Stellar population astrophysics (SPA) with the TNG. Characterization of the young open cluster ASCC 123.

Star clusters are key to understand the stellar and Galactic evolution. ASCC 123 is a little-studied, nearby and very sparse open cluster. We performed the first high-resolution spectroscopic study of this cluster in the framework of the SPA (Stellar Population Astrophysics) project with GIARPS at the TNG. We observed 17 stars, five of which turned out to be double-lined binaries. Three of the investigated sources were rejected as members on the basis of astrometry and lithium content. For the remaining single stars we derived the stellar parameters, extinction, radial and projected rotational velocities, and chemical abundances for 21 species with atomic number up to 40. From the analysis of single main-sequence stars we found an average extinction $A_V\simeq 0.13$ mag and a median radial velocity of about $-5.6$ km/s. The average metallicity we found for ASCC 123 is [Fe/H]$\simeq+0.14\pm 0.04$, which is in line with that expected for its Galactocentric distance. The chemical composition is compatible with the Galactic trends in the solar neighborhood within the errors. From the lithium abundance and chromospheric H$\alpha$ emission we found an age similar to that of the Pleiades, which agrees with that inferred from the Hertzsprung-Russell and color-magnitude diagrams.