Time evolution of a Hα EW, Starburst99 SSP. The single-burst model is represented by the black line and continuous star formation by the purple line; both use a standard Salpeter IMF with α = 2.35, M _up = 100  M _☉. Dotted lines represent single-burst solar-metallicity models with different IMFs: red is for α = 3.30, M _up = 100  M _☉, and orange is for α = 2.35, M _up = 30  M _☉. The lifetimes of single stars of different initial masses at solar metallicity according to Padova models are indicated with vertical gray lines.