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

We report the results of intensive monitoring of the variability in the H alpha line for two F-type stars, tau Boo and upsilon And, over the last four years 2019-2022, in order to investigate their stellar magnetic activity. The 4 yr H alpha line intensity data taken with the 1.88 m reflector at the Okayama Branch Office, Subaru Telescope, shows the existence of a possible similar to 123 d magnetic activity cycle for tau Boo. The result of the H alpha variability as another tracer of the magnetic activity on the chromosphere is consistent with previous studies of the Ca ii H & K line and suggests that the magnetic activity cycle persists in tau Boo. For upsilon And, we suggest a quadratic long-term trend in the H alpha variability. Meanwhile, the short-term monitoring shows no significant period corresponding to specific variations likely induced by their hot Jupiter in both cases (asymptotic to 3.31 and 4.62 d, respectively). In this H alpha observation, we could not find any signature of the star-planet magnetic interaction. It is speculated that the detected magnetic activity variability of the two F-type stars is related to the stellar intrinsic dynamo.

Automated summary

We conducted intensive monitoring of the H alpha line variability in two F-type stars, tau Boo and upsilon And, over the last four years (2019-2022) to investigate their stellar magnetic activity. Our results show a possible 123-day magnetic activity cycle in tau Boo, and a quadratic long-term trend in the H alpha variability for upsilon And. Short-term monitoring did not reveal any specific variations induced by their hot Jupiter. This suggests that the magnetic activity variability in these F-type stars is likely driven by intrinsic dynamo processes.