分离白矮星双星中红矮星活动性的观测研究

Red dwarfs are the most populous stellar objects in the universe and have very strong activities. However, despite the fact that they are the most common stars, their physical properties are poorly understood. A serious problem in this field is the significant discrepancy between the theoretical and observational mass–radius relations, i.e. the observed radius is about 10 per cent larger than that computed from theoretical models. It was realized that this discrepancy could attribute to the strong magnetic activities (for example, the high spot coverage on the photosphere) of the components in short-period red-dwarf eclipsing binaries. Therefore, the study of the activities of red dwarfs becomes the key issue to solve this problem. The detached white dwarf binary is composed of one white dwarf and one red dwarf. Its white dwarf has no solar-like activity, so except the eclipse variation, the light variation of the detached white dwarf binary all comes from its red dwarf component. This makes the detached white dwarf binary an excellent laboratory to study the activity of the red dwarf. In this project, we will choose the eclipsing detached white dwarf binaries as the targets, using available middle and small diameter telescopes to monitor them, obtaining the long term light variation and the flare events by combining with the existing data. According to the analysis of the complete light curves, we will derive their structures，evolution states and basic physical parameters, such as inclinations and relative radii. Together with other data, we will estimate the flare rate and evaluate the relation of the flare rate,the orbital period and the change of the light variation, providing the observational evidences for high dark-spot coverage on red dwarfs based on the physical parameters, light variations and flare events. And then solve the mass–radius problem in this field.

红矮星是宇宙中数目最多的天体，同时也是活动性最强的恒星。然而，人们对这种数目最多的天体的了解却不多，恒星结构与演化理论在该领域面临“质-径”关系难题，即实测的半径要比理论预言的大10%左右。由于人们意识到这种偏差可能是由于红矮星很强的活动性（如光球表面大面积黑子覆盖等）引起，红矮星活动性的研究也就成为解决这一难题的关键。在由一颗白矮星和一颗红矮星组成的分离白矮星双星中，由于白矮星不具有类太阳活动，系统光变除掩食外都来源于红矮星，所以他们是研究红矮星活动规律的绝佳场所。本项目将以掩食的分离白矮星双星系统为研究对象，对分离白矮星双星系统进行长期的监测，并结合已有资料，获取耀斑爆发和长期光变信号。求解双星的基本物理参量，分析双星的结构和演化状态。测定耀斑爆发率及其与光变变化以及轨道周期等的相关性，结合光度变化和双星基本物理参量给出红矮星表面大面积黑子覆盖的证据，解决恒星结构与演化理论面临的难题。

宇宙中 80%以上的恒星是红矮星,然而人们对这种数目最多的恒星却了解得很少。目前这一研究领域存在的未解决难题是：恒星结构演化理论预言的半径要比实测的半径小10%左右，即红矮星的质-径关系难题。人们虽然意识到导致这一差别的原因可能是由于测定恒星半径的掩食密近双星的子星有很强的磁活动引起，但没有足够的观测上的证据支持。.本项目的主要研究内容就是以掩食的分离白矮星双星为研究对象，试图从观测上找出解释红矮星的质-径关系难题的证据。通过对一批掩食的分离白矮星双星进行观测研究，我们在白矮星双星J162117中发现了一种新型的恒星爆发，这种爆发与分离白矮星双星中红矮星伴星的磁活动密切相关。其爆发期间主食变深，次食变浅，爆发振幅极低。当双星处于宁静态时，该系统光变曲线的O’Connell效应明显，当爆发时，O’Connell效应消失。由于白矮星不具有类太阳活动，说明活动来源于双星中的红矮星，由于红矮星表面有大量黑子的覆盖，其光变曲线展现出明显的O’Connell效应。黑子覆盖会导致子星膨胀，半径变大，当半径大到充满洛希瓣时，物质转移开始，物质被吸积到白矮星表面，从而引起爆发，黑子消失，光变曲线中的O’Connell随之消失。这给出了黑子覆盖导致子星膨胀的观测证据，解释了红矮星的质径关系难题。除此之外，我们还在不同类型的具有红矮星子星的双星中发现了不同程度的黑子覆盖率，并发现红矮星的活动性可能与伴星温度有关。