发表机构
Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences; HUN-REN CSFK, MTA Centre of Excellence; Eötvös Loránd University; Institute of Physics/IGAM, University of Graz（孔科利天文台，匈牙利研究与教育网络天文学与地球科学研究中心; 匈牙利研究与教育网络科学院研究所，马塔卓越中心; 厄特沃什·罗兰大学; 格拉茨大学物理研究所/IGAM）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过多源数据证实KIC 2852961为密近双星，其内部较差自转驱动的高效磁活动是产生高能超级耀斑的关键，星斑覆盖度与耀斑能量密切相关。
AI 中文摘要
当用高精度空间测光进行连续监测时，红巨星的耀斑活动十分常见，事实上，在红巨星上已观测到被称为“超级耀斑”的能量最强的耀斑。KIC 2852961是开普勒场中产生能量最高耀斑的红巨星，也因大振幅星斑引发的光变而闻名。本研究旨在探究该恒星极端耀斑活动及耀斑能量的成因。研究采用地面光谱测量数据与空间测光数据，使用标准工具对其进行处理，还从Gaia等大型巡天数据库中收集了相关数据。新的径向速度数据证实，该红巨星是密近双星系统的成员，其中潮汐力在控制该双星系统演化中起关键作用。结果表明，潮汐演化已使该系统接近轨道圆化和自转同步，但并未完全限制红巨星的较差自转，而较差自转可使磁发电机极为高效地运作。研究发现，高能（超级）耀斑主要由活跃巨星分量的内部磁活动控制，而非与伴星的相位依赖相互作用。大的星斑引发的自转光变调制表明存在大量星斑，可储存巨量磁能，这为形成极大耀斑提供了条件，证实了大星斑覆盖度与高耀斑能量及/或频率之间的密切关系。此外，较差自转在KIC 2852961的耀斑活动中可能发挥双重作用：既有助于大星斑的形成，又能剪切和扭曲日冕磁场，从而为高能超级耀斑提供动力。
英文摘要
Flare activity in red giants is quite common when continuously monitored with high-precision space photometry. In fact, the most powerful flares, also known as "superflares" have been observed on red giant stars. KIC 2852961 is a red giant star producing the highest-energy flares in the Kepler field, and is also known for its large-amplitude starspot-induced light variations. Our goal is to find out what causes the extreme flare activity and flare energies in this star. For our investigations, we use ground-based spectroscopic measurements and space photometric data, which we process using standard tools. We also collect relevant data from databases of large surveys such as Gaia. Our new radial velocity data confirm that the red giant star is part of a close binary system, in which tidal forces play a crucial role in controlling the evolution of the binary system. Our results show that tidal evolution has driven the system close to orbital circularization and rotational synchronization, but it did not completely constrain the differential rotation of the red giant, in which the magnetic dynamo can operate extremely efficiently. We find that high-energy (super)flares are primarily controlled by the internal magnetic activity of the active giant component, rather than phase-dependent interactions with the secondary star. The large spot-induced rotational light modulations indicate extensive starspots that can store enormous amounts of magnetic energy. This provides the conditions for the formation of extremely large flares, confirming the close relationship between large spot coverage and high flare energies and/or frequency. Behind all this, differential rotation may play a dual role in the flare activity of KIC 2852961: it contributes both to the formation of large starspots and to the shearing and twisting of coronal magnetic fields that can power energetic superflares.
Comments20 pages, 15 figures, submitted to Astronomy and Astrophysics (after revision in accordance with the Referee's requests)
