Coronal Imaging and X-ray Activity Cycles of an Ultra-fast Rotator AB Dor

By utilizing extensive long-term X-ray observations, we conduct a thorough analysis of the short-term and long-term variability in X-ray emissions from the ultra-fast rotating active star AB Dor. Our analysis reveals that flaring events are common occurance, averaging at approximately 57±23% of the observation time is affected by flares. During flare-free periods, the X-ray light curves exhibit rotational modulation, indicative of the presence of highly active regions within the star's corona. Using a novel light curve inversion code, we undertake coronal imaging to find the structure of these active regions. Our results demonstrate the existence of
two distinct active regions with varying brightness, separated by approximately 180 degrees in longitude. Moreover, these active regions display longitudinal migration and brightness fluctuations over time. Analyzing X-ray data spanning from 1979 to 2022, we identify multiple periodicities. Notably, we observe a cycle with a period of approximately 19.2 years, its first harmonic, suggestive of a Solar-like long-term activity cycle. Additionally, periodicities of approximately 3.6 and 5.4 years are indicative of a flip-flop cycle in X-rays, consistent with previous optical observations.