Investigating the Chemistry of Circumstellar Material through Millimeter-wave Observations and Laboratory Spectroscopy

Ziurys博士和她的团队的这项研究的目标是：i）通过毫米波观测继续探测星周包层的物理和化学性质，ii）通过实验室光谱学识别新的星周耐火分子，以及iii）对较老的PNe进行更详细的观测，以确定其分子组成的范围。在气体、尘埃和较重的元素中，通过核合成在这些物体中产生。星周壳的化学和物理特性对ISM中致密物质的整个生命周期以及银河系的化学演化有着重大影响。 星周包层中的化学成分与分子云中的化学成分完全不同，分子云的部分特征是可能与尘埃颗粒形成有关的难熔化合物。对星周分子的研究已经使人们对恒星质量损失过程有了深入的了解。大多数演化恒星的残余外壳成为行星状星云（PNe），其形态和化学演化以及对弥漫云形成的影响尚未得到很好的理解。大约有一半的星周包层是富氧的，包括超巨星和超巨星，以及早期的AGB恒星，但还没有像富碳恒星那样得到很好的研究。 富氧天体代表了恒星演化的不同阶段。Ziurys的团队先前在毫米波长下对超巨星星星VY Canis Majoris（VY CMa）的富氧包层进行了深入研究。 这里的工作建立在第一次详细研究的基础上，将调查超巨星NML天鹅座和E-AGB恒星TX Cam和R Leo的富O拱星壳。S型星星chi Cygnus的包层也将被研究，以探索碳和氧丰度大致相等时的化学变化。 将使用亚利桑那射电天文台亚毫米望远镜的高灵敏度ALMA型接收器，通过1毫米宽波段测量（215至285千兆赫）对这些天体进行研究，并将结果与VY CMa和富碳天体IRC+10216已经获得的结果进行比较。光谱分析使用辐射传输方法，使用开发的代码来解释多个，非球形风，分子丰度，分布和温度将被确定。VY CMa和IRC+10216的观测揭示了这些天体中数百条不明谱线，可能来自难熔分子。实验室工作将需要测量潜在的星周难熔化合物的纯旋转光谱，例如富氧壳的氧化物（ScO、TiOH、KO）、IRC+10216中可能存在的金属二碳化物MC 2（M = Al、Fe、Na、Mg）和S型天体的氮化物（MgN、AlN和NaN）。一旦建立，将通过与亚利桑那州月球和行星实验室的合作，将星周气相耐火分子的清单与陨石中发现的星周颗粒的固态成分进行比较。将在ARO SMT和12 m处对分子HCO+、CS、C3 H2和H2 CO中的旧PNe（Ring、Dumbell、M2-46）样品进行观察，以更全面地表征PNe的分子含量。拟议的单碟工作是准备和补充阿尔马调查。Ziurys集团有一个积极的计划，在实验室光谱集中在这种不寻常的，反应性的物种，与四个工作光谱仪：三个直接吸收和一个傅立叶变换微波系统与激光烧蚀源的金属。 这项工作将观测研究与实验室天体物理学直接联系起来，并且是非常跨学科的。研究生培训涉及天文学和实验室实验两个方面，将有几名女学生参加。Ziurys博士正在开发天体化学的跨学科课程和一个说明基本分子光谱学的网站。

The goals of this study by Dr. Ziurys and her group are to i) continue to probe the physical and chemical properties of circumstellar envelopes through mm-wave observations, ii) identify new circumstellar refractory molecules through laboratory spectroscopy, and iii) conduct more detailed observations of older PNe to determine the extent of their molecular composition.Mass loss from circumstellar envelopes of evolved stars enriches the interstellar medium (ISM) in gas, dust, and the heavier elements that are created in these objects through nucleosynthesis. The chemical and physical characteristics of circumstellar shells have major impacts on the overall life cycle of dense material in the ISM, as well as Galactic chemical evolution. The chemistry in circumstellar envelopes is quite different from that in molecular clouds, characterized in part by refractory compounds that are likely related to dust grain formation. Studies of circumstellar molecules have already given insight into the stellar mass loss process. The remnant shells of most evolved stars become planetary nebulae (PNe), whose morphological and chemical evolution, and impact on diffuse cloud formation are not yet well understood. About half of circumstellar envelopes are oxygen-rich, including those of supergiants and hypergiants, and early AGB stars, but are not yet that well studied as their carbon-rich counterparts. The oxygen rich objects represent different stages in stellar evolution.The Ziurys' group previously conducted an in-depth investigation of the O-rich envelope of the supergiant star, VY Canis Majoris (VY CMa)at millimeter wavelengths. The work here builds on this first detailed study and will be investigate the O-rich circumstellar shells of the supergiant NML Cygnus and the E-AGB stars TX Cam and R Leo. The envelope of the S-type star chi Cygnus will also be studied to explore chemical changes when carbon and oxygen abundances are about equal. These objects will be investigated via 1 mm broad-band surveys (215 to 285 GHz), using the highly sensitive ALMA-type receiver at the Sub-millimeter Telescope of the Arizona Radio Observatory (ARO), and the results compared with those already obtained for VY CMa and the carbon-rich object IRC+10216. The spectra are analyzed using radiative transfer methods, using a code developed to account for multiple, non-spherical winds, and molecular abundances, distributions, and temperatures will be determined. The surveys of VY CMa and IRC+10216 have revealed hundreds of unidentified lines in these objects, likely arising from refractory molecules. The laboratory work will entail measurements of the pure rotational spectra of potential circumstellar refractory compounds, such as oxides (ScO, TiOH, KO) for O-rich shells, metal dicarbides MC2 (with M = Al, Fe, Na, Mg)which are likely species in IRC+10216, and nitrides (MgN, AlN, and NaN) for the S-type objects. Once established, the inventory of circumstellar gas-phase refractory molecules will be compared with the solid state composition of circumstellar grains found in meteorites, through a collaboration with Arizona's Lunar and Planetary Lab. Observations of a sample of older PNe (Ring, Dumbell, M2-46) in the molecules HCO+, CS, C3H2, and H2CO will be carried out at the ARO SMT and 12 m in order to more fully characterize the molecular content of PNe. The proposed single-dish work is both preparatory for and complementary to ALMA investigations.The Ziurys group has an active program in laboratory spectroscopy centered on such unusual, reactive species, with four working spectrometers: three direct absorption and one Fourier transform microwave system with a laser ablation source for metals. This work directly links observational studies with laboratory astrophysics, and is very interdisciplinary. Graduate student training involves both astronomical and laboratory experimental aspects, and several female students will be participating. Dr. Ziurys is developing interdisciplinary courses in Astrochemistry and a website illustrating basic molecular spectroscopy.