Constraining the Evolutionary Pathways for White Dwarfs: Crystallization, Cooling Anomalies, and Mergers

白色矮星（WD）是像太阳这样的恒星的最终演化状态：星星的核燃料耗尽，核心在自身重力作用下收缩。WD最初形成时非常热，但由于没有能量来源，它会在数十亿年内逐渐冷却并结晶。WD为理解各种现象提供了必要的工具，包括Ia型超新星及其作为宇宙学距离指标的用途，单星和双星星星演化，以及银河系的星星形成历史。来自俄克拉荷马州大学的一个研究小组将专注于与WD冷却和进化的物理学有关的重要问题。该项目将通过两个教育目标产生更广泛的影响：1-首席研究员（PI）将继续他在俄克拉荷马州物理系月球早日外展组的大学工作，提供互动演示，讲座，问答小组，和观星活动，侦察组和K-12学生，包括夏延和阿拉帕霍部落的学生和2-这个项目将为研究生和本科生提供研究机会，使用盖亚卫星和斯隆数字巡天（SDSS）的数据，研究人员将对SDSS覆盖区内的WD进行新的光谱调查，并在100 pc内下降到5000 K的温度。同一个团队之前的一项调查获得了温度超过6000 K的白色矮星的光谱学：向较冷温度的扩展对于解决WD冷却物理学目前的挑战至关重要。新的调查将使研究小组能够获得这个较冷样品的WD质量和光度，包括所谓的“超冷”WD。将新冷却样品的光度和质量与WD冷却的演化模型进行比较，将使研究小组能够首次探测所有WD质量的重要物理学，如结晶，相分离和对流耦合。此外，他们将使用广泛的WD二进制文件和“大规模”WD来测试进化模型和WD合并率。这些是我们理解WD演变的一些最基本的问题。该奖项反映了NSF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。

White dwarfs (WD) are the final evolutionary state of stars like the sun: the star’s nuclear fuel is depleted and the core shrinks under its own gravity. A WD is very hot when it first forms but will gradually cool and crystallize over billions of years because it has no source of energy. WDs provide essential tools for understanding a variety of phenomena including type Ia supernovae and their use as cosmological distance indicators, single and binary star evolution, and the star formation history of the Galaxy. A team from the University of Oklahoma will focus on important questions pertaining to the physics of WD cooling and evolution. This project will achieve significant broader impact through two educational goals: 1- The Principal Investigator (PI) will continue his work at the University of Oklahoma Physics Department Lunar Sooner Outreach group, providing interactive demonstrations, lectures, question and answer panels, and stargazing events to scout groups and K-12 students, including the Cheyenne and Arapaho tribal students and 2- this project will provide research opportunities for graduate and undergraduate students, including members of under-represented groups.Using data from the Gaia satellite and the Sloan Digital Sky Survey (SDSS) the investigators will carry out a new spectroscopic survey of WDs in the SDSS footprint and within 100pc down to a temperature of 5000K. A previous survey by the same team obtained spectroscopy of white dwarfs hotter than 6000K: the extension to cooler temperatures is essential for resolving the current challenges in the cooling physics of WDs. The new survey will enable the team to obtain WD masses and luminosities for this cooler sample, including the so-called “ultracool” WDs. Comparing the luminosities and masses of the new cool sample to evolutionary models of WD cooling will allow the team to probe important physics such as crystallization, phase separation, and convective coupling for all WD masses for the first time. In addition, they will use wide WD binaries and “massive” WDs to test evolutionary models and WD merger rates. These are some of the most fundamental questions for our understanding of WD evolution.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.