  We study the spectrophotometric properties of dwarf planet Ceres in the
VIS-IR spectral range by means of hyper-spectral images acquired by the VIR
imaging spectrometer on board the NASA Dawn mission. Disk-resolved observations
with a phase angle within the $7^{\circ}<\alpha<132^{\circ}$ interval were used
to characterize Ceres' phase curve in the 0.465-4.05 $\mu$m spectral range.
Hapke's model was applied to perform the photometric correction of the dataset,
allowing us to produce albedo and color maps of the surface. The $V$-band
magnitude phase function of Ceres was fitted with both the classical linear
model and H-G formalism. The single-scattering albedo and the asymmetry
parameter at 0.55$\mu$m are $w=0.14\pm0.02$ and $\xi=-0.11\pm0.08$,
respectively (two-lobe Henyey-Greenstein phase function); the modeled geometric
albedo is $0.094\pm0.007$; the roughness parameter is
$\bar{\theta}=29^{\circ}\pm6^{\circ}$. Albedo maps indicate small variability
on a global scale with an average reflectance of $0.034 \pm 0.003$. Isolated
areas such as the Occator bright spots, Haulani, and Oxo show an albedo much
higher than average. We measure a significant spectral phase reddening, and the
average spectral slope of Ceres' surface after photometric correction is
$1.1\%k\AA^{-1}$ and $0.85\%k\AA^{-1}$ at VIS and IR wavelengths, respectively.
Broadband color indices are $V-R=0.38\pm0.01$ and $R-I=0.33\pm0.02$. H-G
modeling of the $V$-band magnitude phase curve for $\alpha<30^{\circ}$ gives
$H=3.14\pm0.04$ and $G=0.10\pm0.04$, while the classical linear model provides
$V(1,1,0^{\circ})=3.48\pm0.03$ and $\beta=0.036\pm0.002$. The comparison with
spectrophotometric properties of other minor bodies indicates that Ceres has a
less back-scattering phase function and a slightly higher albedo than comets
and C-type objects. However, the latter represents the closest match in the
usual asteroid taxonomy.
