  We present a study of departures from Local Thermodynamic Equilibrium (LTE)
in the formation of infra-red lines of Na I, Mg I, Al I, S I, K I and Sr II in
unevolved stars of spectral types F,G,K and metallicities around the solar
metallicity. The purpose of this investigation is to identify lines of these
species that can be safely treated with the LTE approximation in the infra-red
spectra of these types of stars. We employ a set of 40 stars observed with the
GIANO spectrograph at the 3.5 m Telescopio Nazionale Galileo (TNG) and
previously investigated by Caffau et al. We were able to identify many lines
that can be treated in LTE for all the above-mentioned species, except for Sr
II. The latter species can only be studied using three lines in the J-band, but
all three of them display significant departures from LTE. With our small-size,
but high-quality sample we can determine robustly the trends of the abundance
ratios with metallicity, confirming the trends apparent from a sample that is
larger by several orders of magnitude, but of lower quality in terms of
resolution and S/N ratio.
