Collaborative Research: Understanding Stellar Structure Using Lithium and New Steps Toward the Big Bang Lithium Abundance

相对于氢，锂的丰度是早期宇宙大爆炸模型的一个关键预测。元素的丰度可以用恒星光谱中的吸收线来测量。但是，当对流将恒星表面物质与较热的恒星内部物质混合时，锂也会在恒星中被破坏。在那些预计不会发生锂耗尽过程的恒星中，可以看到恒星大气中锂的丰度很低，而在那些预计会发生锂耗尽过程的恒星中，锂的丰度远低于预期。为了更好地了解恒星内部的物理过程，该团队将测量精心挑选的恒星样本大气中锂的丰度。他们希望确定太阳的质量和年龄是正常的还是不正常的恒星，在被认为相同的恒星中，锂的破坏是否存在差异，并更好地理解从微波背景观测中推断出的大爆炸锂丰度与在恒星大气中看到的锂丰度之间的差异。这是四所大学天文学家的合作成果，其中包括一所以本科生为主的大学。该项目将产生至少一篇博士论文，并通过将一个学生团队整合到一个大规模的研究项目中，利用亚利桑那州、加利福尼亚州和澳大利亚的天文台，扩大各个学院本科生的教育机会。研究小组将扩展其对疏散星团和球状星团中恒星的光谱研究，重点是老疏散星团M67和NGC188，以及最近的球状星团NGC6397。他们的目标是(a)确定太阳的质量和年龄是正常还是异常的恒星，(b)确定在被认为相同的恒星之间控制锂破坏的物理机制是否存在差异，(c)对恒星金属含量在确定锂耗尽水平中的作用进行开创性研究，以及(d)研究恒星演化对晕中金属缺乏恒星的潜在影响。这意味着从微波背景推断出的大爆炸锂丰度值与从晕矮星表面推断出的锂丰度值之间的真实分歧程度（如果有的话）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The abundance of Lithium, relative to Hydrogen, is a key prediction of Big Bang models of the early universe. Abundances of the elements can be measured using the absorption lines in stellar spectra. But Lithium can also be destroyed in stars when convection mixes surface material with the hotter stellar interiors. Low abundance of Lithium in stellar atmospheres is seen among stars where processes that deplete Lithium would not be expected to occur, and abundances are far lower than predicted for stars where such depletion processes are expected to be operating. This team will measure the abundance of Lithium in the atmospheres of a carefully selected sample of stars in order to better understand physical processes inside stars. They hope to determine whether the Sun is a normal or abnormal star for its mass and age, whether there is variation in Lithium destruction among supposedly identical stars, and better understand the disagreement between the Big Bang Lithium abundance inferred from the microwave background observations and that seen in stellar atmospheres. This is a collaborative effort among astronomers at four universities, including a predominantly undergraduate institution. This project will lead to at least one PhD thesis and extend the educational opportunities for undergraduates at the individual schools by integrating a team of students in a large-scale research program, using astronomical observatories in Arizona, California, and Australia.The research team will extend and expand its spectroscopic studies of stars in open and globular clusters, emphasizing the old open clusters M67 and NGC188, and the nearest globular cluster, NGC6397. Their goals are (a) determine whether the Sun is a normal or abnormal star for its mass and age, (b) determine if there is variation in the physical mechanisms controlling Li destruction among supposedly identical stars, (c) pioneer studies on the role of stellar metal content in determining the level of Li-depletion, and (d) study the potential impact of stellar evolution on metal deficient stars of the halo, with implications for the true level of disagreement (if any) between the value of the Big Bang Li abundance inferred from the microwave background versus that inferred from halo dwarf surface Li abundances.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.