Collaborative Research: The Coeval Degenerates Survey

银河系中质量最低的恒星，K型和M型恒星（“冷矮星”）是银河系中最丰富，寿命最长的恒星。对于天文学家来说，能够精确测量它们的年龄是很重要的，以帮助回答以下问题：“从第一颗恒星到现在，我们星系的化石记录是什么？”和“行星系统的多样性有多大？“冷矮星的寿命足够长，它们在整个银河系的历史中记录了星星的形成和化学演化。此外，在M矮星的适居带中，地球大小的凌日行星比绕类太阳恒星运行的行星更容易探测，但它们的宿主恒星的年龄却更难测量。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，以推断古老（40亿年）的K和M型恒星的精确年龄。他们将通过研究包含一颗白色（WD）星星和一颗仍在恒星演化主序（MS）上的星星的宽双星星星系统来做到这一点。主序星星星的自转可以被测量，而两颗恒星的独立年龄可以通过白色矮星来推断。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的更广泛目标做出贡献。学生们将使用在夏威夷山顶上获得的数据，并与波士顿大学的同事进行互动。恒星随时间的自旋下降是一种很有前途的年龄测定工具，但只有在年龄和旋转之间的关系可以正确校准的情况下才能使用。目前，一个主要的限制是缺乏已知年龄的经验锚，这些老，低质量的恒星。 该项目将利用广泛的WD+MS二进制提供旋转和年龄校准。 总的白色矮星的年龄是作为死核冷却的时间和祖先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。 这些双星提供了一个杠杆，将周期-年龄关系扩展到星系盘的年龄。盖亚DR 2已经能够识别超过一千个明亮的（G 15 mag），附近（200 pc）的WD+MS系统，这些系统相距很远，从未相互作用过。首先，研究人员将使用地面档案光变曲线来测量主序星伴星的旋转周期，并通过光谱表征白色矮星，以确定系统的总年龄。总共将开发50-100个校准系统的样本。第二，这项建议将探讨系统的不确定性的能力，白色矮星提供可靠的老年人通过研究同时代对宽WD+WD二进制。最后，它将面对现有的具有经验锚点的恒星自转模型，并为老（4 Gyr）、低质量（0.8太阳质量）恒星开发第一个校准的周期-年龄关系。该奖项反映了NSF的法定使命，并且通过使用基金会的智力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 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.