  We present the calibration of the [$\alpha$/Fe] element in terms of the
ultra-violet excess for 469 dwarf stars with $0.325<(B-V)_0 \leq 0.775$ mag
corresponding the spectral type range F0-K2. The star sample is separated into
nine sub-samples with equal range in $(B-V)_0$ colour, $\Delta(B-V)_0=0.05$
mag, and a third degree polynomial is fitted to each dataset. Our calibrations
provide [$\alpha$/Fe] elements in the range [0.0, 0.4]. We applied the
procedure to two sets of field stars and two sets of clusters. The mean and the
corresponding standard deviation of the residuals for 43 field stars taken from
the Hypatia catalogue are [$\alpha$/Fe]=-0.090 and $\sigma =0.102$ dex, while
for the 39 ones taken from the same catalogue of stars used in the calibration
are [$\alpha$/Fe]=-0.009 and $\sigma = 0.079$ dex, respectively. We showed that
the differences between the mean of the residuals and standard deviations for
two sets of clusters ([$\alpha$/Fe]=0.073 and $\sigma = 0.91$ dex;
[$\alpha$/Fe]=-0.012 and $\sigma = 0.053$ dex) originate from the $(B-V)_0$ and
$(U-B)_0$ colour indices of the clusters which are taken from different
sources. The differences between the original [$\alpha$/Fe] elements and the
estimated ones (the residuals) are compatible with the uncertainties in the
literature. Also, there is a good agreement between the distribution of the
synthetic alpha elements versus ultra-violet excesses and the ones obtained via
our calibrations.
