11institutetext: Departamento de Ciencias Físicas, Facultad de Ciencias
Exactas, Universidad Andres Bello, Fernández Concha 700, Las Condes, Santiago,
Chile 22institutetext: Vatican Observatory, Vatican City State, V-00120, Italy
33institutetext: Deepskyhunters Collaboration, e-mail:
<EMAIL_ADDRESS>44institutetext: EBG MedAustron GmbH, Marie-Curie-
Strasse 5, A-2700 Wiener Neustadt, Austria 55institutetext: Centro de
Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta,
Chile 66institutetext: Millennium Institute of Astrophysics , Nuncio Monseñor
Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile 77institutetext:
Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610,
Antofagasta, Chile 88institutetext: Departamento de Física, Universidade
Federal de Santa Catarina, Trindade 88040-900, Florianópolis, SC, Brazil
99institutetext: INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello
16, 80131 Napoli, Italy 1010institutetext: North Optics Instrumentos
Científicos, La Serena, Chile

# Unveiling the nature of 12 new low-luminosity Galactic Globular Cluster
Candidates

E. R. Garro 11 D. Minniti 1122 B. Alessi 33 D. Patchick 33 M. Kronberger 44 J.
Alonso-García 5566 J. G. Fernández-Trincado 77 M. Gómez 11 M. Hempel 11 J. B.
Pullen 11 R.K. Saito 88 V. Ripepi 99 R. Zelada Bacigalupo 1010

(Received XXX; Accepted YYY)

###### Abstract

Context. 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.

Aims. Our primary 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 the physical nature of
these clusters.

Methods. We study the clusters using optical and near-infrared (NIR) datasets.
In particular, we use the Gaia Early Data Release 3 (EDR3) PMs in order to
perform a PM-decontamination procedure and build final catalogues with
probable-members. We match the Gaia EDR3 with the VISTA Variables in the Vía
Láctea extended (VVVX) survey and Two Micron All Sky survey (2MASS) in the
NIR, in order to construct complete NIR and optical colour-magnitude diagrams
(CMDs) and investigate the clusters properties.

Results. The extinctions are evaluated using existing reddening maps. We find
ranges 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. Adopting
standard intrinsic red clump (RC) magnitudes and extinction values, we obtain
first the distance modulus for each cluster and thereafter their heliocentric
distances, that range from about 4 to 20 kpc. Therefore, we are able to place
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. Finally, we find
that all clusters have low-luminosities, with $-6.9<M_{V}<-3.5$ mag.

Conclusions. Based on our photometric analysis, we find both open clusters
(OCs) and globular clusters (GCs) in our sample. In particular, we confirm the
OC nature for Kronberger 100, while we classify Patchick 125 as a metal-poor
GC, Ferrero 54 as a metal-rich GC, and ESO 92-18 as a possible old OC or young
GC. The classification as GC candidates is also suggested for Kronberger 99,
Patchick 122, Patchick 126, Riddle 15, FSR 190 and Gaia 2. We also conclude
that Kronberger 119 and Kronberger 143 might be either old OCs or young GCs.

###### Key Words.:

Galaxy: bulge – Galaxy: center – Galaxy: stellar content – Stars Clusters:
globular – Infrared: stars – Surveys

##  1 Introduction

One of the most important questions in astrophysics that still needs an
explanation is how the Milky Way (MW) bulge was formed and how it has evolved
to the present-state (Di Matteo et al. 2015; Barbuy et al. 2018). Existing
models (e.g., Kormendy & Kennicutt 2004; Gadotti 2009) suggest that bulges can
be classified as classical bulges, if they result from a violent event (i.e.
galaxy mergers or sinking of giant gas clumps); or disk-like bulges, which may
be the consequence of internal processes (e.g., disk instabilities) on longer
time-scales. In the first case, older stellar populations are expected within
a spherical structure; in the second, a wide range of ages for stellar
populations are awaited in a flattened structure.

Very useful tools to reconstruct the MW history as well as to characterise its
current evolutionary stage are the globular clusters (GCs). Being the first
stellar associations (as well as dwarf spheroidal galaxies) formed in the
early Universe with typical lifetimes of $12-14$ Gyr (Salaris & Weiss 2002),
GCs retain fingerprints of past events that have occurred in their host galaxy
(e.g., mergers/interactions). Thus, they provide a channel for tracing the
MW’s properties, such as its structure, dynamics, compositions as well as the
dark matter morphology. However, the number of known MW GCs seems to be small
in comparison with the Andromeda galaxy (Harris et al. 2013; Minniti et al.
2017a) or the Galactic open clusters (OCs; Bonatto & Bica 2010; Cantat-Gaudin
et al. 2018a, 2020), indicating that our Galaxy has been inefficient at
forming GCs, or strong processes have destroyed these objects, or many GCs
have yet to be discovered. Indeed, during the last two decades, many new GCs
have been detected in the Galactic halo thanks to optical photometric surveys,
like the Sloan Digital Sky Survey (SDSS; York et al. 2000), and also across
the Galactic bulge and disk with surveys, such as the near-infrared (NIR) Two
Micron All Sky Survey (2MASS, Skrutskie et al. 2006) and the VISTA Variables
in the Via Lactea (VVV; Minniti et al. 2010; Saito et al. 2012) and its
extension (VVVX; Minniti 2018) surveys. Already more than 300 star cluster
candidates have been discovered within the VVV/VVVX images, but a dedicated
analysis needs to be done in order to confirm their physical nature (e.g.,
Minniti et al. 2017a, b). In fact, the discovery of new GCs towards the
galactic inner regions can be useful to constrain formation and evolution
models of the MW, especially when accurate physical parameters are estimated.
Significant effort has been devoted in the last years to studying the real
nature of GC candidates and indeed many of them have been confirmed. A few
examples are VVV-CL001 (Minniti et al. 2011; Fernández-Trincado et al. 2021b),
VVV-CL002 and VVV-CL003 (Moni Bidin et al. 2011), FSR 1716 (a.k.a. Minni 22;
Minniti et al. 2017b), RLGC 1 and 2 (Ryu & Lee 2018), Camargo 1107, 1108, and
1109 (Camargo & Minniti 2019), FSR 1758 (Barbá et al. 2019; Romero-Colmenares
et al. 2021), Garro 01 (Garro et al. 2020), UKS 1 (Fernández-Trincado et al.
2020), Patchick 99 (Garro et al. 2021b), FSR 19 and FSR 25 (Obasi et al.
2021), VVV-CL160 (Minniti et al. 2021a), Minni 48 (Minniti et al. 2021b), FSR
1776 (a.k.a. Minni 23; Dias et al. 2021), Ton 1 (Fernández-Trincado et al.
2021, in press), and other 9 GCs in Garro et al. (2021c).

The present study provides the photometric analysis of 12 GC low-latitude
candidates, shown in Fig. 1, including measurements of physical parameters, in
order to reveal their real nature.
In Section 2, we introduce these new GC candidates, listed in Table 1. In
Section 3 we briefly quote the datasets adopted. In Section 4, we describe the
methods used to investigate them and how we derive their main physical
parameters. We also add individual notes about each of these clusters in
Section 5. Finally, a summary and discussion are presented in Section 6.

##  2 Cluster candidates

The sample targets, listed in Table 1 and displayed in Figure 1, include 12 GC
candidates. These were selected mostly from the clusters discovered by members
of the Deep Sky Hunters collaboration, a world-wide group of amateur
astronomers dedicated to finding new deep sky objects such as open clusters
and planetary nebulae (Kronberger et al. 2006, 2016). The new clusters were
originally discovered through a visual inspection of the DECam Plane Survey
(DECaPS; Schlafly et al. 2018) as concentrated local enhancements of the
stellar density, as shown by Fig. 12. Besides the recent DECaPS finds, we are
also including some other older discoveries that have yet to be properly
analysed: ESO 92-18 was discovered in the early 80’s as part of the
ESO/Uppsala Survey catalogues (Lauberts 1982), but it also was detected by
Froebrich et al. (2008) and was also listed as MWSC 3250 by Kharchenko et al.
(2013); Gaia 2 was an independent Digitized Sky Survey (DSS) discovery by
Kronberger et al. (2012), but also detected by Koposov et al. (2017) from Gaia
Data Release 2 (Gaia Collaboration et al. 2018b) observations; Riddle 15 was
discovered by Kronberger et al. (2006) and also listed as MWSC 3063 by
Kharchenko et al. (2013).
These clusters are analysed here for the first time, and we have kept their
original names after their discoverers (Kronberger, Patchick, Riddle, and
Ferrero).

Figure 1: Galactic distribution of GCs toward the MW bulge. Star clusters
investigated in this work are highlighted with red points, while open green
squares represent the Galactic GCs by Vasiliev & Baumgardt (2021) in the Gaia
EDR3 footprint.

##  3 The optical and NIR datasets

Investigating these 12 clusters appears a tricky task to perform as many of
these objects are located in obscured regions, behind dust clouds, or they can
be so faint or diffuse that it is difficult to distinguish them against the
background. Also, the presence of patchy differential reddening in front of
some of these clusters represents an additional obstacle to their detailed
analysis. Hence, it is necessary to employ distinct datasets at different
wavelengths, in order to overcome these complications and obtain trustworthy
results. We especially rely on NIR datasets, as in these bands the effect of
extinction due to the dust is greatly reduced with respect to the optical.
Also, since giant stars appear very luminous at these wavelengths, this can
help to derive reliable physical parameters, such as distance and metallicity.
A brief description of the available datasets is presented below.

###  3.1 VVV/VVVX photometry

We use the NIR datasets of the VVV and VVVX surveys. The data were obtained
using the 4.1m wide-field Visible and Infrared Survey Telescope for Astronomy
(VISTA; Emerson & Sutherland 2010) at ESO Paranal Observatory. The VISTA
Telescope tile field of view is 1.501 deg2, and 196 tiles are used to map the
bulge area ($-10^{\circ}<l<+10^{\circ}$, $-10^{\circ}<b<+5^{\circ}$) and 152
tiles for the disk ($-65^{\circ}<l<-10^{\circ}$,
$-2.25^{\circ}<b<+2.25^{\circ}$). Also, the extended VVVX campaign is sampling
a larger area of the sky with the goal of extending the footprint of the VVV
survey by surrounding this previous area in the bulge and the mid-plane areas
at longitudes from 295∘ to 10∘. Both the VVV and VVVX photometric datasets are
divided into several bulge+disk tiles: $d001$ to $d152$ in the disk and $b201$
to $b396$ in the bulge for the VVV, whereas $b401$ to $b512$ in the bulge and
$e601$ to $e988$ in the disk regions for the VVVX regions. The VVVX area also
includes an extension from 230∘ to 295∘ longitude and -2∘ to +2∘ latitude,
those are sampled in the tiles $e1001$ to $e1180$.
The VVV data was reduced at the Cambridge Astronomical Survey Unit (Irwin et
al. 2004) and further processing and archiving was performed with the VISTA
Data Flow System (Cross et al. 2012). For the VVV clusters, we extract the
photometry from the VVV catalog published by Alonso-García et al. (2018). This
catalog was obtained using point-spread function techniques, and is calibrated
into the VISTA photometric system (González-Fernández et al. 2018). A
preliminary catalog from the VVVX data, obtained following a similar approach
(Alonso-García et al., in prep), was used to extract the photometry for the
clusters in the VVVX footprint.

The advantage of using this public survey is that its passbands ($ZYJHK_{s}$
in VVV and $JHK_{s}$ in VVVX) allows us to study in detail evolved stars in
the colour-magnitude diagram (CMD), in particular red clump (RC) stars, which
are good metallicity and distance indicators. Unfortunately, not all star
clusters considered here fall under the VVVX coverage. We detected in the
VVV/VVVX images the following star clusters:

  * •

Ferrero 54 in the VVVX tiles e706,705;

  * •

Kronberger 100 in the VVVX tile e1032;

  * •

Kronberger 143 in the VVV tile d003;

  * •

Patchick 125 in the VVVX tile e932;

  * •

Patchick 126 in the VVVX tile e676.

###  3.2 2MASS photometry: brighter stars

The 2MASS is an all sky survey in $J$, $H$ and $K_{s}$ NIR bands. We recovered
that photometry basically for two reasons. For all clusters that have a
VVV/VVVX counterpart, the 2MASS photometry allows to build a CMD with stars
from the MS to the RGB-tip, while VVV/VVVX stars with $K_{s}<11$ mag are
saturated. To do this, since the 2MASS and VISTA photometric systems are tied
but are different, we transformed the 2MASS photometry into the VISTA
magnitude scale following González-Fernández et al. (2018). On the other hand,
for the other clusters, such as Kronberger 99, Kronberger 119, Patchick 122,
Riddle 15, FSR 190, ESO 92-18 and Gaia 2, which are outside the VVVX coverage,
we obtain the NIR information for the brighter stars. Although in a few cases
the 2MASS star sample appears to be small, we are still able to establish some
of the physical parameters of our targets, such as their metallicity.

###  3.3 Gaia EDR3 photometry

The Gaia Early Data Release 3 (EDR3, Gaia Collaboration et al. 2021)
photometry is handled to build vector proper motion (VPM) diagrams, used to
separate star cluster members from background/foreground stars and confirm the
cluster nature of our sample. Also, its precise astrometry is used to
eliminate all nearby stars with distances $D<2$ kpc (Section 4.1) from our
source catalogues. Additionally, this photometry gives the possibility to
construct deeper CMDs for those clusters without VVV/VVVX data, as we can
appreciate for ESO 92-18 and Gaia 2 CMDs (Fig. 14). No photometric colour or
magnitude cuts were applied to the Gaia EDR3 data.

##  4 Methods

###  4.1 Decontamination procedure

This analysis employs the combination of the VVV/VVVX and 2MASS photometry in
$J$, $H$ and $K_{s}$ bands, and the optical Gaia EDR3 dataset in order to
investigate the nature of these candidates.
First, we join the VVV+Gaia EDR3 and/or the 2MASS+Gaia EDR3 datasets using a
$0.5^{\prime\prime}$ matching radius. We treat separately the two NIR
datasets, making a simple magnitude cut at $K_{s}=11$ mag. After that, we
apply a decontamination procedure in order to build a clean catalogue with
likely-star members of every GC candidate, adopting the same procedure applied
by Garro et al. (2020, 2021b). As a preliminary step, we exclude all nearby
stars with parallax values larger than $0.5$ mas. Subsequently, we select
stars within a given radius $r$, listed in Table 1, from the cluster centre.
We follow two methods in order to derive the cluster size: first, we inspect
the density diagrams as a function of the sky position, as shown in Fig. 2, in
order to visually individuate as an overdensity the cluster dimensions;
second, we apply the Gaussian Kernel Density Estimate (KDE; e.g., Rosenblatt
1956; Parzen 1962). Briefly, considering the scatterplot on the left hand side
of Fig. 3, overlapping points make the figure hard to read. Even worse, it is
impossible to determine how many data points are in each position. In this
case, a possible solution is to cut the plotting window into several bins
(100-300 bins), and represent the number of data points in each bin by a
colour. Following the shape of the bin, this makes 2D histogram. Then, it is
possible to make a smoother result using Gaussian KDE. Its representation is
called a 2D density plot, and we add a isodensity contours to denote each
step. Therefore, we balance both the KDE contours and the visual overdensities
in order to select the stars within a given radius (Table 1). We adopt a GCs
radius of $\sim 3^{\prime}$ for Kronberger 99, Kronberger 143, Ferrero 54 and
ESO 92-18, Gaia 2; while a larger size ($r\approx 10.2^{\prime}$) for FSR 190,
and smaller dimensions ($r<2.5^{\prime}$) for Kronberger 100, Kronberger 119,
Patchick 122, Patchick 125, Patchick 126, Riddle 15. At this level, we benefit
from exquisite Gaia PMs measurements, constructing the vector PMs diagrams
(Fig. 13), in order to keep only stars with high probability of cluster
membership. We are able to estimate the mean cluster PMs, listed in Table 1,
using the $\sigma$-clipping technique. In our final datasets, we include only
stars within 1 mas yr-1 from the mean cluster PM values. Even though the
assumption of a fixed PM radius value to select the final star sample is
rigorous, it is linked to the fact that the PM overdensities, shown in the VPM
diagrams (Fig. 13), which indicate the presence of a cluster, are very small
and peaked in most cases. Also, this allowed us to keep only stars that are
likely members of the clusters (with ¿50% probability), minimizing the
likelihood of including outliers as well as of excluding member stars. For
that reason, we also calculate the PM probability for each star within the
cluster size, as shown in Fig. 13. However, a very small fraction of
contaminants in the final catalogues may be expected since these regions are
characterised by high stellar crowding and by disk stars with similar PMs, as
demonstrated by Garro et al. (2021b). Even if this occurs, it does not have
any significant effect on our final photometric analysis, as the over-density
peaks are clear in the VPM diagrams (Fig. 13) against the background noise,
ensuring that the final catalogues include likely cluster members.
The resulting values are listed in Table 1, where we summarise: the cluster
identification (ID), the position, the radius cuts, the number of star members
($N_{\star}$) and the mean cluster PMs both in RA
($\mu_{\alpha_{\ast}}=\mu_{\alpha}\times\cos\delta$) and in Dec
($\mu_{\delta}$).

Figure 2: Gaia EDR3 density maps, cleaned from nearby stars, centred on ESO
92-18 (on the left) and Kronberger 100 (on the right) fields. These two
clusters are used as representative in order to visually show the different
target sizes. The greener areas are overdensities, while the bluer areas are
lower densities.

Figure 3: KDE technique applied to select the likely size of a cluster during
the decontamination procedure. From left to right: a scatterplot, 2D
Histogram, Gaussian KDE and 2D density with contours (or iso-densities) are
shown for ESO 92-18 (top panels) and Kronberger 100 (bottom panels) fields,
used as representative. Green and yellow areas are illustrative of
overdensities, while the blue areas show lower densities. Figure 4: Optical
DECaPS (left) and NIR VVVX (right) images of the sky region centred on Ferrero
54. The field of view is $200^{\prime\prime}\times 200^{\prime\prime}$,
oriented along the Galactic coordinates, with Galactic longitude increasing to
the left, and Galactic latitude increasing to the top of the images. Veils of
gas and dust are evident as green filaments in the optical passband. They are
part of the Vela supernova remnant complex. Table 1: Positions, selection cuts
applied for the decontamination procedure, number of members and mean cluster
PMs.

Cluster ID RA Dec r $N_{\star}$ $\mu_{\alpha_{\ast}}$ $\mu_{\delta}$
[hh:mm:ss] [dd:mm:ss] [arcmin] [mas yr-1] [mas yr-1] Kronberger 99 09:11:17.6
$-$46:23:27 $3.0^{\prime}$ 21 $-3.62\pm 0.18$ $+4.46\pm 0.19$ Kronberger 100
09:35:54.7 $-$54:01:49 $1.7^{\prime}$ 187 $-3.79\pm 0.33$ $+3.02\pm 0.37$
Kronberger 119 10:47:15.7 $-$63:19:42 $2.4^{\prime}$ 182 $-3.94\pm 0.22$
$+1.80\pm 0.24$ Kronberger 143 11:57:42.6 $-$64:10:40 $3.6^{\prime}$ 148
$-7.76\pm 0.21$ $+0.66\pm 0.22$ Patchick 122 09:42:30.7 $-$52:25:41
$1.6^{\prime}$ 28 $-3.72\pm 0.12$ $+3.81\pm 0.12$ Patchick 125 17:05:00.7
$-$35:29:41 $2.0^{\prime}$ 146 $-3.85\pm 0.50$ $+0.64\pm 0.39$ Patchick 126
17:05:38.6 $-$47:20:32 $0.9^{\prime}$ 108 $-4.75\pm 0.46$ $-6.68\pm 0.62$
Riddle 15 19:11:08.9 $+$14:49:59 $<1^{\prime}$ 83 $-1.03\pm 0.32$ $-1.64\pm
0.27$ FSR 190 20:05:29.3 $+$33:34:01 $10.2^{\prime}$ 52 $-2.41\pm 0.23$
$-3.50\pm 0.24$ Ferrero 54 08:33:48.3 $-$44:26:49 $3.0^{\prime}$ 122 $-1.33\pm
0.27$ $+1.31\pm 0.34$ ESO 92-18 10:14:55.2 $-$64:36:40 $3.0^{\prime}$ 557
$-3.54\pm 0.19$ $+2.72\pm 0.18$ Gaia 2 01:52:33.0 $+$53:02:36 $3.0^{\prime}$
83 $-1.31\pm 0.18$ $+1.21\pm 0.19$

###  4.2 Estimation of physical parameters

Once the final catalogues were obtained, we derived the main physical
parameters for each candidate, such as: the reddenings and extinctions, the
distances, the total luminosities, the ages and the metallicities. The
derivation of these parameters is challenging because in those areas crowded
with additional dust and gas (see Fig. 4), the observations and precise
measurements are made more complicated. Moreover, towards the innermost
regions the differential reddening becomes more prominent increasing the
uncertainties in the determination of distances. Then, the extinction and
distances are estimated following the same procedures described in our
previous works e.g., Garro et al. 2021b and Minniti et al. 2021b. We adopt
existing reddening maps, such as those by Gonzalez et al. (2011), Soto et al.
(2019) and Surot et al. (2019) in the NIR and by Schlafly & Finkbeiner (2011)
in the optical passbands. Therefore, we use the following relations to derive
the color excess and the extinction: $A_{V}=3.1\times E(B-V)$,
$A_{Ks}=0.11\times A_{V}$, $A_{G}=0.86\times A_{V}$, $A_{Ks}=0.75\times
E(J-Ks)$, $A_{G}=10.115\times A_{Ks}$, and $A_{G}=2.0\times E(BP-RP)$. We find
extinction spans of $0.09\lesssim A_{Ks}\lesssim 0.86$ mag and $0.89\lesssim
A_{G}\lesssim 4.72$ mag. The extinction values are mandatory to compute
reliable heliocentric distances, using the position of the red clump (RC). The
advantage of using $M_{Ks}^{RC}$ arises from its simple identification and low
sensitivity to extinction by interstellar dust (e.g., Salaris & Girardi 2002).
Therefore, we adopt the intrinsic RC magnitude $M_{Ks}^{RC}=-1.606\pm 0.009$
mag and $M_{G}^{RC}=0.383\pm 0.009$ mag from Ruiz-Dern et al. (2018), the
observed NIR and optical RC magnitude listed in Table 1 (column 2 and 3), and
the extinction values (column 3 and 4), in order to derive the distance moduli
(column 6). These parameters can be translated into heliocentric distances
(column 7 and 8), finding $4.4\lesssim D_{NIR}\lesssim 18.1$ kpc from the NIR
photometry. Also, both NIR and optical distance values agree well within the
errors, since we find $3.7\lesssim D_{GEDR3}\lesssim 19.5$ kpc from the Gaia
photometry. However, clusters with blue horizontal branches usually do not
show a defined RC, especially in poorly-populated CMDs. Therefore, we derive
the color excess for the optical passband comparing the cluster HB and RGB
colours with the absolute colours by Gaia Collaboration et al. (2018a).
The extinction coefficient that we use in our analysis is $R_{V}=3.1$, which
is the standard value for diffuse interstellar medium (e.g., Sneden et al.
1978). Recent works (Nataf et al. 2013; Pallanca et al. 2021, 2021; Souza et
al. 2021) have demonstrated that a low $R_{V}\approx 2.5-2.7$ is more
appropriate to reproduce the bulge populations, especially in the regions
where Patchick 125 and 126 are located. Clearly, a different extinction value
has an effect on the colour excess and distance estimates. We find that the
distances increase of $\sim 0.1$ kpc for Patchick 125 and $\sim 0.16$ kpc for
Patchick 126 when a low $R_{V}$ is adopted. Nonetheless, both distance values,
obtained adopting $R_{V}=3.1$ and 2.5, are in good agreement within the
errors. Additionally, we note that when we use $R_{V}=2.5$, and we keep the
metallicities and ages, as listed in Table 1, the isochrones do not fit
properly the points (especially along the RGB sequences) in the CMD, unless a
higher metallicity is used, as shown in Fig. 5. However, we argue that
$R_{V}=3.1$ is a good compromise, if we base on the Patchick 125 metallicity
of [Fe/H] $=-1.70$, spectroscopically found by Fernández-Trincado et al.
(2021a) (read Sect. 5.6).

Moreover, we derive their Galactocentric X,Y, Z coordinates in kpc using the
NIR distances. As shown by Fig. 6, we place our candidates at their respective
distances $R_{G}$ from the Galactic centre, assuming $R_{\odot}=8.2$ kpc
(Gravity Collaboration et al. 2019). We find that they are located at
Galactocentric distances ranging between $2.94$ kpc (for Patchick 126) and
$14.06$ kpc (for Riddle 15), as listed in Table 1. Additionally, we calculate
the distance above or below the Galactic plane, using the relation
$Z=D\times\sin(b)$ and assuming $Z_{\odot}=0$ kpc, spanning $-1.23\lesssim
Z\lesssim 0.78$ kpc.

Figure 5: Patchick 125 (bottom panels) and Patchick 126 (top panels) NIR CMDs.
On the left panels, we compare two isochrones using two different extinction
coefficient $R_{V}=3.1$ (yellow points) and $R_{V}=2.5$ (red points). On the
right panels, we fix the $R_{V}=2.5$ and the ages as listed in Table 1, and we
change the metallicity as specified in the legend. Figure 6: Galactocentric
distribution of star clusters analysed in the present work (red points) and
Galactic GCs (green open squares) by Baumgardt & Vasiliev (2021). The black
cross represents the position of the Galactic centre, while the blue star is
the position of the Sun.

Once distances and mean PMs are obtained, we can compute their tangential
velocities ($V_{T}^{RA}$ and $V_{T}^{Dec}$ ). Moreover, we compare the PMs and
$V_{T}$ distributions with those of known and well-characterised MW GCs by
Vasiliev & Baumgardt (2021) as shown in Fig. 7. We obtain negative
$\mu_{\delta}$ for Riddle 15, FSR 190 and Patchick 126, which show
$-8.0<\mu_{\delta}<0$ mas yr-1 and $-10.0<\mu_{\alpha_{\ast}}<0$ mas yr-1;
while all the others display $\mu_{\delta}>0$ mas yr-1 and the same
$\mu_{\alpha_{\ast}}$ range. Also, regarding $V_{T}$, we clearly obtain a
trend similar to that of the PMs, since we find negative $V_{T}^{Dec}$ for
Riddle 15, FSR 190 and Patchick 126, which are $-300<V_{T}^{Dec}<-100$ km s-1,
while for the other clusters $V_{T}^{Dec}$ is always positive between 0 and
200 km s-1, while the $-300<V_{T}^{RA}<0$ km s-1 for all clusters. Obviously
the clusters exhibit the longitude dependence due to the Solar motion around
the Galactic center, but as a whole the new GCs identified here are consistent
with the bulk motions observed for the rest of the MW globular cluster system.

Figure 7: Gaia EDR3 PM-distribution of star clusters in the present work (red
points) and Galactic GCs (open green squares) by Vasiliev & Baumgardt (2021).

Reddenings and distances are crucial to derive the cluster metallicities and
ages. One of the methods that allows to determine these parameters with
reasonable reliability is the isochrone-fitting method. Our CMDs in Fig. 14
are populated by evolved stars, such as RC, blue horizontal branch (BHB) and
red giant branch (RGB). These stars are excellent indicators of the global
metallicity content of a stellar population, as they are more sensitive to the
metallicity variations (McQuinn et al. 2019). However, for Kronberger 100, ESO
92-18 and Gaia 2, fainter main sequence stars are detected by Gaia EDR3
photometry. We use the PARSEC models (Bressan et al. 2012; Marigo et al. 2017)
in order to obtain the metallicity for each cluster, finding a range of
$-1.8\lesssim$ [Fe/H] $\lesssim+0.3$ with a mean error of $\pm 0.2$ dex. On
the other hand, it is well-known that the main sequence turn-off (MSTO) is the
best point to derive the absolute age of a cluster. Yet, some of our Gaia and
VVVX/2MASS CMDs are not deep enough to reach (or go down $\sim 2$ mag below)
the MSTO point, as we can see in Fig. 14, for example, for Riddle 15, Patchick
126 and Kronberger 119. Therefore, our determination of the ages of these
clusters is approximate, and deeper observations are necessary to confirm our
results. However, we find a range of $2<$ Age $<14$ Gyr, well in agreement
with old and intermediate-age Galactic GCs. More precise ages are evaluated
for Kronberger 100, Kronberger 119, Kronberger 143, Patchick 125, ESO 92-18
and Gaia 2, as we detail in Section 5. Additionally, we determine the errors
in age and in metallicity by testing isochrones at a fixed metallicity and a
fixed age, respectively, until they no longer fit the cluster sequence
simultaneously in the NIR and optical CMDs (see Fig. 14).
On the other hand, we apply the $\chi^{2}$ analysis in order to derive the age
and the metallicity as an independent method. We perform this analysis for all
clusters on the Gaia CMDs, since in many cases optical CMDs are deeper than
NIR CMDs, using a family of PARSEC isochrones. We adopt ages between 1 and 13
Gyr, and we change the metallicity values, depending on the [Fe/H] estimates,
listed in Table 1. Figure 8 shows the $\chi^{2}$ values as a function of the
ages, whereas we list the likely age and metallicity corresponding to the
minimum $\chi^{2}_{min}$ value in Table 2. We obtain a good agreement between
the metallicity estimates obtained with the isochrone-fitting and $\chi^{2}$
methods, except for Kronberger 99, for which the $\chi^{2}$ method yields a
lower metallicity ([Fe/H] $=-1.4$). Nonetheless, the age values represent a
lower-limit again, especially for those clusters with few points, as i.e.
Patchick 122. This was expected, since neither the MS nor the MS-TO are
reached in some CMDs. Indeed, for the ESO 92-18 (see Fig. 8, right panel) and
Gaia 2 cases, we obtain an excellent agreement (within $1\sigma$) between the
two methods, due to the fact that the MS-TO and the higher part of the MS are
above the detection limit. Conversely, the FSR 190 CMD is very noisy,
therefore our procedure does not show a clear minimum for the age. For that
reason, we suggest that the estimates for that cluster found by the previous
method and by the comparison with the literature (see Sect. 5.9) are more
reliable.

Figure 8: $\chi^{2}$ estimate as a function of the age for three
representative clusters: ESO 92-18, Patchick 125, Patchick 126. The colour of
the lines depends on the metallicity, specified in the legend. The black
dashed lines indicate the minimum $\chi^{2}$ value at the relative age. The
age and metallicity that correspond to the $\chi^{2}_{min}$ are listed in
Table 2. On the right panel, we show the Gaia EDR3 CMD for ESO 92-18. We fit
the PARSEC isochrone (black dotted line) using the age and metallicity
obtained by the $\chi^{2}$ analysis and listed in Table 2. We clearly used the
reddening, distance modulus and extinction as listed in Table 1.

Furthermore, it is important to note that the PARSEC isochrones are available
for $[\alpha/Fe]=0$, a typical value associated to OCs and metal-rich GCs. In
the case of the metal-poor clusters, such as Kronberger 99, Kronberger 143 and
ESO 92-18, an enhanced $[\alpha/Fe]$ value should be adopted. Therefore, for
these clusters we also used the Dartmouth Stellar Evolution Database (Dotter
et al. 2008), adopting enhanced $[\alpha/Fe]$ values, and keeping age and
metallicity fixed, as listed in Table 1. In Fig. 9, we compare the Dartmouth
and PARSEC isochrones, finding a good agreement between these models. However,
we suggest that these clusters should have $[\alpha/Fe]=+0.2$.
We categorise all clusters with Age $\gtrsim 8$ Gyr and metallicity [Fe/H]
$\lesssim-0.1$ dex as GCs, and the rest as OCs.

Figure 9: Gaia EDR3 optical CMDs for the clusters: Kronberger 99 (left panel),
Kronberger 143 (middle panel), and ESO 92-18 (right panel). Green, yellow and
pink lines are the Dartmouth isochrones with $[\alpha/Fe]=+0.4$, $+0.2$, $0$
respectively. The dotted red lines are the PARSEC isochrones. We keep the age
and metallicity fixed as listed in Table 1.

Finally, the total luminosity in $K_{s}-$band for each cluster is derived
following the same approach of Garro et al. (2021a). We first derive the
absolute magnitude ($M_{Ks}$) measuring the cluster total flux. Although
Kharchenko et al. (2016) have demonstrated that the larger contribution in
luminosity arises from the brightest stars, since the first 10-12 members
accumulate more than half of the integrated luminosity of the cluster, we are
aware that the resulting $M_{Ks}$ are a lower limit, because our photometry
does not include fainter and lower mass stars. Therefore, in order to quantify
the fraction of luminosity missed we adopt the same procedure of Garro et al.
(2021a), comparing the luminosity of our sample with those of known Galactic
GCs. Once this luminosity fraction is obtained, we add this to the absolute
magnitude and convert it into the absolute magnitude in $V-$band. In this way,
we obtain an empirical correction to our clusters’ luminosities under the
assumption of similarity among Galactic GCs. We find that all clusters have
low-luminosities with $-3.5<M_{V}<-6.9$ mag, much fainter than the peak of the
MW GC luminosity function (GCLF) is $M_{V}^{MW}=-7.4\pm 0.2$ mag from Harris
(1991); Ashman & Zepf (1998), also in agreement with the value found by Garro
et al. (2021a) $M_{V}^{MW}=-7.46\pm 1.04$ mag.

Table 2: Main physical parameters for each star cluster candidate, using the
VVV/VVVX, 2MASS and Gaia EDR3 photometry.

Cluster ID $K/K_{s}$aa$a$We refer to $K$ or $K_{s}$ magnitudes for all
clusters analysed adopting the 2MASS or VVV/VVVX datasets, respectively. Also,
both $K/K_{s}$ and $G$ magnitudes listed in the table are the average
magnitudes of the RC.  $G$aa$a$We refer to $K$ or $K_{s}$ magnitudes for all
clusters analysed adopting the 2MASS or VVV/VVVX datasets, respectively. Also,
both $K/K_{s}$ and $G$ magnitudes listed in the table are the average
magnitudes of the RC.  $A_{Ks}$ $A_{G}$ $(m-M)_{NIR}$ $D_{NIR}$bb$b$We adopt
subscripts NIR and GEDR3 in order to indicate if the distance is derived from
the 2MASS and/or VVV/VVVX in NIR or Gaia EDR3 (GEDR3) photometries.
$D_{GEDR3}$bb$b$We adopt subscripts NIR and GEDR3 in order to indicate if the
distance is derived from the 2MASS and/or VVV/VVVX in NIR or Gaia EDR3 (GEDR3)
photometries. $R_{G}$ Z $M_{Ks}$ $M_{V}$cc$c$The absolute magnitude in
$V-$band is calculated from the comparison with the well-known Galactic GCs
following Garro et al. (2021a). Agedd$d$We highlight the age used in the fit
of the isochrones (Fig. 14) in square brackets. [Fe/H] Typeee$e$The
abbreviations indicate: GC?=globular cluster candidate; OOC=old open cluster
or young globular cluster; GC=globular cluster; OC=open cluster. [mag] [mag]
[mag] [mag] [mag] [kpc] [kpc] [kpc] [kpc] [mag] [mag] [Gyr] [dex] Kronberger
99 $12.60\pm 0.03$ $17.9\pm 0.002$ $0.62\pm 0.01$ $4.48\pm 0.09$ $13.23\pm
0.03$ $4.42\pm 0.4$ $3.70\pm 0.4$ $9.42\pm 0.4$ 0.09 $-6.02\pm 1.9$ $-3.6$
$>6-8\ [8]$ $-0.8\pm 0.2$ GC? Kronberger 100 $12.92\pm 0.03$ $17.37\pm 0.001$
$0.37\pm 0.01$ $2.76\pm 0.10$ $14.14\pm 0.03$ $6.76\pm 0.4$ $6.65\pm 0.5$
$10.0\pm 0.5$ $-0.17$ $-4.88\pm 1.8$ – $2-5\ [3]$ $+0.3\pm 0.3$ OC Kronberger
119 $13.90\pm 0.06$ $17.4\pm 0.003$ $0.24\pm 0.01$ $1.85\pm 0.03$ $15.27\pm
0.06$ $11.30\pm 0.5$ $9.8\pm 0.5$ $11.54\pm 0.5$ $-0.74$ $-6.27\pm 1.2$ $-4.3$
$6\pm 1$ $-0.5\pm 0.2$ OOC Kronberger 143 $12.90\pm 0.01$ $17.7\pm 0.001$
$0.45\pm 0.01$ $3.12\pm 0.10$ $14.06\pm 0.02$ $6.50\pm 0.4$ $6.30\pm 0.4$
$7.81\pm 0.4$ $-0.22$ $-6.86\pm 1.6$ $-4.9$ $>5-8\ [5]$ $-0.6\pm 0.2$ OOC
Patchick 122 $12.75\pm 0.05$ $18.2\pm 0.002$ $0.63\pm 0.01$ $4.40\pm 0.10$
$13.72\pm 0.05$ $5.60\pm 0.4$ $4.60\pm 0.4$ $9.41\pm 0.4$ $0.04$ $-6.12\pm
1.0$ $-4.2$ $>6\ [8]$ $-0.5\pm 0.2$ GC? Patchick 125 $--$ $--$ $0.33\pm 0.01$
$2.56\pm 0.05$ $15.18\pm 0.05$ $10.90\pm 0.5$ $11.2\pm 0.5$ $3.23\pm 0.5$
$0.65$ $-6.1\pm 0.8$ $-3.8$ $14\pm 2$ $-1.8\pm 0.2$ GC Patchick 126 $13.50\pm
0.01$ $18.0\pm 0.002$ $0.44\pm 0.01$ $2.66\pm 0.07$ $14.66\pm 0.02$ $8.60\pm
0.4$ $7.40\pm 0.5$ $2.94\pm 0.4$ $-0.57$ $-5.56\pm 0.8$ $-3.5$ $>8$ $-0.7\pm
0.3$ GC Riddle 15 $--$ $--$ $0.52\pm 0.01$ $3.09\pm 0.06$ $16.29\pm 0.02$
$18.10\pm 0.5$ $19.5\pm 0.5$ $14.06\pm 0.5$ $0.78$ $-7.6\pm 0.8$ $-6.2$ $>10\
[13]$ $-1.4\pm 0.2$ GC FSR 190ff$f$We mark FSR 190, due to the high extinction
which does not allow us to accurately calculate all the physical parameters
especially in the optical passband.  $14.4$ $20.1?$ $0.86$ $4.72?$ $15.14$
$10.67$ $9.5?$ 11.11 $0.18$ $-8.36$ $-6.9?$ $>7\ [9]$ $-0.9\pm 0.2$ GC?
Ferrero 54 $13.25\pm 0.03$ $17.8\pm 0.002$ $0.60\pm 0.01$ $3.00\pm 0.09$
$14.27\pm 0.03$ $7.10\pm 0.4$ $7.26\pm 0.5$ $11.5\pm 0.4$ $-0.32$ $-5.87\pm
1.7$ $-4.1$ $>10\ [11]$ $-0.2\pm 0.2$ GC ESO 92-18 $13.51\pm 0.05$ $16.3\pm
0.001$ $0.09\pm 0.002$ $0.89\pm 0.01$ $15.12\pm 0.05$ $10.60\pm 0.5$ $9.60\pm
0.5$ $11.35\pm 0.5$ $-1.23$ $-7.3\pm 1.5$ $-5.6$ $5\pm 1$ $-0.9\pm 0.2$ OOC
Gaia 2 $--$ $--$ $0.10\pm 0.002$ $0.97\pm 0.02$ $13.43\pm 0.01$ $4.91\pm 0.5$
$4.43\pm 0.6$ $12.03\pm 0.5$ $-0.75$ $-5.4\pm 2.0$ $-3.9$ $10\pm 1$ $-0.9\pm
0.2$ GC

111

Table 3: $\chi_{2}$ analysis performed for the clusters sample in order to
statistically estimate age and metallicity values.

Cluster ID [Fe/H] (dex) Age (Gyr) Kronberger 99 $-1.4$ 6.0 Kronberger 100
$+0.3$ 3.6 Kronberger 119 $-0.9$ 4.4 Kronberger 143 $-0.9$ 4.4 Patchick 122
$-0.5$ 4.3 Patchick 125 $-1.7$aa$a$We adopt the metallicity found by
Fernández-Trincado et al. (2021a). 8.2 Patchick 126 $-0.5\ /-0.6$ 5.6 Riddle
15 $-0.9\ /-1.4$ 10.4 FSR 190 $-0.9$ – Ferrero 54 $-0.3$ 6.5 ESO 92-18 $-0.8$
4.3 Gaia 2 $-0.9$ 9.8 222

##  5 Fundamental parameters for each cluster

###  5.1 Kronberger 99

We analyse Kronberger 99 by matching Gaia EDR3 and 2MASS datasets, because
this cluster is outside of the VVVX field. Kron-berger 99 appears as an
overdensity both in the Gaia EDR3 and 2MASS images, especially when foreground
stars are excluded. Inspecting the VPM diagram, we can easily extract the mean
cluster PM, as shown in Fig. 14, however after the PM-decontamination
procedure, we find a very poorly-populated cluster with 21 giant members. We
select it as a GC candidate, since a scarcely-populated RC can be observed at
$K=12.6$ mag and $G=17.9$ mag. The analysis yields an extinction and distance
modulus for the cluster of $A_{Ks}=0.62$ mag and
$(m-M)_{0}\leavevmode\nobreak\ =\leavevmode\nobreak\ 13.23$ mag, equivalent to
$D_{NIR}=4.42$ kpc, in good agreement with $D_{GDR3}=3.7$ kpc, within
1$\sigma$. This also places this cluster at $R_{G}=9.42$ kpc from the Galactic
centre. The best PARSEC isochrone fit implies a metallicity of [Fe/H]
$=-0.8\pm 0.2$. On the other hand, due to the sparse population and lack of
faint stars, it is very difficult to establish the age of this cluster.
However, at [Fe/H]$=-0.8$, we superimpose several isochrones with different
age values, finding that all models with Age $<6$ Gyr deviate considerably
from the position of the giant stars in the CMD, in particular the RGB
sequence, which is not the case for older ages. Also, computing the difference
in magnitude between the HB and MSTO (e.g., Salaris & Cassisi 2005; Cassisi &
Salaris 2013) we find that $\Delta K$ (HB-MSTO) is greater than 1.5 mag, which
can be translated into a lower age limit of $\sim 6$ Gyr, which is also in
agreement with that found by the $\chi^{2}$ analysis.

###  5.2 Kronberger 100

Kronberger 100 is investigated using the matches between Gaia EDR3+2MASS and
Gaia EDR3+VVVX datasets. Approximately twenty bright stars are evolved off the
MS, whereas the bulk of the probable cluster members form a populated MS, as
we can appreciate from the CMDs (Fig. 14). We estimate an extinction of
$A_{Ks}=0.37$ mag in the NIR and $A_{G}=2.76$ mag in the optical. This places
Kronberger 100 at a distance modulus of $(m-M)_{0}=14.14$ mag, equivalent to
$D_{NIR}=6.76$ kpc, which is in very good agreement with the heliocentric
distance obtained from the Gaia EDR3 photometry ($D_{GDR3}=6.65$ kpc.)
Additionally, we obtain a distance from the Galactic centre of $\sim 10.0$
kpc. The MSTO point lies near $K_{s}=15.5\pm 0.1$ mag. The best PARSEC
isochrone fit and also the $\chi^{2}$ analysis yield a mean cluster age of
$\sim 3$ Gyr, however ages between 2 and 5 Gyr may be adequate to reproduce
the sequences of this cluster, while the mean metallicity is [Fe/H] $=+0.3\pm
0.3$ dex. Hence, we classify it as an open cluster (OC), containing 187 stars.

###  5.3 Kronberger 119

Matching Gaia EDR3 and 2MASS catalogues, we analyse Kron-berger 119, finding a
cluster with 182 members. Both in the 2MASS and Gaia CMDs a clear overdensity
depicting the RC is seen at $K=13.9$ mag and $G=17.4$ mag, respectively. This
helps us to derive the extinction of $A_{Ks}=0.24$ mag and $A_{G}=1.85$ mag,
and also the distance modulus of $(m-M)_{0}=15.27$ mag, corresponding to
$D_{NIR}=11.30$ kpc. However, we found a smaller distance of $D_{GEDR3}=9.8$
kpc from the Gaia photometry. Adopting the NIR distance, we place this cluster
at $\sim 11.54$ kpc from the Galactic centre. As we can appreciate from Fig.
14, the MSTO is not reached in the 2MASS CMD, however we have a deeper optical
CMD, which allows us to derive a good age estimate, since we evaluated as MSTO
point the overdensity at $G=19.9\pm 0.1$ mag, evident also when cluster
luminosity function is used. Therefore, fitting the PARSEC isochores, we
categorise Kronberger 119 as a young GC or an old OC with an Age $=6\pm 1$ Gyr
and mean metallicity of [Fe/H] $=-0.5\pm 0.2$ dex. However, we found slightly
younger age of 4.4 Gyr and lower metallicity of $-0.9$ with the $\chi^{2}$
analysis.

###  5.4 Kronberger 143

Kronberger 143 falls in the VVVX coverage area, so we examine this cluster
using a match of Gaia EDR3+2MASS and Gaia EDR3+VVVX catalogues. From our
decontamination procedure, we find that this cluster contains 148 members.
Also, a well-defined RGB and RC, and the TO region are demarcated both in the
NIR and optical CMDs (Fig. 14). We estimate its main cluster parameters:
extinction of $A_{Ks}=0.45$ mag and $A_{G}=3.12$ mag, $(m-M)_{0}=14.06$,
equivalent to $D_{NIR}=6.5$ kpc, in excellent agreement with $D_{GEDR3}=6.3$
kpc. This places it at $7.81$ kpc from the Galactic centre. We classify
Kronberger 143 as a young GC with an Age $>5$ Gyr, which represents a solid
lower limit due to the fact that when younger isochrones are fitted, they do
not reproduce any sequences (especially the MSTO region), while models with
ages younger than 8 Gyr are more suitable for this cluster. Similar results
are achieved through the $\chi^{2}$ analysis.

###  5.5 Patchick 122

Patchick 122 is investigated using a combination of Gaia EDR3 and 2MASS
photometry. This is a small ($r\approx 1.6^{\prime}$) and poorly populated
cluster with 28 star members. We select it as GC candidate since a clear
overdensity is obvious in the VPM diagram (Fig. 14), but also a minute RC can
be identified at $K_{s}=12.75$ mag and $G=18.2$ mag. We can speculate about
it, suggesting that this may be a dissolved cluster, a survivor of strong
dynamic processes, or that we suffer of incompleteness. Nonetheless, we derive
its main physical parameters, such as an extinction of $A_{Ks}=0.63$ mag and
$A_{G}=4.4$ mag, and a distance modulus of $(m-M)_{0}=13.72$, corresponding to
$D_{NIR}=5.6$ kpc, in agreement within $2\sigma$ with the optical estimate of
$D_{GDR3}=4.6$ kpc. Using the NIR heliocentric distance, we place this cluster
at $R_{G}=9.41$ kpc from the Galactic centre. Patchick 122 may be a good GC
candidate, since when PARSEC isochrones are fitted we obtained an Age $>6$ Gyr
and metallicity of [Fe/H] $=-0.5\pm 0.2$ dex. Clearly, it is very difficult to
reliably pinpoint the age of this cluster given the scarcity of stars
detected. Hence, in order to overcome the age-metallicity degeneration, we
estimate the age based on the vertical method. We find $\Delta G$ (HB-MSTO)
$\gtrsim 2.0$ mag and $\Delta K$ (HB-MSTO) $\gtrsim 2.5$ mag, which can be
translated into a lower limit of $\sim$ 6 Gyr. On the other hand, the
$\chi^{2}$ analysis suggests a younger age of 4.3 Gyr. For that reason, we fit
models with Age $<6$ Gyr but keeping the metallicity fixed at [Fe/H]$=-0.5$
(obtained also by the $\chi^{2}$ procedure), finding that the isochrones shift
to lower magnitudes and towards the reddest part of the CMD, deviating
significantly from the brightest stars. Therefore, we can exclude that this
cluster is younger than 6 Gyr.

###  5.6 Patchick 125

We analyse Patchick 125 matching Gaia EDR3+2MASS and Gaia EDR3+VVVX datasets.
After the decontamination procedure, we find a small cluster with 146 star
members. We derive its main physical parameters, obtaining an extinction of
$A_{Ks}=0.33$ mag in NIR and $A_{G}=2.56$ mag in optical, a distance modulus
of $(m-M)_{0}=15.18$ mag, equivalent to a heliocentric distance of
$D_{NIR}=10.90$ kpc, in good agreement with the optical passbands
($D_{GEDR3}=11.2$ kpc). The NIR distance places this cluster at $3.23$ kpc
from the Galactic centre. Analysing the PM-decontaminated CMDs, we can clearly
observe an extended BHB, suggesting a metal-poor content. Indeed, the best
PARSEC isochrones fit yields an Age $=14\pm 1$ Gyr and [Fe/H] $=-1.80\pm 0.2$
dex, confirming that Patchick 125 is an old GC. We evaluated its age using two
observables: (i) calculating the difference in magnitude between the HB and
MSTO, finding $\Delta K_{s}$(HB-MSTO) $>4$ mag and $\Delta G$(HB-MSTO) $>3$
mag, translating it into a solid limit of $\sim 13$ Gyr; (ii) we considered
the RGB-tip, which is less sensitive to age changes, but fitting models with
Age $<13$ Gyr the isochrone-tip moves to brighter magnitudes. Therefore, we
suggest that its age may be very old, in contrast with the $\chi^{2}$ method.
Additionally, we find that Patchick 125 is located within $\sim
10.2^{\prime\prime}$ from the centre of the recently discovered GC Gran 3
(Gran et al. 2021). Therefore, we believe that both objects are the same
cluster. However, we keep the original name, referring us to the astronomer
(Dana Patchick in 2018, internal communication) who discovered it first.
Comparing the present work with Gran et al. (2021), we find similar results.
In particular, the mean cluster PMs $\mu_{\alpha_{\ast}}=-3.78$ mas yr-1 and
$\mu_{\delta}=+0.66$ mas yr-1, the Gaia EDR3 extinction $A_{G}=2.60$ mag and
the absolute magnitude in $V-$band $M_{V}=-6.02$ mag are in excellent
agreement with our results. However, they found a more metal-poor cluster with
[Fe/H] $=-2.37\pm 0.18$, relying on the relation between CaT EW and the
magnitude of the HB in the Jonhson V filter. On the other hand, our
metallicity is in good agreement with that derived by Fernández-Trincado et
al. (2021a), since they obtained a mean [Fe/H] $=-1.70$, measuring the Fe I
lines from the APOGEE-2S data.

Moreover, we searched for RR Lyrae stars in the cluster field. Indeed,
according to Clementini et al. (2019), there are 28 RR Lyrae located within
$20’$ from the centre of the cluster Patchick 125. Figure 10 shows their
positions, magnitudes, and period versus amplitude diagrams. Based on their
positions, magnitudes and PMs, we consider that two of them are bona-fide
cluster members: Gaia DR2 5977224553266268928 and DR2 5977223144516980608,
located at $79^{\prime\prime}$ and $81^{\prime\prime}$ from the cluster
centre, respectively. These stars are highlighted with blue points in Figure
10, and their mean magnitudes are $G=18.023\pm 0.016$ and $17.753\pm 0.013$
mag, their mean PMs are $\mu_{\alpha_{\ast}}=-4.067\pm 0.330$,
$\mu_{\delta}=0.362\pm 0.224$ mas yr-1, and $\mu_{\alpha_{\ast}}=-3.793\pm
0.270$, $\mu_{\delta}=0.853\pm 0.185$ mas yr-1, respectively. Their mean
periods are $P=0.601940$ and $P=0.738296$ day, and their amplitudes are
$A=0.872$, and $A=0.633$ mag in the optical passband (Clementini et al. 2019),
respectively. The other RR Lyrae in the field, located beyond $2’$ from the
cluster centre may not be securely considered cluster members because of their
different magnitudes and PMs. In particular, we exclude the other two
variables located within 500 arcsec, because their PMs do not match the mean
cluster PMs. Additionally, we derive their distances using the period-
luminosity-metallicity (PLKZ) relation by Alonso-García et al. (2021).
Firstly, we transformed the Patchick 125 metallicity (listed in Table 1) into
$\log$ Z using the relation shown in Navarrete et al. (2017), assuming
$f=10^{[\alpha/Fe]}=3$ and $Z_{\odot}=0.017$. We find $D=11.06\pm 0.30$ kpc
for Gaia DR2 5977224553266268928, and $D=12.17\pm 0.50$ kpc Gaia DR2
5977223144516980608, both values in excellent agreement with the cluster
distances obtained from the VVVX and Gaia EDR3 photometries. We also changed
the $\alpha$-element enhancement factor $f=1.58$ (adopting the
$[\alpha/Fe]=+0.2$), and we find for Gaia DR2 5977224553266268928 a distance
of $10.4$ kpc and for Gaia DR2 5977223144516980608 a distance of $11.5$ kpc,
in excellent agreement with the NIR cluster distance. However, we test our
estimates using different PLKZ relations by Muraveva et al. (2015), Gaia
Collaboration et al. (2017) and Navarrete et al. (2017), yielding slightly
larger distance values. However, these relations are still within the mean
errors of $0.3$ and $0.5$ kpc obtained by the comparison between these four
PLKZ relations.
The presence of two RRab members of this cluster also support the conclusion
that Patchick 125 is an old and metal-poor GC. In particular, the position of
these two member RR Lyrae in the period-amplitude diagram (shown in the bottom
right panel of Figure 10) suggest that Patchick 125 is an Oosterhoff type II
GC. The mean ridge lines, used in Fig. 10, for the Oosterhoff type I and II
populations are taken from Clement & Shelton (1999), assuming
$A_{V}/A_{I}\approx 1.4$ mag.

Figure 10: Position (top left panel), magnitude-separation (top right panel),
Gaia EDR3 PM-distribution (bottom left panel) and period-amplitude (bottom
right panel) diagrams for the RR Lyrae stars located within $20’$ from the
centre of the cluster Patchick 125. The mean ridge lines for the Oosterhoff
type I and II s populations (left and right dotted lines, respectively) are
taken from Clement & Shelton (1999). We mark as blue points the two RR Lyrae
members.

###  5.7 Patchick 126

We use a combination of Gaia EDR3 and the NIR 2MASS and VVVX datasets in order
to investigate Patchick 126. For this cluster, the CMDs convey a well-defined
RGB and a poorly populated RC at $K=13.5$ mag and $G=18.0$ mag. We estimate an
extinction of $0.441$ mag in the NIR and $2.66$ mag in the optical. From these
parameters, we obtain a distance modulus of $(m-M)_{0}=14.66$ mag, which
places it at a heliocentric distance of $8.6$ kpc, in agreement with
$D_{GEDR3}=7.4$ kpc found from the Gaia photometry, within $2\sigma$. Also, we
derive its distance from the Galactic centre, $R_{G}=2.94$ kpc. Our
photometric analysis suggests that this may be a GC. We found the mean
metallicity of the cluster is [Fe/H] $=-0.7\pm 0.3$ dex and an age older than
8 Gyr, which were evaluated using the isochones fitting method. Although the
metallicities derived from the two methods are in agreement, we find a younger
age of 5.6 Gyr with the $\chi^{2}$ procedure. Therefore, as done for the other
clusters, we calculated the difference in magnitude between the HB and MSTO
also for Patchick 126, obtaining $\Delta K_{s}$(HB-MSTO) $>2.5$ mag and
$\Delta G$(HB-MSTO) $>2.5$ mag, this can be translated into a lower age limit
of 8 Gyr. Additionally, taking its relatively low metallicity into account,
Patchick 126 could be a younger GC, based on the 108 stars selected as
members.

###  5.8 Riddle 15

Riddle 15 is studied using the match between Gaia EDR3 and 2MASS photometry,
because it is outside of the VVVX footprint. It appears confined within a
radius smaller than $1^{\prime}$. That makes this candidate one of the
smallest in our sample, suggesting that it may be located at a large distance.
Indeed, we find $D_{NIR}=18.1$ kpc in NIR and $D_{GDR3}=19.5$ kpc in the
optical, also its Galactocentric distance is $R_{G}=14.06$ kpc. The main
distance error source is related to the dust effect, since we find higher
extinction values of $A_{Ks}=0.52$ mag and $A_{G}=3.09$ in NIR and optical
passbands, respectively. The only information that CMDs display is relative to
its 83 brighter stars. Fortunately, we are able to reach below the HB,
revealing an extended HB. Indeed, we derive its metallicity using the PARSEC
isochrones, yielding [Fe/H] $=-1.4\pm 0.2$ dex. Taking into account both the
low metal content and the magnitude level of the HB at $G\approx 20.0$ mag, we
believe that this cluster may be older than 10 Gyr, with the best isochrone
fit suggesting an age of $\sim 13$ Gyr, in good agreement with the $\chi^{2}$
analysis. However, Bica et al. (2019) classify Riddle 15 as an OC candidate or
a compact OC remnant candidate. The latter based their analysis on 2MASS data
whose depth and angular resolution are clearly not appropriate for getting
reasonable results for this faint, small, and distant cluster.

For that reason, we searched for RR Lyrae stars in the cluster field, since
they are good tracers of old and metal-poor populations. We found one RR Lyra
type-ab variable star located at $43^{\prime\prime}$ from the Riddle 15
cluster centre. This star is Gaia DR2 4320480608680062080, with mean magnitude
$G=20.254\pm 0.012$, period $P=0.608333$ day, Epoch (JD) = 2456956.0055,
Amplitude $A=0.57$ mag in the optical passband, proper motions
$\mu_{\alpha_{\ast}}=-1.90\pm 1.14$ mas yr-1 and $\mu_{\delta}=-1.79\pm 1.05$
mas/ yr-1 (Clementini et al. 2019). Also, we derive its absolute magnitude in
$G-$band adopting the $M_{G}-$[Fe/H] relation by Muraveva et al. (2018),
assuming the [Fe/H] $=-1.4$ as Riddle 15. Hence, this allows us to derive its
distance $D=20.0\pm 0.5$ kpc, in agreement with the cluster distance found
from Gaia EDR3 photometry.
The position, magnitude and PMs for this RR Lyra are consistent with cluster
membership, also suggesting that Riddle 15 is a relatively old and metal-poor
GC, excluding the OC nature.
There is another RR Lyra type-c candidate, Gaia DR2 4320478237881151488,
located at $10’$ from the Riddle 15 centre. However, this is likely a field
star because it is too bright ($G=15.947\pm 0.006$ mag) and its PMs are too
large ($\mu_{\alpha_{\ast}}=3.54\pm 0.07$ mas yr-1 and $\mu_{\delta}=-13.79\pm
0.07$ mas yr-1) to be considered a cluster member.

###  5.9 FSR 190

It is very hard to analyse the field of FSR 190 cluster because of heavy
crowding and differential reddening. In fact, this cluster appears to be
highly reddened as we can appreciate from its CMDs (Fig. 14). We derived an
extinction of $A_{Ks}=0.86$ mag in NIR and $A_{G}=4.72$ mag in optical.
Additionally, the main information from its CMDs, is related to 52 brighter
star members, using a combination of Gaia EDR3 and 2MASS catalogues. From our
analysis, we find that FSR 190 may be a GC, located at a heliocentric distance
of $D_{NIR}=10.67$ kpc and at a Galactocentric distance of $R_{G}=11.11$ kpc.
In the optical passband, we find a slightly smaller distance of
$D_{GEDR3}=9.5$ kpc, but this value is more uncertain because of the high
extinction. The best PARSEC isochrone fit suggests a metallicity of [Fe/H]
$=-0.9\pm 0.2$ dex. With the metallicity fixed, we searched for the best age,
finding Age $>9$ Gyr. However, placing a small RC at $K=14.4$ mag and $G=20.1$
mag, and supposing that all the stars below $K=16.0$ mag are MSTO stars, the
cluster could have an age younger than 7 Gyr, but still in excess of 2 Gyr. if
we use a family of isochrones with Age $<7$ Gyr, these differ considerably
from the observational points of both CMDs. Therefore, we constrained the age
of the cluster to be larger than 7 Gyr.
Although the analysis of this cluster turns out to be tricky and with many
question marks, we are in full agreement with the results of Froebrich et al.
(2008). They derived for FSR 190 similar values, such as metallicity ([Fe/H]
$-0.9\pm 0.4$), age (Age $>7$ Gyr) and extinction ($A_{K}=0.8\pm 0.1$ mag), as
well as similar values of distances ($D=10.0\pm 1.0$ kpc and $R_{G}=10.5\pm
0.8$ kpc, adopting a $R_{\odot}=7.2$ kpc) within the errors. Our results also
agree with the recent results of Cantat-Gaudin et al. (2018b). Also, Bica et
al. (2019) suggested that FSR 190 may be an OC or GC candidate, commenting
that it could be a Palomar-like GC.

###  5.10 Ferrero 54

The main obstacle for the study of Ferrero 54 is the presence of a nebulosity
of dust and gas in front of this cluster, as shown from the optical DECaPS
image (Fig. 4), which disappears in the NIR image. These wisps are part of the
Vela Supernova remnant complex.The decontamination procedure reveals a cluster
including 122 giant stars, with a sparsely populated RC at
$K\leavevmode\nobreak\ =\leavevmode\nobreak\ 13.25$ mag and $G=17.8$ mag. Its
extinction is $A_{Ks}=0.60$ mag and $A_{G}=3.0$ mag. Using these values and
the position of RC stars, we recover the distance modulus of $(m-M)_{0}=14.27$
mag, equivalent to $D_{NIR}=7.1$ kpc, which is in excellent agreement with
that found from the Gaia photometry of $D_{GEDR3}=7.26$ kpc. The NIR distance
places Ferrero 54 at $R_{G}=11.5$ kpc from the Galactic centre. The PARSEC
isochrones fit yields a metallicity of [Fe/H] $=-0.2\pm 0.2$ dex and an Age
$\approx 11$ Gyr. We find that the metallicity estimates derived from the
isochrone-fitting and $\chi^{2}$ methods are in good agreement, on the other
hand the $\chi^{2}$ procedure yields a younger age of 6.5 Gyr. Nevertheless,
we give a solid lower age limit using the vertical method as done for other
clusters, finding $\Delta K_{s}$(HB-MSTO) $>3.0$ mag and $\Delta G$(HB-MSTO)
$>3.0$ mag, which can be translated into a lower limit of $\sim 10$ Gyr.
Additionally, GCs with almost solar metallicities are very scarce, and also in
general they are located in the Galactic bulge. So if the high metallicity of
Ferrero 54 is confirmed, it would make this an exceptional object among the
group of Galactic GCs. Finally, based on our analysis, we confirm the GC
nature for Ferrero 54.

###  5.11 ESO 92-18

As expected from the density diagrams (Figs. 2 and 3), ESO 92-18 is the most
populated cluster here examined, containing 557 star members after the Gaia
EDR3 PM-decontamination procedure. We use the matched Gaia EDR3+2MASS datasets
in order to have the NIR counterpart, even if we lose many fainter stars in
the 2MASS CMD. However, reliable results can be achieved especially when the
Gaia EDR3 CMD is analysed, since main evolutionary sequences are visible: the
brightest MS stars and the MSTO point (at $G=18.8$ mag), a compact RC (at
$K=13.51$ mag and at $G=16.3$ mag) and a well-defined RGB. The main parameters
that we estimated for this cluster are extinctions of $A_{Ks}=0.09$ mag and
$A_{G}=0.89$, a distance modulus of $(m-M)_{0}=15.12$ mag, corresponding to
$D=10.6$ kpc, in good agreement with $D_{GEDR3}=9.6$ kpc from the Gaia
passband, its Galactocentric distance is $R_{G}=11.35$ kpc. Fitting the PARSEC
isochrone models we found that ESO 92-18 may be an old OC or young GC with an
Age $=5\pm 1$ Gyr and a metallicity of [Fe/H] $=-0.9\pm 0.2$ dex, which are in
excellent agreement with the parameters derived from the $\chi^{2}$ analysis.
Our results agree with the parameters obtained by Salaris et al. (2004), and
Shao & Li (2019), especially when ages are compared. Also Bica et al. (2019)
classified ESO 92-18 as an OC.

###  5.12 Gaia 2

Gaia 2 is inspected matching the Gaia EDR3+2MASS datasets. Although the 2MASS
CMD is not so clear to interpret, the Gaia EDR3 CMD shows the MSTO point at
$G=17.7$ mag as a clear overdensity, the highest part of the MS stage, but
also a poorly populated (11 stars) RGB. We can use these sequences in order to
determine its main physical parameters. Indeed, we estimate an extinction of
$A_{Ks}=0.10$ mag and $A_{G}=0.97$ mag, a distance modulus of
$(m-M)_{0}=13.43$ mag, which can be translated into a heliocentric distance of
$D_{NIR}=4.91$ kpc, in very good agreement with $D_{GEDR3}=4.43$ kpc, and a
Galactocentric distance of $R_{G}=12.03$ kpc. The best isochrone fit yields an
Age $=10\pm 1$ Gyr and a metallicity of [Fe/H] $=-0.9\pm 0.2$ dex, which are
in good agreement with the values obtained from the $\chi^{2}$ analysis. This
time the uncertainties about the metallicity are higher than age due to the
lack of evolved stars (especially of the RC or BHB), but also because the MSTO
point is less sensitive to metallicity changes. Additionally, since this
cluster is near to the Sun, we calculate its distance using the Gaia EDR3
parallax values. We use the bayesian distances provided by Bailer-Jones et al.
(2021), finding a mean value of $D=3.57\pm 1.08$ kpc, in good agreement with
the previous estimate, within $1\sigma$.
Moreover, we compare our results with Bica et al. (2019), which catalogued
this cluster as a ultra-faint ($M_{V}=-2$ mag) GC, located at heliocentric
distance $5.4$ kpc, in agreement within $1\sigma$ with our estimates. Finally,
we classify Gaia 2 as a good GC candidate.

##  6 Summary and discussion

We present the first physical characterization of twelve newly discovered
stellar clusters. A dedicated decontamination procedure is carried out in
order to select the PM-star members. There are several difficulties usually
found in this kind of study: from the differential reddening that distorts the
evolutionary sequences in the CMDs (as shown e.g. by the FSR 190 CMDs in Fig.
14) and introduce uncertainties in the observed parameters (e.g., distance
estimates), to the high stellar crowding, which may contaminate the final
catalogue or alter the total luminosity of the cluster, or to the presence of
nebulosity as in the case of Ferrero 54 (Fig.4). For these reasons, our
photometric analysis is based on the combination of the optical Gaia EDR3 and
NIR VVVX/2MASS datasets in order to obtain reliable parameters and understand
the real nature of these low-luminosity objects.

Existing reddening maps in the NIR and in the optical are adopted in order to
derive the extinction values. We find a wide range of $0.09\lesssim
A_{Ks}\lesssim 0.86$ mag in NIR and between $0.89\lesssim A_{G}\lesssim 4.72$
mag in the optical. Using these parameters and intrinsic RC colour and
magnitude values, we are able to measure the distance modulus for each
cluster, translating them into heliocentric distances. We find a large
distance range between 4.4 and 18.1 kpc that place them at 2.94 and 14.06 kpc
from the Galactic centre.
Ages and metallicities are evaluated adopting the isochrone-fitting method,
using the PARSEC model. We find that 8 clusters show rich/intermediate metal
content with [Fe/H] between $-0.5$ and $-0.9$, one young cluster with [Fe/H]
$=+0.3$, and there are two are metal-poor clusters with [Fe/H] $=-1.4$ and
$-1.8$. Regarding the age, for most of our clusters we are only able to
provide a lower limit, using the vertical method since the MSTO point is below
the detection limit.

Figure 11: Age as function of NIR heliocentric distance (top panel) and of
Galactocentric distance $R_{G}$ (bottom panel) for our sample. We also show
the age error bars, even if not all clusters have errorbars in their ages in
Table 1. However, we consider as lower-error the lower limit written in Table
1, whereas as higher-error we adopt the higher limit of 13 Gyr, the typical
age of old Galactic GCs, therefore we constrain the age error as the
difference between our age estimates and 13 Gyr.

However, we can better constrain the ages of the following clusters:
Kronberger 100, Kronberger 119, Kronberger 143, Patchick 125, ESO 92-18 and
Gaia 2. As shown in Fig. 11, we find clusters with a wide range of ages. The
majority of clusters populate the Galactic thin and thick disk and exhibit
ages from 2 Gyr to 13 Gyr. However, we also identify two old clusters
(Patchick 125 and Patchick 126) that are located well inside the Galactic
bulge. Their ages of 14 Gyr and $>8$ Gyr, respectively, are inline with the
results from previous works implying that the lower age limit for the MW bulge
is $\sim 5$ Gyr (e.g., Clarkson et al. 2011) and the mean age is $\sim 10$ Gyr
(e.g., Freeman 2008), suggesting that the clusters are either real tenants of
the bulge or, alternatively, intruders originating from the halo (e.g., Forbes
& Bridges 2010; Massari et al. 2019; Minniti et al. 2021a; Romero-Colmenares
et al. 2021).
In conclusion, we confirm the OC nature for Kronberger 100, while we classify
Kronberger 119 and Kronberger 143 as old OCs based on their comparably young
ages and their relative co-movement with the surrounding stellar field,
although a classification as young GCs cannot be ruled out. For the same
reasons, ESO 92-18, the most populated cluster analysed, is also categorised
as old OC or young GC. Five objects are classified as GCs based on our
findings: Patchick 125 and Riddle 15 are classified as a metal-poor GCs,
Patchick 126 and Gaia 2 as GCs of intermediate metallicity, and Ferrero 54 as
metal-rich GC. Finally, we cautiously categorise three objects with poorly
constrained ages (Kronberger 99, Patchick 122 and FSR 190) as GC candidates.
We note that in all cases, deeper Hubble space telescope (HST) or James Webb
space telescope (JWST) observations as well as spectroscopic observations are
desired in order to build complete catalogues of likely cluster members,
improving the structural parameters and luminosities.

###### Acknowledgements.

We gratefully acknowledge the use of data from the ESO Public Survey program
IDs 179.B-2002 and 198.B-2004 taken with the VISTA telescope and data products
from the Cambridge Astronomical Survey Unit. ERG acknowledges support from
ANID PhD scholarship No. 21210330. D.M. gratefully acknowledges support by the
ANID BASAL project FB210003. This work has made use of data from the European
Space Agency (ESA) mission Gaia (http:/www.cosmos.esa.int/gaia), processed by
the Gaia Data Processing and Analysis Consortium (DPAC,
http://www.cosmos.esa.int/web/gaia/dpac/consortium). R.K.S. acknowledges
support from CNPq/Brazil through project 305902/2019-9. J.A.-G. acknowledges
support from Fondecyt Regular 1201490 and from ANID – Millennium Science
Initiative Program – ICN12_009 awarded to the Millennium Institute of
Astrophysics MAS.

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##  Appendix A Optical images for the star clusters

Figure 12: Optical images of the sky regions centred on the star clusters
analysed in the present work: (a) Kronberger 99, (b) Kronberger 100, (c)
Kronberger 119, (d) Kronberger 143, (e) Patchick 122, (f) Patchick 125, (g)
Patchick 126, (h) ESO 92-18, (i) Ferrero 54, (l) FSR 190, (m) Gaia 2, and (n)
Riddle 15. We used DECaPS colours for most of the targets, except for Riddle
15 and FSR 190 for which we used PanSTARRS colours. We use a coverage of
$5.50^{\prime}\times 6.25^{\prime}$ for the most of the clusters, except for
FSR 190 ($11.5^{\prime}\times 13^{\prime}$).

##  Appendix B VPMs and CMDs for the cluster sample

Figure 13: VPM diagrams (Table 1). The brightest cloud represents the highest
PM probability (within a radius $<1$ mas yr-1), which indicates the presence
of the cluster, as described in Section 4.1.

Figure 14: Left and middle panels: optical Gaia EDR3 CMDs for the PM-member
stars. We fit a family of PARSEC isochrones in order to derive the
uncertainties both in the age and in the metallicity estimates. Right panel:
NIR (VVVX and/or 2MASS) CMDs for the PM-member stars. The red lines, in all
panels, depict the PARSEC isochrones with age and metallicity listed in Table
1 for each cluster. In the CMDs, the cyan areas represent over-densities,
whereas the black ones are lower-densities.

Figure 15:

Figure 16: