SIMBAD references

We propose the Gaia spectroscopic observations to be performed over the wavelength interval 8500-8750 Å, with an optimal dispersion of 0.25 Å/pix (or 1000 pixels budget per spectrum) and a 2 pixel PSF. In this paper, on the base of extensive observations as well as synthetic spectra and simulations, we review the spectroscopic performances expected for Gaia: radial and rotational velocities, spectral classification, detection of mass-loss and spectral peculiarities, chemical abundance analysis and reddening estimates from the 8620 Å diffuse interstellar band. Lower dispersion spectra (corresponding to smaller pixel budgets) are considered too.