Variability of Achernar in the Hα line. The Hα line is displayed in the top left panel for the two cases: the emission, Be phase (2006 FEROS spectrum, upper black), and the quiescent, B phase (2003 HARPS spectrum, lower gray, flux-shifted for clarity). Empiric line models are displayed as the red and blue curves, respectively (see text). The three other panels display the time series of the observables derived from the Hα line modeling (from left to right and top to bottom): the E/C ratio, the H_α line RV, and the V/R ratio. At the bottom of each panel, observed emission and quiescent phases are highlighted in red and gray, respectively. The periastron passages at epochs 2008.78 and 2015.81 are marked with green vertical lines. Open blue circles represent data values averaged over large time intervals, highlighted in blue or white in the background.