Stellar Population Astrophysics (SPA) with the TNG: Stock 2, a
  little-studied open cluster with an eMSTO
  Stock 2 is a little-studied open cluster that shows an extended main-sequence
turnoff (eMSTO). In order to investigate this phenomenon and characterise the
cluster itself we performed high-resolution spectroscopy in the framework of
the Stellar Population Astrophysics (SPA) project. We employed the High
Accuracy Radial velocity Planet Searcher in North hemisphere spectrograph
(HARPS-N) at the Telescopio Nazionale Galileo (TNG). We completed our
observations with additional spectra taken with the Catania Astrophysical
Observatory Spectrograph (CAOS). In total we observed 46 stars (dwarfs and
giants), which represent, by far, the largest sample collected for this cluster
to date. We provide the stellar parameters, extinction, radial and projected
rotational velocities for most of the stars. Chemical abundances for 21 species
with atomic numbers up to 56 have also been derived. We notice a differential
reddening in the cluster field whose average value is 0.27 mag. It seems to be
the main responsible for the observed eMSTO, since it cannot be explained as
the result of different rotational velocities, as found in other clusters. We
estimate an age for Stock 2 of 450$\pm$150 Ma which corresponds to a MSTO
stellar mass of $\approx$2.8 M$_{\odot}$. The cluster mean radial velocity is
around 8.0 km s$^{-1}$. We find a solar-like metallicity for the cluster,
[Fe/H]=$-$0.07$\pm$0.06, compatible with its Galactocentric distance. MS stars
and giants show chemical abundances compatible within the errors, with the
exceptions of Barium and Strontium, which are clearly overabundant in giants,
and Cobalt, which is only marginally overabundant. Finally, Stock 2 presents a
chemical composition fully compatible with that observed in other open clusters
of the Galactic thin disc.
