Collaborative Research: The Coeval Degenerates Survey

合作研究：当代堕落调查

• 批准号: 1908723
• 负责人: Jennifer van Saders
• 金额: $ 25.34万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1908723&HistoricalAwards=false
• 关键词: Collaborative; Research; Coeval; Degenerates; Survey

The lowest mass stars in the Milky Way galaxy, K and M type stars ("cool dwarfs") are the most abundant, long-lived stars in the galaxy. It is important for astronomers to be able to precisely measure their ages in order to help answer the questions: "What is the fossil record of the assembly of our galaxy from the first stars to the present?" and "How diverse are planetary systems?" Cool dwarfs are sufficiently long-lived that they carry a record of star formation and chemical evolution over the entire history of the galaxy. Furthermore, Earth-sized transiting planets in the habitable zones of M dwarfs are easier to detect than planets orbiting Sun-like stars, but the ages of their host stars are much more difficult to measure. A research collaboration between the University of Hawai'i and Boston University will develop stellar rotation-based tools to infer precise ages for old (4 billion year-old) K and M type stars. They will do this by studying wide binary star systems containing both a white dwarf (WD) star and a star still on the main sequence (MS) of stellar evolution. Rotation can be measured in the main-sequence star, and an independent age of both stars can be inferred using the white dwarf. The investigators will also directly engage high-school students in scientific research through the HISTAR program at the University of Hawai'i. Students will have the opportunity to experience ownership over an individual stellar system, while working to contribute to the broader goal of building a timeline of galactic events and planetary system evolution. Students will work with data obtained on the summits of Hawaii's mountains, and interact with colleagues at Boston University.The spin-down of stars with time is a promising age-dating tool, but can only be used if the relationship between age and rotation can be properly calibrated. Currently, a primary limitation is the lack of empirical anchors of known age for these old, low-mass stars. This project will leverage wide WD+MS binaries to provide rotation and age calibrators. Total white dwarf ages are the combination of the time spent cooling as a dead core and the progenitor system's hydrogen and helium burning lifetimes. Both quantities are readily inferred from existing models and initial-final mass relations. These binaries provide the leverage to extend period-age relations out to the age of the galactic disk. Gaia DR2 has enabled the identification over one thousand bright (G 15 mag), nearby ( 200 pc) WD+MS systems widely separated enough to have never interacted. First, the researchers will use ground-based archival light curves to measure rotation periods of the main-sequence companions and spectroscopically characterize the white dwarfs to determine total system ages. In total, it will develop a sample of 50-100 calibration systems. Second, this proposal will explore systematic uncertainties in the ability of white dwarfs to deliver reliable old ages by studying coeval pairs of wide WD+WD binaries. Finally, it will confront existing models for stellar spin down with empirical anchors, and develop the first calibrated period-age relation for old (4 Gyr), low-mass (0.8 solar-mass) stars.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.

银河系中质量最低的恒星，K型和M型恒星（“冷矮星”）是银河系中数量最多、寿命最长的恒星。对于天文学家来说，能够精确地测量它们的年龄是很重要的，因为这有助于回答以下问题：“我们银河系从第一批恒星到现在的组合化石记录是什么？”以及“行星系统有多多样化？”冷矮星的寿命足够长，它们携带着整个星系历史上恒星形成和化学演化的记录。此外，与环绕类太阳恒星运行的行星相比，位于M矮星宜居带的地球大小的凌日行星更容易被探测到，但它们的主恒星的年龄却很难测量。夏威夷大学和波士顿大学之间的一项研究合作将开发基于恒星旋转的工具，以推断老年（40亿岁）K型和M型恒星的精确年龄。他们将通过研究包含一颗白矮星（WD）和一颗仍在恒星演化主序星（MS）上的恒星的宽双星系统来做到这一点。可以测量主序星的旋转，并且可以通过白矮星推断出两颗恒星的独立年龄。研究人员还将通过夏威夷大学的HISTAR项目直接让高中生参与科学研究。学生将有机会体验对单个恒星系统的所有权，同时努力为建立银河系事件和行星系统演化的时间轴这一更广泛的目标做出贡献。学生们将使用在夏威夷山峰上获得的数据，并与波士顿大学的同事互动。随着时间的推移，恒星的自转下降是一种很有前途的年龄测定工具，但只有在年龄和自转之间的关系能够得到适当校准的情况下才能使用。目前，一个主要的限制是缺乏这些古老的、低质量恒星已知年龄的经验锚点。该项目将利用宽WD+MS二进制文件来提供旋转和年龄校准器。白矮星的总年龄是作为一个死核冷却的时间和前身系统的氢和氦燃烧寿命的总和。这两个量都很容易从现有的模型和初始-最终质量关系中推断出来。这些双星提供了将周期-年龄关系延伸到星系盘年龄的杠杆。盖亚DR2已经能够识别超过1000个明亮的（g15等），附近（200pc）的WD+MS系统，它们彼此分隔得足够远，从未相互作用。首先，研究人员将使用地面档案光曲线来测量主序伴星的旋转周期，并对白矮星进行光谱表征，以确定系统的总年龄。总共将开发50-100个校准系统的样本。其次，该提案将通过研究同时期的宽WD+WD双星来探索白矮星提供可靠老年能力的系统不确定性。最后，它将用经验锚点来对抗现有的恒星自旋下降模型，并为年老（4 Gyr）、低质量（0.8太阳质量）恒星建立第一个校准的周期-年龄关系。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。

项目成果

Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars

核心包络解耦驱动冷恒星中的径向剪切发电机

• DOI: 10.3847/2041-8213/acd780
• 发表时间: 2023
• 期刊: The Astrophysical Journal Letters
• 作者: Cao, Lyra;Pinsonneault, Marc H.;van Saders, Jennifer L.
• 通讯作者: van Saders, Jennifer L.

Testing White Dwarf Age Estimates Using Wide Double White Dwarf Binaries from Gaia EDR3

• DOI: 10.3847/1538-4357/ac78d9
• 发表时间: 2022-05
• 期刊: The Astrophysical Journal
• 作者: T. Heintz;J. Hermes;K. El-Badry;Charlie Walsh;J. V. van Saders;C. Fields;D. Koester