Abstract We present a brief review of observational results contributing to modern ideas on the evolution of stellar activity. Basic laws, derived for both rotation-age and activity-rotation relationships, allow us to trace how the activity of low-mass stars changes with age during their stay on the main sequence. We focus on the evaluation of the activity properties of stars that could be analogs of the young Sun. Our study includes joint consideration of different tracers of activity, rotation and magnetic fields of Sun-like stars of various ages. We identify rotation periods, when the saturated regime of activity changes to the unsaturated mode, when the solar-type activity is formed: for G- and K-type stars, they are 1.1 and 3.3 days, respectively. This corresponds to an age interval of about 0 . 2 − 0 . 6 Gyr, when regular sunspot cycle began to be established on the early Sun. We discuss properties of the coronal and chromospheric activity in young Suns. Our evaluation of the EUV-fluxes in the spectral range of 1350 − 1750 A shows that the far-UV radiation of the early Sun was a factor of 7 times more intense than that of the present-day Sun, and twice higher when the regular sunspot cycle was established. For the young Sun, we can estimate the possible mass loss rate associated with quasi-steady outflow as 1 0 − 12 M ⊙ /yr. The results of observations of the largest flares on solar-type stars are also discussed, leading to conclusion that the most powerful phenomena occur on the fast-rotating stars in the saturated activity regime. Our estimate of the stellar magnetic fields makes it possible to evaluate the maximal possible flare energy. This could help us better understand the origin of extreme events on the Sun in the past.

中文翻译：

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太阳恒星活动的演变

摘要 我们简要回顾了对恒星活动演化的现代观点做出贡献的观测结果。由自转-年龄和活动-自转关系导出的基本定律使我们能够追踪低质量恒星在它们停留在主序带期间的活动如何随年龄变化。我们专注于评估可能类似于年轻太阳的恒星的活动特性。我们的研究包括对不同年龄的类太阳恒星的活动、旋转和磁场的不同示踪剂的联合考虑。我们确定旋转周期，当活动的饱和状态变为不饱和模式时，当太阳型活动形成时：对于 G 型和 K 型恒星，它们分别为 1.1 和 3.3 天。这对应于大约 0 的年龄间隔。2 - 0 。6 吉尔，当太阳早期的太阳黑子周期开始建立时。我们讨论了年轻太阳的日冕和色球活动的特性。我们对 1350 - 1750 A 光谱范围内的 EUV 通量的评估表明，早期太阳的远紫外线辐射强度是现代太阳的 7 倍，而常规太阳的远紫外线辐射强度则高两倍。太阳黑子周期成立。对于年轻的太阳，我们可以估计与准稳态流出相关的可能的质量损失率为 1 0 − 12 M ⊙ /yr。还讨论了对太阳型恒星最大耀斑的观测结果，得出最强大的现象发生在饱和活动状态下的快速旋转恒星上的结论。我们对恒星磁场的估计使得评估最大可能的耀斑能量成为可能。