Chemical gradients in the Milky Way from the RAVE data. II. Giant stars
  We provide new constraints on the chemo-dynamical models of the Milky Way by
measuring the radial and vertical chemical gradients for the elements Mg, Al,
Si, Ti, and Fe in the Galactic disc and the gradient variations as a function
of the distance from the Galactic plane ($Z$). We selected a sample of giant
stars from the RAVE database using the gravity criterium 1.7$<$log g$<$2.8. We
created a RAVE mock sample with the Galaxia code based on the Besan\c con model
and selected a corresponding mock sample to compare the model with the observed
data. We measured the radial gradients and the vertical gradients as a function
of the distance from the Galactic plane $Z$ to study their variation across the
Galactic disc. The RAVE sample exhibits a negative radial gradient of
$d[Fe/H]/dR=-0.054$ dex kpc$^{-1}$ close to the Galactic plane ($|Z|<0.4$ kpc)
that becomes flatter for larger $|Z|$. Other elements follow the same trend
although with some variations from element to element. The mock sample has
radial gradients in fair agreement with the observed data. The variation of the
gradients with $Z$ shows that the Fe radial gradient of the RAVE sample has
little change in the range $|Z|\lesssim0.6$ kpc and then flattens. The iron
vertical gradient of the RAVE sample is slightly negative close to the Galactic
plane and steepens with $|Z|$. The mock sample exhibits an iron vertical
gradient that is always steeper than the RAVE sample. The mock sample also
shows an excess of metal-poor stars in the [Fe/H] distributions with respect to
the observed data. These discrepancies can be reduced by decreasing the number
of thick disc stars and increasing their average metallicity in the Besan\c con
model.
