Probing mass loss mechanisms in AGB and post-AGB stars

AST 0307687 Bieging，John H. PI将继续研究中等质量恒星在演化后期的质量损失过程，重点是所谓的渐近巨星分支恒星，以及随后的膨胀导致行星状星云形成的阶段。PI将奋进了解这些演化恒星的物理过程，通过这些过程，脉动，冲击，非平衡化学和尘埃形成驱动恒星质量损失，并确定喷出的气体和尘埃的组成。 PI将使用带有灵敏的宽带分光偏振计的光学望远镜来测量光学偏振作为选定的演化恒星的波长的函数。这些恒星附近的尘埃颗粒反射的偏振光是非常接近星星的新形成尘埃的诊断。 模型和数据的比较应该给独特的强大的约束的位置和这些恒星的拱星环境中形成的尘埃的属性。此外，PI将获得关键分子发射线的毫米和亚毫米观测，以限制演化恒星的星周包络中分子的空间分布。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的脉冲驱动冲击决定了喷出物质的化学成分。 根据选定的分子发射线（气体温度和密度的示踪剂），附近明亮巨星的小样本的额外~1角秒分辨率图像将提供PI先前在其拱星包层中检测到的小尺度结构中的物理条件的信息。研究结果不仅在科学文献中传播，而且还通过公开讲座和展览向更广泛的社区传播，这些讲座和展览由斯图尔特天文台定期向我们的社区提供，重点是使感兴趣的公众能够接触到科学，并促进进一步的学习。这项研究有一个重要的教育功能，通过吸引本科生和研究生，并允许和鼓励他们参加科学会议，介绍他们参与的工作的结果。

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.