Collaborative Research: CDS&E: 3-D Stellar Hydrodynamics of Convective Penetration and Convective Boundary Mixing in Massive Stars

对流是自然界中普遍存在的一种特征，当辐射和传导的能量传输不足时就会发生对流。它可以在地球的大气层（例如，积云）和地幔（大陆漂移）中找到，也可以在恒星内部找到，在那里它可以影响它们外层包裹层的化学富集以及它们的主序层寿命。尽管取得了巨大的进步，但恒星内部的对流在一些重要方面仍然知之甚少，我们目前最好的物理理论（混合长度理论；MLT）在许多情况下是不够的。研究小组将应用一种新的一维对流模型来改善对流的处理，特别是对流穿透或由于对流边界混合（CBM）而产生的超调。这种方法有望改善对主序生命周期的估计，并更正确地理解大质量恒星核心内邻近的“燃烧”壳如何通过对流交换物质和能量。该奖项还将支持适合本科生和即将进入大学的高中生的教学软件和模块的开发，以及参加参与机构的本科生的暑期研究。模拟数据也将提供给其他研究人员。该团队将通过消除标准MLT中出现的关键不确定性来提高对恒星演化的理解。这将通过应用他们在之前的奖项中开发的新的一维对流模型来完成。该模型采用了一种新的约束方程，在给定的史瓦西边界上对流运动的动能下，可以更好地估计对流穿透的程度。这种动能不能从一维恒星演化计算中得知，但可以通过一个简短的三维模拟准确而廉价地确定。该团队将利用这种更精确的对流超调表示来推进一维恒星演化模拟，从而通过使用动能估计和一维MESA代码中实现的新约束方程来推进CBM，同时偶尔使用短而廉价的三维模拟来重新校准动能估计。使用这些周期性重新校准，该程序消除了对流和CBM的一维模型中的特别自由参数，包括混合长度。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。

Convection is a ubiquitous feature in Nature and occurs whenever energy transport by radiation and conduction is insufficient. It can be found in the Earth's atmosphere (e.g., cumulus clouds) and mantle (continental drift), and inside stars, where it can impact the chemical enrichment of their outer envelopes as well their Main Sequence lifetime. Despite tremendous progress, convection within stars is still poorly understood in some important respects, and our current best physical theory (mixing length theory; MLT), is inadequate in many situations. The team of researchers will apply a new 1-D convection model to improve the treatment of convection, particularly convective penetration or overshooting due to convective boundary mixing (CBM). This approach promises improved estimates of Main Sequence lifetimes as well as a more correct understanding of how adjacent "burning" shells within the cores of massive stars exchange matter and energy through convection. The award will also support the development of instructional software and modules suitable for undergraduates and college-bound high school students as well as summer research by undergraduate students attending the participating institutions. Simulation data will also be made available to other researchers.The team will work to improve the understanding of stellar evolution by removing key uncertainties that arise in standard MLT. This will be done by applying a new 1-D model of convection developed in their previous award. This model employs a new constraint equation which enables an improved estimate of the extent of convective penetration for a given the kinetic energy of convective motions at the Schwarzschild boundary. This kinetic energy cannot be known from a 1-D stellar evolution computation but can be determined accurately and inexpensively through a short 3-D simulation. The team will advance 1-D stellar evolution simulations using this more accurate representation of convective overshooting, and hence of CBM, by using the kinetic energy estimates together with the new constraint equation implemented in 1-D MESA code, while occasionally recalibrating the kinetic energy estimates with short yet inexpensive 3-D simulations. Using these periodic recalibrations, this procedure eliminates ad hoc free parameters, including the mixing length, from the 1-D model of convection and CBM.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.