Coincidence between Rotational Modulations of Coronal and Photospheric Activities on the Saturated Star AB Dor

Abstract The magnetic connection among different layers is observed on the Sun and plays a key role in solar activity. It is also expected to be common on other active stars. However, controversies persist, especially in the case of saturated stars, whose underlying dynamo processes may differ from those of unsaturated stars. Here we demonstrate the existence of such a connection in the ultraactive star AB Dor, a young solar analogue in the saturated regime. Historically, the coronal topology of AB Dor had been extensively studied, however, ambiguities have persisted for a long time. Even the existence of its rotational modulation (RM) is underdebating, let alone its connection to the lower layers of the stellar atmosphere. Through joint analyses of quasi-contemporaneous optical and soft X-ray (SXR) observations over years, we have confirmed the existence of coronal RM in AB Dor, thereby ruling out the interpretation that the saturation is caused by fully covered active regions. The observed coincidence between the RM signals of optical and SXR data indicates a coronal-photospheric connection, supporting the interpretation of a solar-like scenario in saturated stars.