EAPSI: Using Seismic Waves to Probe the Structure of Colliding Stars

蓝离散星是最近通过与经过的恒星碰撞或从双星伴星中吸积物质而获得质量的恒星。类似的相互作用创造了许多其他有趣的物体，包括我们用来测量宇宙膨胀的1a型超新星。为了更好地理解这些过程，天文学家需要可靠地测量质量和内部结构的传递和碰撞产物，如蓝离散星。直到最近，使用一种叫做星震学的新技术，这种测量才成为可能。与地震学家利用地震来研究地球内部类似，天文学家利用在恒星内部传播的地震波来探测它们的内部结构。这些波型可以通过恒星亮度的微小变化来探测到。美国宇航局的开普勒任务已经对数千颗恒星的亮度进行了四年的监测，为研究这些地震波提供了开创性的数据集。该项目将研究开普勒观测到的蓝离散星样本，利用它们的地震波模式来确定它们的质量、自转速率和内部结构。这项研究将与新南威尔士大学的丹尼斯·斯特洛博士合作完成，他是世界上为数不多的星震学专家之一。在碰撞和二元传质物理中，两个关键的不确定性是传质效率和角动量演化。结合详细的恒星建模，星震学可以通过提供蓝离散星的精确质量测量来阐明质量传递效率，这是建模者在很大程度上无法获得的限制。一些蓝离散星显示混合p模和g模振荡，允许对核心和包络特性进行单独测量。在这个项目中，测量核心和包络层的旋转速率将阐明在蓝离散星表面增加了多少角动量，以及它是否被传送到恒星核心。这项技术已经为正常恒星的角动量输运提供了许多见解。这个项目将是测量蓝离散星等非标准恒星的这些特性的首批努力之一，并有望为质量传递和碰撞产物的角动量演变提供更多的见解。该奖项由美国国家科学基金会和澳大利亚科学院共同资助，隶属于东亚和太平洋暑期研究所项目，支持一名美国研究生进行暑期研究。

Blue stragglers are stars that have recently gained mass by colliding with a passing star, or accreting material from a binary companion. Similar interactions are responsible for creating many other interesting objects, including the Type 1a supernovae we use to measure the expansion of the universe. To better understand these processes, astronomers need reliable measurements of the mass and internal structure of mass-transfer and collision products like blue stragglers. Such measurements only recently became possible using a new technique called asteroseismology. Similar to seismologists using earthquakes to study the interior of the Earth, astronomers use seismic waves that propagate inside stars to probe their interior structures. These wave patterns can be detected as small variations in a star's brightness. NASA's Kepler mission has monitored the brightness of thousands of stars for four years, providing a groundbreaking data set to study these seismic waves. This project will study a sample of blue stragglers observed by Kepler, using their seismic wave patterns to determine their masses, rotation rates, and internal structures. This research will be done in collaboration with Dr. Dennis Stello at the University of New South Wales, one of a handful of experts on asteroseismology in the world. Two key uncertainties in the physics of collisions and binary mass transfer are the mass transfer efficiency and the angular momentum evolution. In combination with detailed stellar modeling, asteroseismology can shed light on mass transfer efficiency by providing precise mass measurements of blue stragglers, a constraint that has been largely unavailable to modelers. Some blue stragglers display mixed p- and g- mode oscillations, allowing separate measurements of core and envelope properties. For this project, measuring a core and an envelope rotation rate will illuminate how much angular momentum is accreted at the blue straggler surface, and if it is transported down into the stellar core. This technique has already offered many insights into angular momentum transport in normal stars. This project will be one of the first efforts to measure these properties in non-standard stars like blue stragglers, and promises to offer more insight into the angular momentum evolution of mass-transfer and collision products. This award, under the East Asia and Pacific Summer Institutes program, supports summer research by a U.S. graduate student and is jointly funded by NSF and the Australian Academy of Science.