状星云使这些几何形状简单的天体成为研究的沃土。 这些区域的图像有助于提高天文学家对（UV）光子主导区域（PDR）和X射线主导区域（XDR）中辐射驱动化学的理解。研究人员计划对辐射分子气体的关键示踪物进行全面的观测和建模，这些示踪物包括最近和研究最好的富含分子的行星状星云（PNe）。调查人员将充分利用单碟和干涉（亚）毫米波射电天文学设施，包括阿塔卡马大型毫米波阵列（阿尔马）的宽频率覆盖范围和宽视场测绘能力。研究人员将利用“现成的”建模代码来解释观测结果的分子气体分布，温度，密度和成分的目标PNe。这些结果将具有广泛的适用性，因为作为本研究重点的PNE中的PDR和XDR代表了各种各样的天体物理环境，从星星-在分子云内形成核心，形成围绕活动星系核的分子环面。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响进行评估，被认为值得支持审查标准。

Stars generate their energy through fusion of hydrogen to helium in their cores. When a star's hydrogen supply runs out, the star expands dramatically to become a "red giant". Red giants generate elements (like carbon and oxygen) that are essential for life as we know it. The outer layers of a red giant, which are only weakly bound to the star's core by gravity, are easily driven away from the star by its intense radiation. Intense ultraviolet radiation from the star's hot core then can turn the ejected red giant gas into a giant, glowing plasma cloud that astronomers call a "planetary nebula". Some planetary nebulae also contain a rich mixture of chemicals, in molecular form, that may resemble the atmosphere of the young Earth. Each planetary nebula thereby gives us a snapshot of the process by which stars enrich the Universe in the building blocks of life. The investigator will use radio telescope observations of planetary nebulae to determine the mixture of molecular gases that are released into interstellar space. The results will advance the field of astronomy by deepening human understanding of how the essential elements of life arrived on Earth and might arrive on planets orbiting other stars. To support education and diversity in the sciences, the investigator will also develop a summer short course for middle and high school students to explain, among other things, how astronomers determine the compositions of interstellar gases, and will generate exhibits about planetary nebulae for use in planetariums around the world.The extremes of physical conditions within molecule-rich planetary nebulae make these geometrically simple objects particularly fertile ground for research. Images of these regions aid in improving astronomers' understanding of radiation-driven chemistry in (UV) photon-dominated regions (PDRs) and X-ray-dominated regions (XDRs). The investigator plans a comprehensive campaign of observations and modeling of key tracers of irradiated molecular gas for a sample comprising the nearest and best-studied molecule-rich planetary nebulae (PNe). The investigator will fully exploit the broad frequency coverage and wide-field mapping capabilities of single-dish and interferometric (sub)mm-wave radio astronomy facilities, including the Atacama Large Millimeter Array (ALMA). The investigator will make use of "off-the-shelf" modeling codes to interpret the observational results in terms of molecular gas distributions, temperatures, densities, and compositions within the target PNe. The results will have broad applicability, given that the PDRs and XDRs in the PNe, that are the focus of this study, are representative of a diverse array of astrophysical environments, from star-forming cores within molecular clouds to molecular tori surrounding active galactic nuclei.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.