Be stars do not mean "Beryllium stars".

Be stars are B-type (early type) stars with emssion (e) lines. Some of them show long-term variablity characterized by brightenings and fadings, and have beem familiar with variable star observers. Typical examples: gamma Cas, X Per, BU Tau etc. Be stars during the bright phases are believed to be experiencing enhanced mass-losses, which then form circumstellar disks which are the main sources of emission lines.