Long-term Doppler imaging of the star XX Trianguli indicates chaotic non-periodic dynamo

Sunspots are the most well-known manifestations of solar magnetic fields and exhibit a range of phenomena related to the interior dynamo. Starspots are the direct analogs of sunspots on other stars but with the big observational restriction that we usually cannot resolve other star’s surfaces. In this paper we employ an indirect surface imaging technique called Doppler imaging and present 99 independent Doppler images of the star XX Trianguli. The star was selected because it had shown a gigantic star spot in a previous study and was thus well suited for a long-term monitoring effort. We combine the Doppler images into a movie visualizing the star’s surface spot evolution for the past 16 years. Stellar-disk photocenter displacements of up to 24 μas, or about 10% of the stellar disk radius, are reconstructed, but do not show the typical solar-like periodic behavior that could be interpreted as an activity cycle. It suggests a mostly chaotic, likely unperiodic, dynamo. These rotation-induced stellar photocenter variations pose an intrinsic limitation for astrometric exoplanet catches.