Abundance Derivations from Solar and Stellar Optical and Ultraviolet Spectra

We show and describe the extent to which spectral calculations match observed high-resolution spectra of standard stars. From such matches, elemental abundance ratios derived for metal-poor stars are now providing a look at the early nucleosynthesis history of the Galaxy. The age and metallicity of extragalactic globular clusters are being constrained by comparing their observed spectra to theoretical stellar spectra that are constructed by coadding spectra of individual stars spanning all types found in old systems.

Problems remain in spectral modelling, however, especially in the UV. Many atomic lines appear which are unidentified in the laboratory and so are missing from the calculations. These affect stars of one-third solar metallicity and higher, namely solar- type stars in the mid-UV, and giants in the near-UV and blue. More metal-poor giants show a different problem: trends in abundances with wavelength, which may arise from improper helium abundance, treatment of convection, or multiphase atmospheres.