First neighbour fit of synthetic spectra to the observed spectra for the four spectra of Vega, observed at different epochs, retrieved from PolarBase and SOPHIE databases. Observed spectra are shown in black and the synthetic spectra are shown in red. Part a) represents the overall spectrum, whereas part b) indicates the region sensitive to [Fe/H] and vsini. The wavelengths are in Å. Spectra were offset by arbitrary amounts.