The Need for FTS Accuracy in the Analysis of Complex Laboratory and Stellar Spectra

Modern telescopes make it possible to obtain spectra in high resolution (Δ/Δλ ≈ 100000) and high signal-to-noise ratio from 120 nm to 5 μm for hundreds of thousands of stars in our own Galaxy. The high accuracy obtainable in these observations puts very strong qualitative and quantitative requirements on the atomic and molecular data to be used in the analysis. Different types of atomic data are needed, and in this paper we will focus on wavelengths, line identifications and oscillator strengths. We will demonstrate the need for FTS accuracy in wavelengths for direct application to stellar spectra as concerns calibration and line identification. The FTS accuracy is also needed in the analysis of a complex and line-rich spectrum in order to establish the term system, which subsequently also leads to line identifications. We will also discuss the use of FTS-intensities for obtaining experimental branching ratios to compare with observed line absorption in stellar spectra.