Blue region traditionally used for OB-star classification (left) and red region (right) including Hα for the targets observed with X-shooter. The rest wavelengths of the fitted spectral lines for each star are indicated by the vertical dashed lines. The spectra include prominent diffuse interstellar bands (DIBs). The spectra have been clipped and smoothed to remove the residuals of the sky subtraction. B163, B331, and B337 are not included because they are severely extincted in this wavelength range.