A Coordinated Laboratory and Astronomical Study of the Seeds of Dust Formation in Giant and Supergiant Stars

天文学家通过将观测到的无线电信号与在地球上进行的测量相匹配来识别太空中的分子。通过这种方法，在我们的银河系中已经发现了近200个简单分子(如水和氨)。在这项研究中，科学家们将对射电望远镜可以探测到的新分子进行仔细的实验室测量。他们将对分子的信号进行非常精确的测量，然后用望远镜在太空中搜索这些信号。科学家们将通过观察恒星周围的气体云来寻找这些分子，这些气体云将碳、氧和其他元素从恒星外层吹走。当来自恒星的气体冷却时，分子就会形成，其中一些分子随后会积累起来，形成一团被称为“尘埃”的物质。这些科学家将了解这些恒星周围的太空中形成了哪些类型的分子。他们对地球上熟悉但在太空中未知的分子特别感兴趣，如硅氧化物(例如沙子)、氧化铝(未涂漆的铝上的白色薄膜)和二氧化钛(油漆中的白色和防晒霜的活性成分)。其中一些硅、铝和钛的氧化物被认为是尘埃的基石，这些尘埃最终形成了我们太阳系外的行星。这项研究首先在实验室测量了含有两个或三个硅、铝或钛原子的新复杂分子的转动光谱。这些分子比以前测量的要复杂得多。下一步，射电天文学家将解开晚型富碳富氧演化恒星内部包层中的化学物质，这些恒星是行星形成尘埃的主要来源。由于这些源的化学模型中有许多不确定性，天文学家只有通过经验方法才能理解这些复杂的区域，这种方法需要高角度分辨率和高灵敏度的实验室测量和天文观测的综合计划。这些分子将在广泛使用的实验室源(辉光放电、放电喷嘴或激光烧蚀)中产生；它们的旋转光谱将用法布里-珀罗腔、宽带啁啾脉冲光谱仪或非共振吸收池在厘米、毫米和亚毫米波段测量；光谱将用标准哈密顿和计算机程序进行分析。实验室中寻找新分子物种的工作将由我们的专家合作者对结构进行高水平的量子化学计算来指导，并将利用我们团队在天体物理感兴趣的反应性分子方面30年的工作。除了这项工作对天文学的贡献外，在实验室中直接检测难以捉摸的钛氧化物、铝氧化物和含硅分子将提供有关它们结构的详细信息，这反过来将帮助应用物理学家解决有关支配生长的基本反应及其广泛的光催化和光伏应用的棘手问题。这项研究结合了化学、电子学、物理学和天文学，是教学、培训和学习的极好课题。外展计划有两个方面：(1)通过史密森天体物理天文台(SAO)和哈佛大学的项目，为本科生和研究生提供导师和研究机会；(2)为创新的学习工具创建一个谱线分子射电天文学模块，称为“频谱探索者”。光谱资源管理器是一个基于浏览器的光谱可视化和分析工具。Spectral Explorer将在高中课堂和公共外展学习环境中使用。圣保罗科学教育局(SED)正在开发这些活动。作为这项工作的一部分，SAO光谱学实验室将积极参与具体教程、视频、光谱数据集和案例研究资源的规划和执行，这些资源将集中在本提案所述的研究上。光谱探索者实验室将通过与NSF、NASA和Smithsonian附属网络的伙伴关系向目前使用SED资源的1万名教育工作者和50,000多名公众/公民科学用户传播。

Astronomers identify molecules in space by matching observed radio signals with measurements made on Earth. By this method, nearly 200 simple molecules (such as water and ammonia) have been identified in our Milky Way galaxy. In this research, scientists will make careful laboratory measurements of new molecules that could be detected by radio telescopes. They will make very precise measurements of the molecules' signature, then go to telescopes to search for these signals in space. The scientists will search for these molecules by observing clouds of gas surrounding stars which blow carbon, oxygen and other elements off their outer layers. Molecules form as the gas from stars cool, and some of these molecules subsequently accumulate and form clumps called 'dust'. These scientists will learn what types of molecules are formed in space around these stars. They are particularly interested in molecules familiar on Earth but which are unknown in space, like silicon oxides (e.g. sand), aluminum oxide (the white film on unpainted aluminum) and titanium oxide (the white color in paint and active component in sunscreen). Some of these oxides of silicon, aluminum, and titanium are thought to be the building blocks of the dust that ultimately forms planets outside our own Solar System.This research begins with laboratory measurements of rotational spectra of new complex molecules containing either two or three silicon, aluminum, or titanium atoms. These molecules are more complex than those previously measured. Next radio astronomers will unravel the chemistry in the inner envelopes of late-type carbon- and oxygen-rich evolved stars, which are a major source of planet forming dust. Owing to many uncertainties in the chemical models of these sources, it is only through an empirical approach, which entails an integrated program of laboratory measurements and astronomical observations at high angular resolution and sensitivity, that astronomers may understand these complex regions. The molecules will be produced in widely used laboratory sources (either glow discharge, discharge nozzle, or laser ablation); their rotational spectra will be measured in the centimeter, millimeter, and sub-millimeter bands either with a Fabry-Perot cavity, broadband chirped pulse spectrometer, or non-resonant absorption cell; and the spectra will be analyzed with standard Hamiltonians and computer programs.The search for the new molecular species in the laboratory will be guided by high level quantum chemical calculations of the structures which will be done by our expert collaborators, and will draw on 30 years of work on reactive molecules of astrophysical interest by our group. In addition to the contribution of this work to astronomy, direct detection of elusive titanium oxides, aluminum oxides, and silicon-bearing molecules in the laboratory will provide detailed information about their structures, which in turn will help applied physicists address vexing questions about the elementary reactions that govern the growth and their wide range of photo-catalytic and photovoltaic applications.This research combines chemistry, electronics, physics and astronomy and is as an excellent topic for teaching, training, and learning. The outreach plan is two-pronged: (1) Provide mentorship and research opportunities to undergraduate and graduate students through programs at the Smithsonian Astrophysical Observatory (SAO) and Harvard; and (2) Create a spectral line molecular radio astronomy module for an innovative learning tool, called 'Spectral Explorer'. The Spectral Explorer is a browser-based spectra visualization and analysis tool. The Spectral Explorer will be used in both high school classroom and public outreach learning settings. The SAO Science Education Department (SED) is developing these events. As part of this effort, the SAO spectroscopy laboratory will be actively engaged in the planning and execution of specific tutorials, videos, spectral datasets, and case study resources which will be centered on the research described in this proposal. The Spectral Explorer lab will be disseminated via partnerships with the NSF, NASA and Smithsonian Affiliations networks to the ten thousand educators currently using SED resources and to the more than 50,000 public/citizen science users.