Magnetic activity variability from Hα line intensive monitoring of two F-type stars with a hot Jupiter, τ Bootis A and υ Andromedae A.

This article presents a four-year spectroscopic study (2019–2022) of the Hα line variability in two F-type stars, τ Bootis A (F7V) and υ Andromedae A (F8V), both hosting hot Jupiter exoplanets, to investigate their stellar magnetic activity. The analysis reveals a significant ∼123-day magnetic activity cycle in τ Boo consistent with previous Ca ii H&K line studies, suggesting a persistent short-term chromospheric cycle likely driven by the stellar intrinsic dynamo. For υ And, a quadratic long-term trend in Hα variability was identified, but no clear magnetic activity cycle period was detected within the observation span. The study found no evidence of star–planet magnetic interaction (SPMI) signatures linked to the planetary orbital periods in either star, setting upper limits on Hα variability induced by such interactions at 1.4% for τ Boo and 1.2% for υ And. These findings support the interpretation that the observed magnetic activity cycles are intrinsic to the stars rather than influenced by their close-in giant planets.