Probing mass loss mechanisms in AGB and post-AGB stars

探索 AGB 和后 AGB 恒星的质量损失机制

• 批准号: 0307687
• 负责人: John Bieging
• 金额: $ 15.4万
• 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: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0307687&HistoricalAwards=false
• 关键词: Probing; mass; loss; mechanisms; AGB

AST 0307687Bieging, John H.The PI will continue a research program on mass loss processes in intermediate mass stars in the late stages of their evolution, with emphasis on the so-called asymptotic giant branch stars, and the subsequent stages where expansion leads to formation of planetary nebulae. The PI will endeavor to understand the physical processes in these evolved stars by which pulsation, shocks, non-equilibrium chemistry, and dust formation drive the stellar mass loss and determine the composition of the ejected gas and dust. The PI will use optical telescopes with a sensitive, wide-band spectropolarimeter to measure the optical polarization as a function of wavelength for a selection of evolved stars. Polarized light reflected off dust grains near such stars is a diagnostic of newly-formed dust very close to the star. Comparison of models and data should give uniquely powerful constraints on the location and properties of dust formed in the circumstellar environment of these stars. Furthermore the PI will obtain mm and submm observations of key molecular emission lines to constrain the spatial distribution of molecules in the circumstellar envelopes of the evolved stars. One key goal of this study will be to test whether the molecular abundances and excitation conditions imply that pulsation-driven shocks in the stellar atmosphere determine the chemical composition of the ejected matter. Additional ~1 arcsec resolution images of a small sample of bright nearby giant stars in light of selected molecular emission lines that are tracers for gas temperature and density will give information on the physical conditions in the small-scale structures detected previously by the PI in their circumstellar envelopes Broader impact: The results are disseminated not only in the scientific literature, but also to the wider community via public lectures and displays, routinely provided by the Steward Observatory to our community, with an emphasis on making the science accessible to the interested public, and on stimulating further learning. This research has an important education function by engaging both undergraduate and graduate students, and by allowing and encouraging them to attend scientific meetings to present the results of the work in which they participated.

AST 0307687Bieging，John H.PI 将继续一项关于中等质量恒星在演化后期的质量损失过程的研究计划，重点是所谓的渐近巨分支恒星，以及膨胀导致行星状星云形成的后续阶段。 PI将努力了解这些演化恒星中的物理过程，脉动、冲击、非平衡化学和尘埃形成驱动恒星质量损失，并确定喷射气体和尘埃的成分。 PI 将使用带有灵敏宽带分光偏振计的光学望远镜来测量选定演化恒星的光学偏振与波长的函数关系。这些恒星附近的尘埃颗粒反射的偏振光可以诊断出非常靠近恒星的新形成的尘埃。 模型和数据的比较应该对这些恒星的星周环境中形成的尘埃的位置和性质给出独特的强有力的约束。此外，PI还将获得关键分子发射线的毫米和亚毫米观测结果，以限制演化恒星星周包层中分子的空间分布。这项研究的一个关键目标是测试分子丰度和激发条件是否意味着恒星大气中脉动驱动的冲击决定了喷射物质的化学成分。 根据选定的分子发射线（气体温度和密度的示踪剂），对附近明亮巨星的小样本进行约 1 角秒分辨率的额外图像，将提供有关 PI 先前在其星周包层中检测到的小规模结构的物理条件的信息。 更广泛的影响：结果不仅在科学文献中传播，而且还通过斯图尔德天文台定期提供的公开讲座和展示向更广泛的社区传播 向我们的社区开放，重点是让感兴趣的公众能够接触到科学，并鼓励进一步学习。这项研究具有重要的教育功能，它吸引了本科生和研究生，并允许和鼓励他们参加科学会议来展示他们所参与的工作成果。