Effect of Star Rotation Rate on the Characteristics of Energetic Particle Events

The recent detection of superflares on solar-type stars by the Kepler mission has raised the possibility that they can be associated with energetic coronal mass ejections (CMEs) and energetic particle events (SEPs). These space weather events can impact the habitability of exoplanets around these stars. Here we use the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model to model the time-intensity profile and spectrum of SEPs accelerated at CME-driven shocks from stars of different ages traced by their rotation rates. We consider a solar-like (G-type) star with six different rotation rates varying from 0.5Ω☉ to 3.0Ω☉. In all six cases, a fast CME is launched with the same speed of ∼1500 km s−1; the resulting time-intensity profiles at three locations and energy spectra at five locations at 1 au are obtained. The maximum particle energy at the shock front as a function of r is also shown. Our results suggest that within 0.8 au the maximum particle energy at the shock front increases with the rotation rate of the star. However, event-integrated spectra for the five selected locations along the CME path show complicated patterns. This is because the Parker magnetic field for rapidly rotating stars is more tightly winded. Our results can be used in estimating the radiation environments of terrestrial-type exoplanets around solar-type stars.