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

通过毫米波观测和实验室光谱研究星周材料的化学

基本信息

批准号：
1211502
负责人：
Lucy Ziurys
金额：
$ 38.27万
依托单位：
University of Arizona
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2012
资助国家：
美国
起止时间：
2012-06-15 至 2016-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1211502&HistoricalAwards=false
关键词：
Investigating Chemistry Circumstellar Material through

项目摘要

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.

Ziurys 博士和她的团队进行这项研究的目标是：i) 继续通过毫米波观测探索星周包膜的物理和化学性质，ii) 通过实验室光谱学识别新的星周难熔分子，以及 iii) 对较老的 PNe 进行更详细的观察，以确定其分子组成的程度。演化恒星的星周包膜的质量损失丰富了星际介质 (ISM) 存在于气体、灰尘和这些物体中通过核合成产生的较重元素中。星周壳的化学和物理特性对ISM中致密物质的整体生命周期以及银河系化学演化具有重大影响。星际包层中的化学成分与分子云中的化学成分有很大不同，其部分特征是难熔化合物，这些化合物可能与尘埃颗粒的形成有关。对星周分子的研究已经深入了解了恒星质量损失过程。大多数演化恒星的残余壳层变成行星状星云（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富含氧，包括超巨星和超巨星以及早期 AGB 恒星的包层，但尚未像富含碳的对应物那样得到充分研究。这些富氧天体代表了恒星演化的不同阶段。Ziurys的研究小组此前在毫米波长下对超巨星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个详细研究的基础上，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。 S型天鹅座星的包层也将被研究，以探索碳和氧丰度大致相等时的化学变化。这些天体将通过 1 毫米宽带勘测（215 至 285 GHz）进行调查，使用亚利桑那射电天文台 (ARO) 亚毫米望远镜的高灵敏度 ALMA 型接收器，并将结果与已经为 VY CMa 和富碳天体 IRC+10216 获得的结果进行比较。使用辐射传输方法对光谱进行分析，使用为解释多重非球形风而开发的代码，并确定分子丰度、分布和温度。 VY CMa 和 IRC+10216 的调查揭示了这些物体中数百条未识别的线条，可能是由难熔分子产生的。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，例如富氧壳的氧化物（ScO、TiOH、KO）、金属二碳化物MC2（其中M = Al、Fe、Na、Mg）（可能是IRC+10216中的物质）以及S型天体的氮化物（MgN、AlN和NaN）。一旦建立，星周气相耐火分子的清单将通过与亚利桑那州月球和行星实验室的合作，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、C3H2 和 H2CO 中的较旧 PNe 样品（Ring、Dumbell、M2-46）进行观察，以便更全面地表征 PNe 的分子含量。拟议的单皿工作既是 ALMA 研究的准备，也是对 ALMA 研究的补充。Ziurys 小组在实验室光谱学方面有一个活跃的计划，以这种不寻常的活性物质为中心，有四个工作光谱仪：三个直接吸收和一个带有金属激光烧蚀源的傅里叶变换微波系统。这项工作将观测研究与实验室天体物理学直接联系起来，并且具有很强的跨学科性。研究生培养涉及天文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跨学科课程和一个介绍基本分子光谱学的网站。