Chemical gradients in the Milky Way from the RAVE data. I. Dwarf stars
  Aim: We aim at measuring the chemical gradients of the elements Mg, Al, Si,
and Fe along the Galactic radius to provide new constraints on the chemical
evolution models of the Galaxy and Galaxy models such as the Besancon model.
  Methods: We analysed three different samples selected from three independent
datasets: a sample of 19,962 dwarf stars selected from the RAVE database, a
sample of 10,616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS)
dataset, and a mock sample (equivalent to the RAVE sample) created by using the
GALAXIA code, which is based on the Besancon model. We measured the chemical
gradients as functions of the guiding radius (Rg) at different distances from
the Galactic plane reached by the stars along their orbit (Zmax).
  Results: The chemical gradients of the RAVE and GCS samples are negative and
show consistent trends, although they are not equal: at Zmax<0.4 kpc and
4.5<Rg(kpc)<9.5, the iron gradient for the RAVE sample is d[Fe/H]/dRg=-0.065
dex kpc^{-1}, whereas for the GCS sample it is d[Fe/H]/dRg=-0.043 dex kpc^{-1}
with internal errors +-0.002 and +-0.004 dex kpc^{-1}, respectively. The
gradients of the RAVE and GCS samples become flatter at larger Zmax.
Conversely, the mock sample has a positive iron gradient of
d[Fe/H]/dRg=+0.053+-0.003 dex kpc^{-1} at Zmax<0.4 kpc and remains positive at
any Zmax. These positive and unrealistic values originate from the lack of
correlation between metallicity and tangential velocity in the Besancon model.
The discrepancies between the observational samples and the mock sample can be
reduced by i) decreasing the density, ii) decreasing the vertical velocity, and
iii) increasing the metallicity of the thick disc in the Besancon model.
