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Description
High-resolution spectroscopy in the near infrared (NIR) is a powerful tool to characterise the physical and chemical properties of cool star atmospheres. The current generation of NIR echelle spectrographs enables the sampling of many spectral features over the full 0.9-2.4um range for a detailed chemical tagging. Within the Stellar Population Astrophysics Large Program at the TNG, we used a high-resolution (R=50000) NIR spectrum of Arcturus acquired with the GIANO-B echelle spectrograph as a laboratory to define and calibrate an optimal line list and new diagnostic tools to derive accurate stellar parameters and chemical abundances. We inspected several hundreds of NIR atomic and molecular lines to derive abundances of 26 different chemical species, including CNO, iron-group, alpha, Z-odd and neutron-capture elements. We then performed a similar analysis in the optical using Arcturus VLT-UVES spectra. By the combined NIR and optical analysis we defined a new thermometer and a new gravitometer for giant stars, based on the comparison of Carbon and Oxygen abundances, respectively, as derived from atomic and molecular lines. We then derived self-consistent stellar parameters and chemical abundances of Arcturus over the full 4800-24500{AA} spectral range and we compared them with previous studies in the literature. We finally discussed a number of problematic lines, which can be affected by deviations from thermal equilibrium and/or chromospheric activity, as traced by the observed variability of HeI at 10830{AA}.
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