This paper represents a collective effort to provide an extensive electronic database useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data are discussed here, and the data are made fully available in the AAS CD-ROM Series, Vo. 7. Several empirical stellar libraries are part of this database. They cover the ultraviolet spectral range observed with IUE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but it is mostly complete for types O and M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000 K to 50,000 K, as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this database. We discuss an extensive set of empirical spectra templates covering the wavelength region from 1200 - 9800 A, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic database and to perform a critical comparison between the individual datasets
Using the UVBLUE library of synthetic stellar spectra we have computed a set of mid-UV line and continuum spectroscopic indices. We explore their behavior in terms of the leading stellar parameters (T eff , log g). The overall result is that synthetic indices follow the general trends depicted by those computed from empirical databases. Separately we also examine the index sensitivity to changes in chemical composition, an analysis only feasible under a theoretical approach. In this respect, lines indices Fe i 3000, BL 3096 and Mg i 2852 and the continuum index 2828/2921 are the least sensitive features, an important characteristic to be taken into account for the analyses of integrated spectra of stellar systems. We also quantify the effects of instrumental resolution on the indices and find that indices display variations up to 0.1 mag in the resolution interval between 6-10Å of FWHM. We discuss the extent to which synthetic indices are compatible with indices measured in spectra collected by the International Ultraviolet Explorer (IUE). Five line and continuum indices (Fe i 3000, 2110/2570, 2828/2921, S2850, and S2850L) display a remarkable good correlation with observations. The rest of the indices are either underestimated or overestimated, however, two of them, Mg Wide and BL 3096, display only marginal discrepancies. For 11 indices we give the coefficients to convert synthetic indices to the IUE system. This work represents the first attempt to synthesize mid-UV indices from high resolution theoretical spectra and foresees important applications for the study of the ultraviolet morphology of old stellar aggregates.
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