Pseudo-equivalent width of Hα line vs. spectral type diagram. Measurement errors are 0.5 subtypes for the spectral type and are of the order of 10% with a minimum of 0.1 Å for pEW(Hα) (but scatter due to variability is probably larger than 10%). Dotted, dash-dotted, and dashed lines indicate the boundaries between chromospheric and accretion emission for different authors. Giants, plotted with open squares, have filled Hα lines or in absorption. None of the young stars, plotted with open and filled stars, show accretion emission. The four stars at the accretion boundary discussed in the text are encircled.