  Several high-resolution spectroscopic studies have provided compelling
observational evidence that open clusters display a decreasing trend of their
barium abundances as a function of the cluster's age. Young clusters (ages~200
Myr) exhibit significant enhancement in the [Ba/Fe] ratios, at variance with
solar-age clusters where the Ba content has been found to be [Ba/Fe]~0 dex.
Different viable solutions have been suggested in the literature, nevertheless,
a conclusive interpretation of such a peculiar trend has not been found.
Interestingly, it is debated whether the other species produced with Ba via
s-process reactions do follow the same trend with age. Pre-main sequence
clusters (~10-50 Myr) show the most extreme behaviour in this respect: their
[Ba/Fe] ratios can reach 0.65 dex, which higher than the solar value by a
factor of four. Crucially, there are no investigations of the other s-process
species for these young stellar populations. In this paper we present, the
first determination of Y, Zr, La, and Ce in clusters IC 2391, IC 2602 and the
Argus association. The main objective of our work is to ascertain whether these
elements reveal the same enhancement as Ba. Our results indicate that, at
variance with Ba, all the other s-process species exhibit a solar scaled
pattern: these clusters confirm a similar trend discovered in the slightly
older local associations (e.g., AB Doradus, Carina Near), where only Ba exhibit
enhanced value with all other s process species being solar. We have discussed
several possible explanations such as e.g., chromospheric effects, departures
from the LTE approximation, or the activation of a different nucleosynthesis
chain. We cannot currently provide the definite answer to this question and
future investigations from theoretical and observational perspectives are
sorely needed.
