Atomic data for stellar spectroscopy: recent successes and remaining needs

Stellar chemical composition analyses provide vital insights into galactic nucleosynthesis. Atomic line data are critical inputs to stellar abundance computations. Recent lab studies have made significant progress in refining and extending knowledge of transition probabilities, isotopic wavelength shifts, and hyperfine substructure patterns for the absorption lines that are of most interest to stellar spectroscopists. The observable neutron-capture (n-capture) element species (Z > 30) have been scrutinized in lab studies by several groups. For many species the uncertainties in experimental oscillator strengths are ⩽ 10%, which permits detailed assessment of rapid and slow n-capture nucleosynthesis contributions. In this review, extreme examples of r-process-enriched stars in the galactic halo will be shown, which suggest that the description of observable n-capture abundances in these stars is nearly complete. Unfortunately, there are serious remaining concerns about the reliability of observed abundances of lighter elements. In particular, it is not clear that line formation in real stellar atmospheres is being modeled correctly. But for many elements with Z < 30 the atomic transition data are not yet settled. Highlights will be given of some recent large improvements, with suggestions for the most important needs for the near future. (paper)