CAREER: A Comprehensive Study of Proto--Planetary Nebulae Dust Shells and the Development of Experimental Astronomy Programs at the University of Illinois

9733697梅克纳伊利诺斯大学的玛格丽特·梅克纳博士正在研究垂死恒星周围的原行星状星云尘埃壳，并为研究生和本科生开发实验天文学项目。该研究项目聚焦于中等质量恒星（0.8到8个太阳质量）恒星演化的后期阶段，解决了恒星天体物理学中两个长期存在的问题：什么物理机制驱动渐近巨型分支恒星质量损失？渐近巨大支星在质量损失过程中产生的星周尘埃的性质是什么？渐近巨星分支恒星质量损失的历史烙印在原行星状星云（恒星渐近巨星分支与行星状星云阶段过渡的天体）的星周尘埃壳中。为了弄清这段历史的最后一部分，梅克纳博士正在收集大约100个原行星状星云尘壳的红外数据。这些原行星状星云的地面中红外（波长0.8-2.5微米）图像显示了内部区域温暖尘埃（约300度K）的空间分布。利用激光制导自适应光学系统上的近红外成像仪（NIRIM）对这些原行星状星云中散射星光的空间分布进行了成像。一个模拟中心恒星和尘壳系统辐射传输的计算机程序，将被用来定量地推导出这些尘壳的三维几何形状及其内部半径。来自红外数据和哈勃太空望远镜图像的信息将用于制作计算机模型。几何形状的三维模型将提供对恒星最后死亡阵痛期间质量损失几何形状的深入了解。梅克纳博士等人对几个原行星状星云的初步研究表明，几何形状具有轴对称，这表明恒星在赤道平面上的质量损失速度比在极地区域要快。对尘埃壳内半径的观测数据被用来估计原行星状星云的动力学年龄。这些年龄将被用来测试其他科学家预测的恒星演化的理论时间尺度。这些理论上的时间尺度是不确定的，因为我们对主导这一阶段恒星演化的质量损失过程知之甚少。这些数据将用于约束星周尘埃特征的模型，包括尘埃的颗粒大小、组成和光学特性。在恒星渐近巨大分支质量损失过程中产生的星周尘埃是我们银河系中观测到的尘埃中最重要的贡献。我们银河系的下一代恒星就诞生于这种富含尘埃的星际介质中。因此，对尘埃组成的新认识将提高我们对星系演化的理解。与这个研究项目同时进行的，还有两个教育实验天文学项目正在开发中。红外天文学计划将通过让研究生和本科生参与原行星状星云的研究来扩大。这些学生将学习最新的红外观测技术。将开设一门新的天文学入门实验课程，名为《观察天空》。这将用于由非科学专业学生组成的大型入门课程。在本课程中，学生将通过在监督下的小组环境中进行观测来学习天文观测。

9733697 Meixner Dr. Margaret Meixner, of the University of Illinois, is investigating proto-planetary nebulae dust shells around dying stars and developing experimental astronomy programs for graduate and undergraduate students. The research program, which focuses on the late stages of stellar evolution of intermediate mass stars (0.8 to 8 Solar masses), addresses two long standing problems in stellar astrophysics: What physical mechanism drives the asymptotic giant branch star mass loss? What is the nature of the circumstellar dust created by the asymptotic giant branch star during mass loss? The history of asymptotic giant branch star mass loss is imprinted in the circumstellar dustshells of proto-planetary nebulae (objects in transition between the stellar asymptotic giant branch and planetary nebula phases). To discern the final part of this history, Dr. Meixner is collecting infrared data on approximately 100 proto-planetary nebulae dustshells. Ground-based, mid-infrared (0.8-2.5 micrometers wavelength), images of these proto-planetary nebulae show the spatial distribution of the warm (about 300 degree K) dust in the inner regions. The spatial distribution of the scattered starlight is imaged in these proto-planetary nebulae using the Near-InfraRed IMager (NIRIM) on a laser-guided adaptive optics system. A computer program, which models the radiative transfer in the central star and dustshell system, will be used to quantitatively derive the 3D geometries of these dustshells and their inner radii. The information from the infrared data and Hubble Space Telescope images will be used in making the computer models. The 3D models of the geometries will provide insight into the geometry of mass loss during the star's final death throes. A preliminary investigation of several proto-planetary nebulae by Dr. Meixner et al showed that the geometries had an axial symmetry and this indicated that the star's loss mass at a higher rate in the equatorial plane than in the polar region. The data from the observations of the dustshell inner radii are used to estimate the dynamical ages for the proto-planetary nebulae. These ages will be used to test the theoretical timescales of stellar evolution predicted by other scientists. These theoretical timescales are uncertain because the mass loss processes which dominate this stage of stellar evolution are poorly understood. These data will be used to constrain the models of the characteristics of circumstellar dust, including the grain sizes, the composition, and the optical properties of the dust. The circumstellar dust created during the asymptotic giant branch mass loss process in stars is the single most important contribution to the dust observed in our Galaxy. The next generation of stars in our Galaxy are born from this dust enriched interstellar medium. Hence, the new understanding about this dust composition will improve our understanding of galactic evolution. Concurrent with this research program, two educational experimental astronomy programs are being developed. The infrared astronomy program will be expanded by involving graduate and undergraduate students in research on proto-planetary nebulae. These students will learn the latest in infrared observing techniques. A new introductory astronomy laboratory course, entitled Observing the Sky, will be created. This will be used for the large introductory courses that are populated by non-science majors. In this course, the students will learn about astronomical observations by doing observations in a supervised, small-group environment.