2000PASP..112.1446W

High signal-to-noise, optical digital classification spectrograms of three northern very early O supergiants and four late O supergiants with CNO anomalies are illustrated and discussed. Several of these exceptional objects either are the prototypes of their classes, originally discovered photographically, or are unique representatives of them in the northern hemisphere. The full blue-violet and yellow-red spectrum of the extreme ON supergiant BD +36°4063, discovered by G. Mathys with limited wavelength coverage, is shown for the first time. Extensive line identifications are provided, and the high quality of these data reveals numerous new absorption and emission features corresponding either to the high ionization in the case of the very early objects, or to the chemical abundance anomalies in the later ones. These data provide standards for digital classification of related objects in the north and guidance for subsequent astrophysical analyses with higher spectral resolution.