Prominence activity in G dwarfs of the   Persei cluster

We have found evidence for prominence-like circumstellar material in four rapidly rotating G–K dwarfs of the α Persei cluster, He 373, 520, 622 and 699. Our time-series Hα spectra of these stars show transient absorption features similar to those seen in the southern field rapid rotator AB Doradus. The absorption transients have durations of order 1 hr, during which they drift across the rotationally broadened Hα profiles of the stars concerned. This behaviour is consistent with the model developed for AB Dor, in which the absorption transients are produced via scattering of Hα photons in clouds of mainly neutral material trapped in the summits of closed magnetic field structures extending several stellar radii above the surface of the star. We have measured the radial accelerations of several of the most clearly defined transients in the four stars observed. The radial accelerations of these transient absorption features as a function of stellar equatorial rotation speed indicate that, as in AB Dor, the clouds are located preferentially just outside the Keplerian corotation radius.