Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler

Abstract

Stellar activity cycles have been found on many stars through different methods. Although in debate, an empirical relation has been found where a period of stellar activity cycle P cyc is positively correlated with rotation period P rot along some segregated branches. In this work, we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible origins. After a rigorous selection, we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability (amplitude of rotational modulation) periods and rotation periods were derived. Due to the 4-year duration of the Kepler mission, our targets are located in the region where the cycle periods are longer than ∼1 yr and shorter than ∼2.5 yr. However, all of our targets exhibit clear and notable quasi-periodic variations in variability, yet we cannot confirm any linear trends that were predicted by previous research independently. This may suggest that in the Kepler realm of the P cyc–P rot diagram, these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.