In the present paper, we aim to constrain properties of ionisation region in a star from oscillation frequency variation (a so-called glitch) caused by rapid structural variations this very region. particular, seek avoid use calibration based on stellar models thus providing truly independent estimate these properties. These include both helium abundance and other physical quantities that can h...

Context. Protostellar accretion discs have cool, dense midplanes where externally originating ionisation sources such as X–rays or cosmic rays are unable to penetrate. This suggests that for a wide range of radii, MHD turbulence can only be sustained in the surface layers where the ionisation fraction is sufficiently high. A dead zone is expected to exist near the midplane, such that active acc...