Evidence for tidal star-planet interaction in planet-hosting wide binaries

The evolutionary path of single stars is mostly governed by angular momentum loss in the process of magnetic braking. However, if a star has a close-in stellar or planetary companion, tidal interaction may alter the stellar rotation and activity evolution. We explored if exoplanetary systems display observational evidence for star-planet tidal interaction in terms of such altered stellar rotation and activity level. Determining ages and therefore the expected rotational states of single field stars is very challenging. We, therefore, used a sample of planet-hosting stars that are accompanied by wide stellar companions. Without needing knowledge about the absolute ages of the stars, we test for relative differences in activity and rotation of the planet hosts and their co-eval stellar companions, using X-ray observations to measure the stellar activity levels. Employing three different
tidal interaction models, we find that host stars with strongly tidally interacting planets display elevated activity levels compared to their companion stars. We also find that those activity levels and stellar rotation periods follow the usual rotation-activity relationships, implying that the effect is indeed caused by a long-term tidal interaction and not a purely magnetic interaction.