POLLUX: a database of synthetic stellar spectra

Aims. Synthetic spectra are needed to determine fundamental stellar and wind parameters of all types of stars. They are also used for the construction of theoretical spectral libraries helpful for stellar population synthesis. Therefore, a database of theoretical spectra is required to allow rapid and quantitative comparisons to spectroscopic data. We provide such a database offering an unprecedented coverage of the entire Hertzsprung-Russell diagram. Methods. We present the POLLUX database of synthetic stellar spectra. For objects with T(eff) <= 6000 K, MARCS atmosphere models are computed and the program TURBOSPECTRUM provides the synthetic spectra. ATLAS12 models are computed for stars with 7000 K <= T(eff) = 15 000 K. SYNSPEC gives the corresponding spectra. Finally, the code CMFGEN provides atmosphere models for the hottest stars (T(eff) > 25 000 K). Their spectra are computed with CMF_ FLUX. Both high resolution (R > 150 000) optical spectra in the range 3000 to 12 000 angstrom and spectral energy distributions extending from the UV to near-IR ranges are presented. These spectra cover the HR diagram at solar metallicity. Results. We propose a wide variety of synthetic spectra for various types of stars in a format that is compliant with the Virtual Observatory standards. A user-friendly web interface allows an easy selection of spectra and data retrieval. Upcoming developments will include an extension to a large range of metallicities and to the near-IR high resolution spectra, as well as a better coverage of the HR diagram, with the inclusion of models for Wolf-Rayet stars and large datasets for cool stars. The POLLUX database is accessible at http://pollux.graal.univ-montp2.fr/ and through the Virtual Observatory.