Abstract
The author first describes the basis of spectrum synthesis calculations where line lists with atomic and molecular constants are introduced. The accuracy of present-day available model atmospheres is also discussed. The application of synthetic spectra to reproduce the spectra of different objects is then described: the derivation of elemental and isotopic ratios is shown, including a discussion on results for the carbon, nitrogen and oxygen elements. The study of de-veiled spectra of T Tauri stars is described, where molecular bands can be used to check stellar parameters. A grid of 700 synthetic spectra together with reference stars, used through a perturbation method to study stellar populations is described. Finally the reproduction of strong features in composite spectra, and in particular, the Mg I triplet lines, the Ca II triplet lines, and TiO bands in metal-rich globular clusters and SO/E galaxies is given.
