Magnetic activity variability from H$\alpha$ line intensive monitoring for two F-type stars having a hot-Jupiter, $\tau$ Bootis A and $\upsilon$ Andromedae A

TL;DR

This study monitored H-alpha line variability over four years in two F-type stars with hot Jupiters, revealing a possible 123-day magnetic cycle in $ au$ Boo and long-term trends in $eta$ And, with no clear star-planet magnetic interaction signatures.

Contribution

First intensive 4-year H-alpha monitoring of $ au$ Boo and $eta$ And, identifying magnetic activity cycles and trends, and assessing star-planet magnetic interactions.

Findings

Possible 123-day magnetic cycle in $ au$ Boo.

Long-term H-alpha variability trend in $eta$ And.

No detectable star-planet magnetic interaction signatures.

Abstract

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, during the last four years 2019-2022, in order to investigate their stellar magnetic activity. The 4-year H$\alpha$ line intensity data taken with the 1.88-m reflector at Okayama Branch Office, Subaru Telescope, shows the existence of a possible $\sim$ 123-day magnetic activity cycle of $\tau$ 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 is persisted 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 ($\approx$ 3.31 and 4.62 days, 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.