Abstract

Based on photometric observations published in the literature, the manifestations of the activity of the K2 V dwarf HD 166620 were studied. The obtained results are compared with the results of the analysis of the chromospheric activity of the star. HD 166620 is entering in a long magnetic minimum and may be the first reliable candidate for objects that are at a minimum of activity similar to the Maunder minimum (MM) of the Sun. Studies of changes in the magnetic activity of the star were carried out based on the values of the S-index (1885 measurements in the observation interval for 53.6 years), obtained mainly before its entry into the MM phase, and on photometric measurements of the brightness in the b and y filters covering 17 seasons from 1993 to 2020 obtained with the automatic APT telescope (MM phase and its beginning). It has been established that the Kamogata Wide-field Survey observation data combined into a single array in the filters B, V, and Ic (about 1400 measurements) convincingly demonstrates the long-term variability of the HD 166620 brightness in the phase of the probable MM state. At the same time, the observations of the Kamogata Wide-field Survey fill the gap in the photometric data of the APT automatic telescope well. The value of the cycle (about 4000 days) is comparable to the duration of observations; if it is refined according to the data of a larger time interval, it is possible that it will correspond more to the value found from the data on chromospheric activity. The main results of the work should include the cyclic long-term changes in the activity of the star detected by us during the beginning of the MM phase. The question of clarifying the value of the rotation period HD 166620 remains open. There were no significant peaks corresponding to the value \(P{{ = 45.06}^{d}}\) days, previously accepted as the period of rotation of the star, on almost all the power spectra constructed by us. It is noted that further observations are required to establish the full duration of the minimum phase of the star’s activity.

中文翻译：

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HD 166620 的长磁极小值——可能是蒙德极小期模拟的开始

摘要

根据文献中发表的光度观测结果，研究了K2 V矮星HD 166620的活动表现。将获得的结果与恒星色球活动的分析结果进行比较。HD 166620 正在进入一个长期的磁极小期，可能是第一个可靠的候选天体，其活动最低期类似于太阳的蒙德极小值 (MM)。对恒星磁活动变化的研究是根据主要在进入 MM 阶段之前获得的 S 指数值（53.6 年观测间隔中的 1885 次测量值）以及恒星的光度测量值进行的。b和y的亮度使用自动APT望远镜（MM阶段及其开始）获得的涵盖1993年至2020年17个季节的滤光片。已经确定 Kamogata Wide-field Survey 观测数据在滤波器 B、V和Ic中组合成单个阵列（约 1400 次测量）令人信服地证明了 HD 166620 亮度在可能的 MM 状态相位中的长期变化。同时，鸭方广域巡天观测结果很好地填补了APT自动望远镜光度数据的空白。周期值（约 4000 天）与观察持续时间相当；如果根据更大时间间隔的数据进行细化，它可能会更符合从色球活动数据中找到的值。这项工作的主要成果应该包括我们在MM阶段开始时探测到的恒星活动的周期性长期变化。澄清旋转周期 HD 166620 的值的问题仍然悬而未决。没有与该值对应的显着峰\(P{{ = 45.06}^{d}}\)天，之前在我们构建的几乎所有功率谱上都被认为是恒星的自转周期。值得注意的是，需要进一步的观测来确定恒星活动最小阶段的完整持续时间。