Metallicity and absolute magnitude calibrations for F-G type
  main-sequence stars in the Gaia era
  In this study, photometric metallicity and absolute magnitude calibrations
were derived using F-G spectral type main-sequence stars in the Solar
neighbourhood with precise spectroscopic, photometric and Gaia astrometric data
for UBV photometry. The sample consists of 504 main-sequence stars covering the
temperature, surface gravity and colour index intervals $5300<T_{eff} < 7300$
K, $\log g > 4$ (cgs) and $0.3<(B-V)_0<0.8$ mag, respectively. Stars with
relative trigonometric parallax errors $\sigma_{\pi}/\pi\leq0.01$ were
preferred from Gaia DR2 data for the estimation of their $M_V$ absolute
magnitudes. In order to obtain calibrations, $(U-B)_0$ and $(B-V)_0$ colour
indices of stars were preferred and a multi-variable second order equation was
used. Calibrations are valid for main-sequence stars in the metallicity and
absolute magnitude ranges $-2<{\rm [Fe/H]}<0.5$ dex and $2.5<M_V<6$ mag,
respectively. The mean value and standard deviation of the differences between
original and estimated values for the metal abundance and absolute magnitude
are $\langle\Delta {\rm[Fe/H]}\rangle=0.00\pm0.11$ dex and $\langle\Delta M_V
\rangle=0.00\pm0.22$ mag, respectively. In this work, it has been shown that
more precise iron abundance and absolute magnitude values were obtained with
the new calibrations, compared to previous calibrations in the literature.
