Collaborative Research: The Coeval Degenerates Survey

K型和M型恒星是银河系中质量最低的恒星，它们是银河系中最丰富、寿命最长的恒星。对于天文学家来说，能够准确地测量他们的年龄是很重要的，这样才能帮助回答这样的问题：从第一批恒星到现在，我们的银河系组装的化石记录是什么？以及“行星系统有多多样化？”冷矮星的寿命足够长，它们记录了整个银河系历史上恒星的形成和化学演化。此外，与围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探测到，但它们所在恒星的年龄要难得多。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自转的工具，以推断古老(40亿岁)K型和M型恒星的准确年龄。他们将通过研究宽广的双星系统来做到这一点，该系统既包含一颗白矮星(WD)，也包含一颗仍在恒星演化主序列(MS)上的恒星。可以在主序星中测量自转，并且可以使用白矮星来推断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。学生们将有机会体验对单个恒星系统的所有权，同时努力为建立星系事件和行星系统演化的时间表这一更广泛的目标做出贡献。学生们将使用从夏威夷山顶上获得的数据，并与波士顿大学的同事互动。恒星随时间旋转是一个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、低质量恒星的已知年龄的经验锚。该项目将利用广泛的WD+MS二进制来提供旋转和年龄校准器。全白矮星年龄是作为死核的冷却时间和前驱系统的氢和氦燃烧寿命的组合。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。这些双星提供了杠杆作用，将周期-年龄关系延伸到银盘的年龄。Gaia DR2已经能够识别1000多个明亮(G 15 MAG)、附近(200个PC)的WD+MS系统，这些系统相隔很远，从来没有相互作用过。首先，研究人员将使用地面档案光曲线来测量主序伴星的自转周期，并对白矮星进行光谱表征，以确定整个系统的年龄。总体而言，它将开发50-100个校准系统的样本。其次，这项提议将通过研究同年代的宽WD+WD双星来探索白矮星提供可靠年龄的能力的系统不确定性。最后，它将用经验锚对抗现有的恒星自转下降模型，并开发出第一个校准的老恒星(4 Gyr)、低质量恒星(0.8太阳质量)的周期-年龄关系。这一奖项反映了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。

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.