Long term disc variability in the Be star o Andromedae

Abstract

We present 18 years of high resolution and S/N Hα spectroscopy of the Be shell star o And, obtained between 1985-2002. Spectra taken during late 1985 show a pure photospheric profile, with disc re-formation commencing in 1986; a process that is found to occur over long timescales (∼103 days). Analysis of the evolution of the properties of the Hα shell profile suggest that the disc kinematics are dominated by rotational motion. It has been shown that disc loss in o And occurs "inside out"; we find that the disc also appears to be rebuilt in a similar manner, with disc material gradually diffusing to larger radii. The long timescale for changes in the bulk properties of the disc, domination of rotational over radial velocities and manner of disc loss and formation are all consistent with the predictions of the viscous decretion disc model for Be star discs.