Unveiling the nature of 12 new low-luminosity Galactic Globular Cluster
  Candidates
  The Galactic globular cluster system is incomplete, especially in the low
latitude regions of the Galactic bulge and disk. We report the physical
characterization of twelve star clusters in the Milky Way, most of which are
explored here for the first time. Our aim is determining their main physical
parameters, such as reddening and extinction, metallicity, age, total
luminosity, mean cluster proper motions (PMs), distances, in order to unveil
their physical nature. We study the clusters using optical and near-infrared
(NIR) datasets. We use the Gaia Early Data Release 3 (EDR3) PMs in order to
perform a PM-decontamination procedure and build final catalogues. We match the
Gaia EDR3 with the VISTA Variables in the V\'ia L\'actea extended (VVVX) survey
and Two Micron All Sky survey (2MASS) in the NIR, in order to construct
complete colour-magnitude diagrams (CMDs) and investigate the clusters
properties. The extinctions are evaluated using existing reddening maps,
spanning $0.09\lesssim A_{Ks}\lesssim 0.86$ mag and $0.89 \lesssim
A_{G}\lesssim 4.72$ mag in the NIR and optical, respectively. We obtain their
heliocentric distances, that range from about 4 to 20 kpc, placing these
clusters at $3\lesssim R_{G}\lesssim 14$ kpc from the Galactic centre. The best
PARSEC isochrone fit yields a metallicity range of $-1.8<$[Fe/H]$<+0.3$ and an
approximative age range of $2<$Age$<14$ Gyr. We find that all clusters have
low-luminosities, with $-6.9<M_{V}<-3.5$ mag. Based on our photometric
analysis, we confirm the OC nature for Kronberger100, while we classify
Patchick125 as a metal-poor GC, Ferrero54 as a metal-rich GC, and ESO92-18 as a
possible old OC or young GC. The classification as GC candidates is also
suggested for Kronberger99, Patchick122, Patchick126, Riddle15, FSR190 and
Gaia2. We also conclude that Kronberger119 and Kronberger143 might be either
old OCs or young GCs.
