Exploring the Nucleosynthesis of Neutron-Capture Elements Through Nebular Spectroscopy

尼古拉斯·斯特林博士被授予美国国家科学基金会天文学和天体物理学博士后奖学金，在密歇根州立大学开展一项研究和教育计划。斯特林博士将对行星星云(PNE)和沃尔夫-瑞叶(WR)星云进行光谱研究，以研究S过程在这些天体的前体恒星中进行核合成时产生的中子(N)俘获元素(原子序数Z30)。他将在光学光谱区域观测到具有大范围前体质量的PNE，这提供了访问几个在恒星光谱中无法检测到的n俘获元素的途径。这些数据将被用来推导S过程浓缩因子，确定关键的物理条件，约束不同初始质量的PN前体恒星中S过程浓缩的逐元素模式，并揭示中等质量AGB星的S过程中子源。此外，斯特林博士还将观测红外线中的WR星云，以探测Se和Kr的发射线，这两种元素是弱S过程中浓缩程度最高的两种元素。这可能会提供第一批观测证据，证明大质量恒星中存在微弱的S过程。这些观测将得到实验室天体物理学研究的补充，以确定准确得出电离星云中n俘获元素BR和RB的丰度所需的原子数据。原子数据将被添加到最先进的光电离码的原子数据库中，并可供广大天体物理界使用。这项研究对宇宙中反铁元素的起源和化学演化，以及恒星演化后期的核合成和对流混合具有重要意义。此外，这项工作将建立一个观测和原子物理基础，在此基础上进行未来的星云研究，使这些元素在银河系和银河系外环境中的化学演化研究成为可能。斯特林还将在密歇根州立大学管理一个教育推广项目，包括为学生设计和教学研讨会，共同教授物理和天文学系课程，以及为本科生研究项目提供建议。研讨会的内容将在一系列级别上提供，将借鉴斯特林博士的研究活动，使大学生能够接触到它们。

Dr. Nicholas Sterling is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Michigan State University. Dr. Sterling will conduct a spectroscopic investigation of planetary nebulae (PNe) and Wolf-Rayet (WR) nebulae, in order to investigate the production of neutron(n)-capture elements (atomic number Z 30) by s-process nucleosynthesis in the progenitor stars of these objects. He will observe PNe with a wide range of progenitor masses in the optical spectral region, which provides access to several n-capture elements that are not detectable in stellar spectra. These data will be used to derive s-process enrichment factors, determine key physical conditions and constrain the element-by-element pattern of s-process enrichments in PN progenitor stars with different initial masses, and reveal the s-process neutron source in intermediate-mass AGB stars. In addition, Dr. Sterling will observe WR nebulae in the infrared in order to detect emission lines of Se and Kr, two of the most highly enriched elements by the weak s-process. This will potentially provide some of the first observational evidence of weak s-process enrichments in massive stars. These observations will be complemented by a laboratory astrophysics study to determine atomic data needed to accurately derive the abundances of the n-capture elements Br and Rb in ionized nebulae. The atomic data will be added to the atomic databases of state-of-the-art photoionization codes and made accessible to the broad astrophysical community. This research has implications for the origin and chemical evolution of trans-iron elements in the Universe, and nucleosynthesis and convective mixing during the late stages of stellar evolution. Moreover, this work will establish an observational and atomic physics foundation upon which future nebular studies can be built, enabling chemical evolution investigations of these elements in Galactic and extragalactic environs.Dr. Sterling will also manage an educational outreach program at Michigan State University comprised of designing and teaching seminars for students, co-teaching Physics and Astronomy Department courses, and advising an undergraduate student research project. The content of the seminars, which will be offered at a range of levels, will draw from the research activities of Dr. Sterling and make them accessible to university students.