White Dwarf Stars Under the Influence of Planets

白矮星代表了宇宙中97%的恒星的最终演化状态，包括我们的太阳。在发现它们后的一个世纪里，它们提供了对基本物理、恒星演化和相互作用以及银河系恒星种群年龄的洞察。过去十年的观测还表明，25%-50%的白矮星拥有残存的行星系统，最近在它们的大气中存在吸积的金属就是明证。在这些被污染的白矮星中，有一小部分是由被破坏的系外行星碎片组成的宿主气体和尘埃盘，其中一些显示出与行星残留物正在进行的电磁相互作用的证据。这些发现提供了新的可能性，增强了我们对银河系元素历史、系外系的性质以及行星对恒星演化的影响的理解。北卡罗来纳大学教堂山分校的一个研究小组将对银河系盖亚地图上最冷的金属污染(DZ或DAZ型)白矮星进行光谱调查。他们将利用他们的结果来解决从主序恒星推断的锂丰度与大爆炸核合成预期之间的众所周知的冲突。这项工作将发现新的白矮星，可以解决这一“宇宙锂问题”，并通过与太阳系陨石的古代类比来探索早期银河系元素的丰度。研究人员将与他们的教育和外展合作伙伴莫尔黑德天文馆和科学中心(MPSC)合作，为公众带来系外科学的兴奋，为“发射实验室”开发一个挑战，该实验室是MPSC的新的交互式修补空间，让参观者探索从当前研究中得出的问题。目前，银河系的元素历史主要是通过主序恒星的光球层来测量的，但对于锂来说，这可能特别不可靠，因为锂的消耗温度相对较低。在太阳系中，行星、小行星，尤其是陨石，为推断太阳星云的原始组成提供了另一种方法。到目前为止，这种方法还不适用于我们的太阳系之外，但受污染的白矮星提供了一条将其扩展到其他银河系和纪元的途径。研究人员还将研究DZS和DAS，它们正在通过可观测的圆盘积极地吸积行星碎片，这些圆盘通常显示出与椭圆气体圆盘进动相关的多普勒展宽的钙发射。该项目包括进一步发现和监测碎片盘，以帮助了解遗迹系外行星系统的形成、演化和动力学。最后，研究人员将研究白矮星与残存行星电磁相互作用的证据，并探索行星和合并对白矮星演化的影响。这一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。

White dwarf stars represent the final evolutionary state for ~97% of the stars in the Universe, including our own Sun. In the century since their discovery they have provided insight into fundamental physics, stellar evolution and interactions, and the ages of Galactic stellar populations. Observations across the past decade also suggest that 25-50% of white dwarfs host remnant planetary systems, as evidenced by the presence of recently accreted metals in their atmospheres. A small fraction of these polluted white dwarfs host gas and dust disks consisting of debris from disrupted exoplanetesimals, and some show evidence for ongoing electromagnetic interaction with a planetary remnant. These discoveries provide new possibilities to enhance our understanding of the elemental history of our Galaxy, the nature of exoplanetary systems, and the influence of planets on stellar evolution. A research team at the University of North Carolina at Chapel Hill will conduct a spectroscopic survey of the coolest metal-polluted (types DZ or DAZ) white dwarfs from the Gaia map of the Milky Way Galaxy. They will use their results to address a well-known conflict between lithium abundances as inferred from main-sequence stars and the expectations of Big Bang nucleosynthesis. The work will find new white dwarfs that can address this “Cosmological Lithium Problem” and explore early Galactic element abundances via ancient analogs to Solar System meteorites. In collaboration with their education and outreach partner Morehead Planetarium and Science Center (MPSC), the investigators will bring the excitement of exoplanetary science to the public by developing a challenge for the "Launch Lab," MPSC's new interactive tinkering space that lets visitors explore problems drawn from current research.The Galaxy’s elemental history is currently measured primarily from the photospheres of main-sequence stars, but this can be especially unreliable for lithium, which is consumed at relatively low temperatures. In the Solar System, planets, asteroids, and especially meteorites offer an alternate means of inferring the primordial composition of the solar nebula. This method has not hitherto been applicable outside our Solar System, but polluted white dwarfs offer a path to extend it to other Galactic systems and epochs. The researchers will also study DZs and DAZs that are actively accreting planetary debris via observable disks, which typically show Doppler-broadened calcium emission associated with the precession of an elliptical gas disk. The project includes further discovery and monitoring of debris disks to help understand the formation, evolution, and dynamics of relic exoplanetary systems. Finally, the researchers will study white dwarfs with evidence for electromagnetic interaction with a remnant planet, and explore the effects of planets and mergers on the evolution of white dwarfs.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.