Seismological insights into solar and stellar magnetic activity cycles

Abstract

The Sun’s magnetic activity cycle varies primarily on a time scale of approximately 11yrs from minimum to maximum and back again. It is well-known that the properties of the Sun’s acoustic oscillations are affected by the near-surface internal magnetic field: Frequencies, damping rates, and powers are all known to vary systematically with solar cycle. Careful observation of these variations, therefore, allows aspects of the Sun’s internal magnetic field to be inferred. However, the Sun is just one star and, with CoROT and Kepler in particular, oscillations can now be observed for thousands of other stars. However, despite many stars showing signs of magnetic activity in their lightcurves, to date, activity cycle-like variations in the properties of asteroseimic oscillations are sparse. Nevertheless, studying the solar-stellar connection advances our understanding of solar and stellar magnetic fields. For example, placing our Sun’s activity cycle in a stellar context suggests that the Sun may be unusual. Conversely, observations of quasi-periodic pulsations in stellar flares suggest the underlying physics of solar and stellar flares are the same.