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：1)通过毫米波观测继续探测星周包膜的物理和化学性质；2)通过实验室光谱学识别新的星周难熔分子；3)对更老的PNe进行更详细的观察，以确定其分子组成的程度。演化恒星的星周包层的质量损失丰富了星际介质（ISM）中的气体、尘埃和通过核合成在这些天体中产生的较重元素。星周壳层的化学和物理特性对银河系致密物质的整体生命周期以及银河系的化学演化有着重要的影响。星周包层中的化学成分与分子云中的化学成分大不相同，分子云的部分特征在于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让我们了解了恒星质量损失的过程。大多数演化恒星的残壳形成行星状星云（PNe），其形态和化学演化以及对弥漫云形成的影响尚不清楚。大约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充分的研究。富氧天体代表了恒星演化的不同阶段。此前，Ziurys的研究小组对超巨星大犬星（VY CMa）的富含o的包层进行了毫米波长的深入研究。这里的工作建立在第一次详细研究的基础上，将研究超巨星NML天鹅座和E-AGB恒星TX Cam和R Leo的富含o的星周壳。研究人员还将研究s型恒星天鹅座的外壳，以探索碳和氧丰度大致相等时的化学变化。这些天体将使用亚利桑那射电天文台（ARO）亚毫米望远镜上的高灵敏度alma型接收器，通过1毫米宽带巡天（215至285 GHz）对其进行调查，并将结果与VY CMa和富碳天体IRC+10216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。对VY CMa和IRC+10216的观测揭示了这些天体中数百条未知的线，可能是由难解分子产生的。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o壳的氧化物（ScO, TiOH， KO），可能在IRC+10216中的金属二碳化物MC2 (M = Al, Fe, Na, Mg)，以及s型物体的氮化物（MgN， AlN和NaN）。一旦确定，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库存与陨石中发现的星周颗粒的固态组成进行比较。为了更全面地表征PNe的分子含量，将在ARO SMT和12 m上对一个较老的PNe样品（Ring、Dumbell、M2-46）在HCO+、CS、C3H2和H2CO分子中的表现进行观察。拟议的单碟工作既是ALMA调查的准备工作，也是对ALMA调查的补充。Ziurys团队有一个活跃的实验室光谱学项目，以这种不寻常的活性物质为中心，有四个工作光谱仪：三个直接吸收光谱仪和一个带有激光烧蚀源的傅立叶变换微波系统。这项工作直接将观测研究与实验室天体物理学联系起来，并且是非常跨学科的。研究生培训包括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介绍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.