Spectral activity episode of the Be-shell star Pleione in 2013-2018

Pleione is well known as a prototype of a group of similar Be-stars, among the vast diversity of active B type stars. Its transitions between cyclic decades-long periods of having a spectrum with intense emission lines or a spectrum with sharp absorption lines is traced already for more than a century. In the present study we report an episode of Ha emission activity in the spectrum of the Be-shell star Pleione in 2016. It was documented with high resolution spectral observations carried out at VLT (ESO). The outburst of H alpha emission was superimposed onto a gradual spectral changes during the development of a shell spectral phase of Pleione. The H alpha outburst was accompanied by synchronized activity in the H beta line.