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博士及其小组的这项研究的目标是i）继续通过MM波观测来调查双歧性信封的物理和化学特性，ii）确定通过实验室光谱验证的新异，通过实验室光谱进行，以及III）进行了更详细的观察，以确定其较旧的媒体损失。（ISM）通过核合成在这些物体中产生的气体，灰尘和较重的元素中。壳外壳的化学和物理特征对ISM中致密材料的整体生命周期以及银河化学演化产生了重大影响。折叠信封中的化学与分子云中的化学反应完全不同，部分原因是可能与灰尘颗粒形成有关的难治性化合物。偶尔分子的研究已经深入了解了恒星质量损失过程。大多数进化恒星的残余壳变成了行星星云（PNE），其形态和化学演化以及对弥漫性云形成的影响尚未得到充分了解。大约一半的星际信封是氧气丰富的，包括超级巨人和超级巨星和早期AGB恒星，但尚未像碳富含碳的同类产品那样进行。富含氧的物体代表了恒星进化中的不同阶段。这里的工作基于这项首次详细研究，并将研究超级巨星NML Cygnus和E-AGB Stars TX CAM和R Leo的O-Rich Interlar壳。当碳和氧气丰度相等时，还将研究S型星Chi Cygnus的包膜以探索化学变化。这些物体将通过1 mm的宽带调查（215至285 GHz）进行研究，使用亚利桑那无线电天文台的亚毫米望远镜（ARO）的高敏感的Alma型接收器（ARO），并且与已经获得的VY CMA和碳富含碳含量IRC IRC+102216的结果相比。使用辐射转移方法分析光谱，使用开发的代码来说明多种非球风，以及分子丰度，分布和温度。 VY CMA和IRC+10216的调查显示了这些物体中数百条未识别的线，这可能是由难治性分子引起的。 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.建立后，通过与亚利桑那州的月球和行星实验室的合作，将与陨石中的室外晶粒的固态组成进行比较，将其库存库存。将在HCO+，CS，C3H2和H2CO分子中对较老的PNE（RING，DUMBELL，M2-46）样品进行观察，在ARO SMT和12 m处进行，以更充分地表征PNE的分子含量。拟议的单次工作既准备了ALMA研究，又是互补的。Ziurys组在实验室光谱中具有积极的计划，以这种不寻常的反应性物种为中心，具有四个工作光谱仪：三个直接吸收和一个傅立叶变换微波系统，具有一个激光消融源的金属。这项工作直接将观察性研究与实验室天体物理学联系起来，并且非常跨学科。研究生培训涉及天文学和实验室实验方面，几名女学生将参加。 Ziurys博士正在开发星体化学的跨学科课程和一个说明基本分子光谱法的网站。