Discovery of Solar Rieger Periodicities in Another Star

The Rieger periods are solar cycles with a time scale of months, which are present in both flaring activity and sunspot occurrence. These short-term periodicities, tentatively explained by equatorially trapped Rossby-type waves modulating the emergence of magnetic flux at the surface, are considered a peculiar and not yet fully understood solar phenomenon. We chose a stellar system with solar characteristics, UX Arietis, and performed a timing analysis of two 9-year datasets of radio and optical observations. The analysis reveals a 294-day cycle. When the two 9-year datasets are folded with this period, a synchronization of the peak of the optical light curve (i.e., the minimum spot coverage) with the minimum radio flaring activity is observed. This close relationship between two completly independent curves makes it very likely that the 294-day cycle is real. We conclude that the process invoked for the Sun of a periodical emergence of magnetic flux may also be applied to UX Arietis and can explain the cyclic flaring activity triggered by interactions between successive cyclic emergences of magnetic flux.