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现象，当辐射和传导的能量传输不足时，就会发生对流。它可以在地球大气层(例如积云)和地幔(大陆漂移)以及恒星内部找到，在那里它可以影响其外层包层的化学浓缩以及它们的主序列寿命。尽管取得了巨大的进展，但恒星内部的对流在一些重要方面仍然知之甚少，而且我们目前最好的物理理论(混合长度理论；MLT)在许多情况下都不够充分。研究小组将应用一种新的一维对流模型来改进对流的处理，特别是对流边界混合(CBM)引起的对流穿透或超射。这种方法有望改进对主序列寿命的估计，并更正确地理解大质量恒星核心内相邻的“燃烧”壳体如何通过对流交换物质和能量。该奖项还将支持开发适合本科生和准备上大学的高中生的教学软件和模块，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。该团队将努力通过消除标准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上一个奖项中开发的新的一维对流模型来实现。该模式采用了一个新的约束方程，可以改进对给定Schwarzschild边界处对流运动动能的对流穿透程度的估计。这个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。该团队将使用对流超射的这种更准确的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程序中实施的新约束方程来推进CBM，同时偶尔用简短但廉价的三维模拟来重新校准动能估计。通过使用这些定期重新校准，该程序从一维对流和CBM模型中消除了特别的自由参数，包括混合长度。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.