S stars in the Gaia era: stellar parameters and nucleosynthesis

S stars are s-process and C-enriched (0.5<C/O<1) red giants. Their abundances can be determined thanks to a new grid of MARCS model atmospheres covering their whole parameter range. Detailed abundance determinations in intrinsic S stars (TP-AGB) and extrinsic S stars (binary masqueraders) can provide strong constraints on the s-process nucleosynthesis: in particular, the s-process temperature can be determined using zirconium and niobium abundances, independently of stellar evolution models. Synthetic spectra of dwarf S stars have been computed and will be sought for in spectroscopic survey data, constraining their luminosity thanks to Gaia parallaxes.