Planetary Nebulae as Agents of Neutron-Capture Element Enrichment of the Galaxy

行星状星云作为银河系中子捕获元素富集的媒介

• 批准号: 0406809
• 负责人: Harriet Dinerstein
• 金额: $ 25万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0406809&HistoricalAwards=false
• 关键词: Planetary; Nebulae; Agents; Neutron; Capture

Planetary nebulae have been recently shown to display a range of chemical enrichments in light neutron-capture elements synthesized within their precursor stars during the so-called Asymptotic Giant Branch evolutionary phase. New spectroscopic tracers of the four elements in the atomic number range from Zinc to Krypton have been identified through infrared, optical, and ultraviolet spectroscopy, and their abundances derived. Some planetary nebulae show enhancements of up to factors of 10 to 20, while others show normal (solar system) values. By determining the enhancements of neutron-capture elements in planetary nebulae, we measure directly the composition of enriched material that is flowing into the interstellar medium from intermediate-mass stars, an important agent in driving the process of galactic chemical evolution. We also learn about the efficiency of dredge-up of nucleosynthetic products in evolved stars. This investigator is undertaking a multi-wavelength spectroscopic study that will more fully explore and establish the demographics of neutron-capture enrichments in planetary nebulae. The project involves both extending observations of the already identified optical and infrared lines to larger and more representative samples of these objects and searching for new lines from additional ions and elements. This study is testing current models for the late stages of stellar evolution that include crucial new physics such as convective overshoot and rotation (which also affect the stars' evolution in other ways, e.g. evolutionary tracks) and clarifying the nucleosynthetic sites for the first few neutron-capture elements, that lie between the iron-peak region and the heavier neutron-capture elements that are well-studied in stars.Broader Impact: The project addresses a key question identified in a 2002 report by the National Academy of Sciences Committee on the Physics of the Universe: How were the elements from iron to uranium made? The planetary nebula study establishes the end-point of enrichment after multiple dredge-up episodes, and, because it provides access to a nearly unexplored region of the periodic table, the project also provides unique data for the field of atomic spectroscopy, e.g. by determining precise energies for low-lying energy levels of poorly-studied ions, values for collisional cross-sections, and related atomic parameters. From the ratios of different elements, it may be possible to test nuclear reaction cross-sections, as well as to constrain the conditions under which the nucleosynthesis occurs. The project is also having an impact on the development of future scientists and a scientifically informed population. Two graduate students receive financial support, and undergraduate students, including ethnic minorities and women, are trained in specific techniques so that they can work on well-defined small projects. The excitement of this work is conveyed to middle and high school students, who are just becoming acquainted with the idea of chemical elements, through coordination with local schools with magnet science programs, and involve either a graduate or undergraduate student in this effort.

最近，行星状星云显示出在所谓的渐近巨星分支演化阶段期间在其前身恒星内合成的轻中子捕获元素的一系列化学富集。通过红外、光学和紫外光谱鉴定了原子序数范围从锌到氪的四种元素的新光谱示踪剂，并得出了它们的丰度。 一些行星状星云显示出高达 10 到 20 倍的增强，而另一些则显示出正常（太阳系）值。通过确定行星状星云中中子捕获元素的增强，我们直接测量从中等质量恒星流入星际介质的浓缩物质的成分，这是驱动银河化学演化过程的重要因素。我们还了解了演化恒星中核合成产物的挖掘效率。 该研究人员正在进行一项多波长光谱研究，该研究将更全面地探索和建立行星状星云中中子捕获富集的人口统计数据。该项目涉及将对已识别的光学和红外线的观察扩展到这些物体的更大且更具代表性的样本，并从其他离子和元素中寻找新的谱线。这项研究正在测试恒星演化后期的当前模型，其中包括重要的新物理，例如对流超调和旋转（这也以其他方式影响恒星的演化，例如演化轨迹），并澄清最初几种中子捕获元素的核合成位点，这些元素位于铁峰区域和恒星中已得到充分研究的较重中子捕获元素之间。更广泛的影响： 该项目解决了美国国家科学院宇宙物理委员会 2002 年报告中提出的一个关键问题：从铁到铀的元素是如何形成的？ 行星状星云研究确定了多次挖掘事件后的浓缩终点，并且由于它提供了进入元素周期表中几乎未探索的区域的途径，因此该项目还为原子光谱领域提供了独特的数据，例如通过确定研究不足的离子的低能级的精确能量、碰撞截面的值以及相关的原子参数。根据不同元素的比例，可以测试核反应截面，并限制核合成发生的条件。该项目还对未来科学家和具有科学知识的人群的发展产生影响。 两名研究生获得经济支持，本科生（包括少数民族和女性）接受特定技术的培训，以便他们能够从事明确的小型项目。通过与当地学校的磁体科学项目协调，并让研究生或本科生参与这项工作，这项工作的兴奋感被传达给刚刚熟悉化学元素概念的中学生和高中生。