  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 Programme 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 macro turbulence
velocities and chemical abundances for 25 different elements. We also measured
the $^{12}$C/$^{13}$C abundance ratio. Results. Our combined optical and NIR
chemical study provides homogeneous half-solar iron with a small dispersion,
about solar-scaled abundance ratios for the iron-peak, alpha and other light
elements and a small enhancement of Na, K and neutron-capture elements,
consistent with the thin disk chemistry traced by older stellar populations at
a similar Galactocentric distance of about 10 kpc. We inferred enhancement of
N, depletion of C and of the $^{12}$C/$^{13}$C isotopic abundance ratio,
consistent with mixing processes in the stellar interiors during the RSG
evolution.
