Sample spectra of γ Vel stars in the Hα region, in a sequence of earlier (bottom) to later (middle) spectral types, and including some narrow- and wide-emission stars (top). Colored regions indicate wavelength ranges used to define the indices discussed in the text. Green: continuum region. Orange: Hα line core. Cyan: (inner) line wings. The two dashed vertical lines indicate the Hα line and the [N II] nebular line.