  The detailed chemical composition of stars is important in many astrophysical
fields, among which the characterisation of exoplanetary systems. Previous
studies seem to indicate an anomalous chemical pattern of the youngest stellar
population in the solar vicinity with a sub-solar metal content. This can
influence various observational relations linking the properties of exoplanets
to the characteristics of the host stars, for example the giant
planet-metallicity relation. In this framework, we aim to expand our knowledge
of the chemical composition of intermediate-age stars and understand whether
these peculiarities are real or related to spectroscopic analysis techniques.
We analysed high-resolution optical and near-infrared GIARPS spectra of
intermediate-age stars (< 700Myr). To overcome issues related to the young ages
of the stars, we applied a new spectroscopic method that uses titanium lines to
derive the atmospheric parameters, in particular surface gravities and
microturbulence velocity parameter. We also derived abundances of 14 different
atomic species. The lack of systematic trends between elemental abundances and
effective temperatures validates our method. However, we observed that the
coolest (<5400 K) stars in the sample, display higher abundances for the Cr II,
and for high-excitation potential C I lines. We found a positive correlation
between the higher abundances measured of C I and Cr II and the activity index
logR$_{HK}$. Instead, we found no correlations between the C abundances
obtained from CH molecular band at 4300\AA, and both effective temperatures and
activity. Thus, we suggest that these are better estimates for C abundances in
young and cool stars. Finally, we found an indication of an increasing
abundance ratio [X/H] with the condensation temperature for HD167389,
indicating possible episodes of planet engulfment.
