Stellar population astrophysics (SPA) with the TNG: The chemical content of the red supergiant population in the Perseus complex

Context. The Perseus complex in the outer disk of the Galaxy hosts a number of clusters and associations of young stars. Gaia is providing a detailed characterization of their kinematic structure and evolutionary properties. Aims. Within the SPA Large Program at the TNG, we secured HARPS-N and GIANO-B high-resolution optical and near-infrared (NIR) spectra of the young red supergiant (RSG) stars in the Perseus complex in order to obtain accurate radial velocities, stellar parameters, and detailed chemical abundances. Methods. We used spectral synthesis to best fit hundreds of atomic and molecular lines in the spectra of the observed 27 RSGs. We obtained accurate estimates of the stellar temperature, gravity, micro- and macroturbulence velocities, and chemical abundances for 25 different elements. We also measured the 12C/13C abundance ratio. Results. Our combined optical and NIR chemical study provides homogeneous half-solar iron with a low dispersion, about solar-scaled abundance ratios for the iron-peak, alpha-, and other light elements, and a low enhancement of Na, K, and neutron-capture elements. This is consistent with the thin-disk chemistry traced by older stellar populations at a similar galactocentric distance of about 10 kpc. We inferred an enhancement of N and a depletion of C and of the 12C/13C isotopic abundance ratio that are consistent with mixing processes in the stellar interiors during the RSG evolution.