Effect of rotational velocity (left panel, increasing from bottom to top) on spectral features at classification resolution. All the stars shown are B3 V standards. At the very high S/N of these spectra, the star with the slowest rotation (v sin i ≈ 35 km s⁻¹) still displays, although very weakly, many of the metallic lines visible at earlier types (or higher luminosities), such as the Si III triplet at λλ 4553, 4568, 4575. The other stars have rotational velocities of ≈ 100, ≈ 125 and ≈ 160 km s⁻¹, respectively. We note the effect on the Si II 4129 Å doublet and the apparent ratio between He I 4471 Å and Mg II 4481 Å. Line identifications after Kilian et al. (1991). The insets show the details of the metallic lines. Right panel shows the same details at the original (R ≈ 85 000) resolution, to appreciate the full extent of the effects. We note the clearly separated Si II doublet at 4129 Å and the triplet structure in He I 4471 Å in the spectrum of HD 178849.