Towards a high resolution view of infrared line formation

We have used H band spectra from IGRINS (R ~45000) of 34 K giants to investigate the limits of infrared spectroscopy. The principal question is: to what extent do abundances derived from infrared spectra agree with optical values, and which aspects of the line formation cause eventual discrepancies? The aspects investigated in this study are: macroturbulence determination; astrophysical line strengths; NLTE corrections; and hyperfine structure.

Our infrared abundances are benchmarked against results from high resolution optical spectra of the same stars (Jönsson, H., et al., in prep.). Stellar parameters derived from the optical spectra are used in this study, as techniques for determining them from infrared spectra are still being developed.

Preliminary results show good agreement between infrared and optical results for a number of elements. The method of determining macroturbulence has shown to be a decisive factor in supersolar abundance trends. A method that accounts for fine and hyperfine structure lines when astrophysically measuring spectral line strength has been developed, along with showing the importance of adjusting lines without lab measurements. NLTE corrections from Amarsi, A., et al. (2020) have been evaluated and shown to generally improve the agreement between optical and infrared results. Accounting for hyperfine structure lines has shown to be essential for elements with strong lines.