On the radial abundance gradients of nitrogen and oxygen in the inner
  Galactic disc
  We present optical spectra of nine Galactic H II regions observed with the
10.4 m Gran Telescopio Canarias telescope and located at Galactocentric
distances (RG) from 4 to 8 kpc. The distances of the objects have been revised
using Gaia DR2 parallaxes. We determine the electron temperature for all the
nebulae, which allows a precise computation of their ionic abundances. We have
included published data of an additional sample of Galactic H II regions,
providing a final data set of 42 objects. The shape of the radial gradients of
O/H and N/H is linear and constant, discarding any substantial change of the
slope, at least for RG between 4 and 17 kpc. The small dispersion of the O/H
and N/H values with respect to the computed gradients implies the absence of
significant azimuthal variations of the chemical abundances, at least in the
quadrant covered by our observations. We find an almost flat N/O versus O/H
diagram relation. This result is not observed in other nearby spiral galaxy
except M31. Finally, we compare our computed gradients with those obtained
using far infrared (FIR) spectra. We confirm the significant offset in the N/O
distribution between the optical and FIR observations. Possible explanations
involve ionization correction factors and the strong dependence on density of
the abundance determinations based on FIR lines.
