Magnetic activity variability of nearby bright Sun-like stars by 4 yr intensive Hα line monitoring

We report intensive monitoring of the activity variability in the H alpha line for 10 Sun-like stars using the 1.88 m reflector at Okayama Branch Office, Subaru Telescope, during the last four years (2019-2022). Our aim was to investigate features of the stellar magnetic activity behavior. We correlated the H alpha line variability of each star with the stellar activity levels derived from the Ca II H&K line, suggesting its efficiency as a magnetic activity indicator. In analyzing the H alpha line variation, we observed that some stars exhibited linear or quadratic trends during the observation period. Among several G- and K-type stars expected to have co-existing activity cycles, we confirmed the 2.9 yr short cycle of & varepsilon; Eri (K2V) from the H alpha observations. Additionally, we established upper limits on the H alpha variability of beta Com (G0V) and kappa(1) Cet (G5V) concerning their expected shorter cycles. We also detected the possibility of short-term activity cycles in two F-type stars, beta Vir (F9V; similar to 530 d) and alpha CMi (F5IV-V; similar to 130 d). The cycle in alpha CMi was observed in only one season of our 4 yr observations, suggesting the temporal absence of the cycle period. However, for stars with planets, we did not observe significant magnetic activity variability likely associated with the planetary orbital period. It is speculated that the impact of H alpha variability on radial velocity (RV) measurements may vary with spectral type.