Infrared Abundance Trends in Open Clusters from GIANO-B Observations at TNG

The high-resolution spectrograph GIANO-B installed at the Telescopio Nazionale Galileo (TNG) and operating in the near-infrared wavelength range, has been used to study the chemical composition of 114 giant stars belonging to 41 open clusters. Open clusters are groups of stars that formed together from the same cloud of gas and dust, making them ideal laboratories for tracing the chemical evolution of the Milky Way.

This study presents a homogeneous infrared open-cluster abundance dataset, delivering measurements for 23 chemical elements.

These include α-elements (such as magnesium), which are mainly produced in supernova explosions, odd-Z elements (like sodium), and neutron-capture elements, formed through nuclear reactions involving neutrons inside stars.

Thanks to the high spectral resolution of GIANO-B, astronomers were able to derive stellar abundances with high precision while accounting for non-local thermodynamic equilibrium (non-LTE) effects, which can significantly influence abundance measurements. Observations in the infrared also overcome many of the limitations of optical spectroscopy, allowing accurate measurements of elements such as fluorine and potassium, which are difficult or even impossible to study at visible wavelengths.

The results reveal clear negative Galactic abundance gradients, meaning that elements like iron ([Fe/H]), magnesium ([Mg/H]), and sodium ([Na/H]) decrease with increasing distance from the Galactic centre. These trends confirm that open clusters belong to a chemically homogeneous thin disk, with subtle variations that reflect the processes of stellar nucleosynthesis and the long-term evolution of our Galaxy.

This work highlights the key role of the TNG and its infrared instrumentation in advancing the field of galactic archaeology, by enabling chemical studies of cooler stars and regions of the Milky Way that are heavily obscured by interstellar dust.

Link to the paper.