Collaborative Research: Dust Formation Around Carbon Stars: Astromineralogy and the Condensation Sequence

这项研究的动机是需要更好地了解尘埃在天体物理环境中的作用。尘埃是恒星形成过程以及行星形成盘中的重要成分。它是演化恒星质量损失的一个来源（通过尘埃颗粒上的辐射压力），并将辐射场与星周物质密切相关。尘埃还有助于星际过程的几个方面，例如气体加热和分子形成。这里要进行的工作特别集中于表征冷碳恒星周围尘埃颗粒的精确性质，因为它们是银河系大部分富含碳尘埃的来源。通过了解这些恒星尘埃的初始状态，可以更准确地量化星际介质中尘埃的影响。此外，此类恒星周围相对良性的环境简化了化学反应，从而有助于理解运行中的各种过程。颗粒的特性也与恒星本身的演化有关，因此必须评估尘埃的精确性质才能理解这种演化。最后，最近斯皮策太空望远镜对麦哲伦星云中碳星的观测表明，与银河碳星相比，存在不同的尘埃凝结序列，这很可能允许研究金属丰度对尘埃形成的影响。这里要应用的工具包括红外光谱和成像、辐射传输模型、实验室光谱和档案数据挖掘。它们将用于测试当前碳星环境中尘埃形成的理论，以及母星的初始质量和金属丰度如何影响二次序列。此外，成像和辐射传输研究应深入了解行星状星云和原行星状星云中轴对称结构的原因。该项目包括一名博士生的参与和培训，该博士生将成为该研究项目的组成部分。学生将有望在会议和公开演讲中展示成果，从而将培训与公共宣传结合起来。

This research is motivated by the need to better understand the role of dust inastrophysical environments. Dust is a vital ingredient in the star formation process aswell as in planet forming disks. It is a source of mass loss from evolved stars (throughradiation pressure on dust grains) and intimately links the radiation field to thecircumstellar material. Dust also contributes to several aspects of interstellar processessuch as gas heating and the formation of molecules. The work to be undertaken here isspecifically centered on characterizing the precise nature of dust grains around coolcarbon stars as these are the source of the bulk of the Galaxy's carbon-rich dust. Byknowing the initial state of the dust from such stars, the effects of the dust in theinterstellar medium can be more accurately quantified. Moreover, the relatively benignenvironment surrounding such stars simplifies the chemistry, which in turn facilitates theunderstanding of the various processes in operation. The properties of the grains are alsotied to the evolution of the star itself, thus the precise nature of the dust must be assessedin order to understand this evolution. Finally, recent Spitzer Space Telescopeobservations of carbon stars in the Magellanic Clouds suggest a different dustcondensation sequence compared to Galactic carbon stars which may well permit theeffects of metallicity on dust formation to be investigated.The tools to be applied here include infrared spectroscopy and imaging, radiative transfermodeling, laboratory spectroscopy, and archival data mining. They will be used to testcurrent theories of dust formation in carbon star environments and how thesecondensation sequences are effected by the initial mass and metallicity of the parent stars.Furthermore, the imaging and radiative transfer studies should provide insight into thecauses of axisymmetric structures seen in planetary and protoplanetary nebulae.This project includes the participation and training of a doctoral student who will be anintegral part of the research program. The student will be expected to present results atboth conferences and public talks thereby combining training with public outreach.