The complete figure set (20 images) is available in the online journal.
Normalized spectrograms of stars classified as early O-type dwarfs. Wavelength in Å is given on the x-axis, and on the y-axis thick long ticks mark the continuum flux while thin shorter ticks show the 0.8 continuum flux unit level. The spectral absorption features identified as reference are, from left to right by ion, He I+II λ4026, He II λλ4200, 4541, 4686, and He I λ4471 absorption. Emission lines N IV λ4058 and N III λλ4634-40-42 are also identified above star 41. Three Balmer series lines are also identified: H λ3970, Hδ λ4101, and Hγ λ4340.