Atomic Data in the 1–5 Micron Region: Present Status

Abstract

We discuss the balance between the potential needs for atomic data and the present status of wavelengths and oscillator strengths for atomic lines in the CRIRES region (1 5 mum). There is a clear distinction between the atomic lines that will appear in absorption in stellar spectra and in emission in nebular spectra. For abundance analyses different classes of lines can be defined on the basis of the energy level structure, either along particular rows or along particular columns in the periodic table. Of particular interest are optically thin lines in spectra of highabundance elements (alkali and alkaline earth elements), for which accurate oscillator strengths can be measured. The resonance lines from the three lowest ionization stages of many rare-earth elements form another group and are of particular interest for analyses of CP stars. Very little atomic data are available for these lines. The nebular spectra contain numerous forbidden lines of potential diagnostic value as well as selectively excited fluorescence lines, some of them acting as astrophysical lasers.