脉动白矮星的搜寻和精确星震学研究

White dwarf stars are the late stage of evolution of the moderate- and low- mass stars which account for more than 98% of the total number of stars in the Galaxy. The investigation of white dwarf stars is important to not only verifying and developing the theory of stellar structure and evolution at the late stage of stellar evolution, but also improving our understandings to the formation, structure and evolution of the Milky Way. Asteroseismology is the only and powerful tool to explore the internal structures and physics processes of stars, while searching for new pulsating white dwarfs with different properties provides samples for both asteroseismological and statistical study. We plan to determine candidates located in the instability strips of pulsating white dwarfs by making use of the large amount of data of the LAMOST surveys, the South Galactic Cap u-band Sky Survey and the SDSS surveys. With time-series photometric observations, the candidates will be checked to search for new pulsating white dwarf stars. We shall also organize long-term international observation campaigns for a number of pulsating white dwarf stars to detect the multiple pulsation frequencies. A series of theoretical models will be constructed, whose theoretical frequencies will be compared with the observational frequencies to derive precisely the parameters of the target stars with asteroseismology. The long-term variations of the pulsation frequencies and the reasons will be probed. Core crystallization effect is going to be tested for the ultramassive white dwarfs. The planned research on these cutting-edge scientific questions in the field will definitely lead to deepen understandings to the internal structure and evolutionary law of white dwarf stars as a very important type of stars.

白矮星是约占银河系恒星总数98%的中小质量恒星的演化晚期形态，其研究不仅对演化晚期的恒星结构和演化理论的检验和发展具有重要意义，而且对银河系的形成、结构和演化具有重要的参考价值。星震学是探测恒星内部结构和物理过程的强有力工具，而具有不同性质的脉动白矮星的搜寻为星震学研究提供样本和统计基础。本项目计划利用LAMOST、南银冠u波段和SDSS巡天的海量数据筛选位于白矮星脉动不稳定带内的候选体样本，并进行时序测光观测，以搜寻新的脉动白矮星；针对一批重要的脉动白矮星进行国际多台址联合观测，探测其多重脉动频率，并结合理论模型，利用星震学方法精确测定脉动白矮星的多项参数，验证大质量白矮星内核结晶理论；监测脉动白矮星频率的长期变化并探究其原因，探测可能的行星系统。对该领域这些国际前沿性科学问题的研究，将极大地加深人们对白矮星这类重要恒星的内部结构和演化规律的认识。

本项目执行期间，开展了利用时序测光观测搜寻新的脉动白矮星，以及组织国际联测并结合理论模型对脉动白矮星的精确星震学研究。一方面，基于LAMOST等巡天项目发现的白矮星样本和确定的恒星大气参数，筛选候选体后利用时序测光观测发现了5颗新的脉动白矮星，排除了另外5颗候选体，并在两个拥有脉动变星的食双星系统中发现两颗极端小质量白矮星子星并确定其物理参数。这些成果为深入的星震学研究提供了新的重要的研究目标，并为白矮星脉动性质的统计分析增添了新的样本。另一方面，对3颗脉动白矮星进行了多台站时序测光观测。经过数据处理和分析，得出了恒星脉动频率，并利用多重频率分裂测量了3颗目标星的自转周期。通过与理论模型本征脉动频率的拟合，得出了恒星的有效温度、质量、氢壳层和氦壳层质量等物理参数，发现WD0246+326是一颗质量为0.98±0.01M⊙的大质量白矮星，其内核有可能处于结晶状态；G132-12是一颗靠近不稳定带蓝边缘的单频DA型脉动白矮星，是潜在的稳定白矮星星钟；基于GD133的精确星震学研究得出的恒星质量的误差为0.002太阳质量，达到恒星质量测量的最精确值之一，为后续搜寻其可能的行星系统奠定了基础。此外，对一批其他类型脉动变星和食双星分别开展了星震学和双星性质研究，取得了相应的研究成果。