Confirmation and Physical Characterization of the New Bulge

Astronomy & Astrophysics manuscript no. newGCs_v28 ©ESO 2021 March 8, 2021

Conﬁrmation and physical characterization of the new bulge globular cluster Patchick 99 from the VVV and Gaia surveys E.R. Garro1, D. Minniti1, 2 M. Gómez1, J. Alonso-García3, 4, T. Palma5, L. C. Smith6, and V. Ripepi7

1 Departamento de Ciencias Físicas, Facultad de Ciencias Exactas, Universidad Andres Bello, Fernández Concha 700, Las Condes, Santiago, Chile 2 Vatican Observatory, Vatican City State, V-00120, Italy 3 Centro de Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile 4 Millennium Institute of Astrophysics, Santiago, Chile 5 Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, Córdoba, Argentina 6 Institute of Astronomy, University of Cambridge, Madingley Rd, Cambridge CB3 0HA, UK 7 INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131, Naples, Italy Received 25 August 2020; Accepted 2 March 2021

ABSTRACT

Context. Globular clusters (GCs) are recognised as important tools to understand the formation and evolution of the Milky Way (MW) because they are the oldest objects in our Galaxy. Unfortunately, the known sample in our MW is still incomplete, especially towards the innermost regions, due to the high differential reddening, extinction, and stellar crowding. Therefore, the discovery of new GC candidates and the confirmation of their true nature are crucial for the census of the MW GC system. Aims. Our main goal is to confirm the physical nature of two GC candidates: Patchick 99 and TBJ 3. They are located towards the Galactic bulge. We use public data in the near-infrared (IR) passband from the VISTA Variables in the Via Láctea Survey (VVV), VVV eXtended Survey (VVVX) and the Two Micron All Sky Survey (2MASS) along with deep optical data from the Gaia Mission DR 2, in order to estimate their main astrophysical parameters, such as reddening and extinction, distance, total luminosity, mean cluster proper motions, size, metallicity and age. Methods. We investigate both candidates at different wavelengths, allowing us to discard TBJ3 as a possible GC. We use near-IR (Ks vs. (J − Ks)) and optical (G vs. (BP − RP)) colour-magnitude diagrams (CMDs) in order to analyse Patchick 99. First, we decontaminate CMDs, following a statistical procedure, as well as selecting only stars which have similar proper motions (PMs) and are situated within 30 from the centre. Mean PMs are measured from Gaia DR 2 data. Reddening and extinction are derived by adopting optical and near-IR reddening maps, and then we use them to estimate the distance modulus and the heliocentric distance. Metallicity and age are evaluated by fitting theoretical stellar isochrones.

Results. Reddening and extinction values for Patchick 99 are E(J − Ks) = (0.12 ± 0.02) mag and AKs = (0.09 ± 0.01) mag from the VVV data, whereas we calculate E(BP − RP) = (0.21 ± 0.03) mag and AG = (0.68 ± 0.08) mag from Gaia DR 2 data. We use those values and the magnitude of the RC to estimate the distance, finding a good agreement between the near-IR and optical measurements. In fact, we obtain (m − M)0 = (14.02 ± 0.01) mag, equivalent to a distance D = (6.4 ± 0.2) kpc in near-IR and (m − M)0 = (14.23 ± 0.1) mag and so D = (7.0 ± 0.2) kpc in optical. In addition, we derive the metallicity and age for Patchick 99 using our distance and extinction values and fitting PARSEC isochrones. We find [Fe/H] = (−0.2 ± 0.2) dex and t = (10 ± 2) Gyr. −1 −1 The mean PMs for Patchick 99 are µα = (−2.98 ± 1.74) mas yr and µδ = (−5.49 ± 2.02) mas yr , using the Gaia DR 2 data. They are consistent with the bulge kinematics. We also calculate the total luminosity of our cluster and confirm that it is a low-luminosity

GC, with MKs = (−7.0±0.6) mag. The radius estimation is performed building the radial density profile and we find its angular radius 0 rP99 ∼ 10 . We also recognise seven RR Lyrae star members within 8.2 arcmin from the Patchick 99 centre, but only three of them have PMs matching the mean GC PM, confirming the distance found by other methods. Conclusions. We found that TBJ 3 shows mid-IR emissions that are not present in GCs. Hence, we discard TBJ 3 as GC candidate and we focus our work on Patchick 99. We conclude that Patchick 99 is an old metal-rich GC, situated in the Galactic bulge. TBJ 3 is a background galaxy. Key words. Galaxy: bulge – Galaxy: center – Galaxy: stellar content – Stars Clusters: globular – Infrared: stars – Surveys arXiv:2103.03592v1 [astro-ph.GA] 5 Mar 2021

1. Introduction depending on their metallicities, ages and orbits. The metal-poor GCs could be the oldest population (Barbuy et al. 2006, 2009). Globular Clusters (GCs) represent the most ancient stellar More precisely, in the Galactic bulge, they may constitute the systems in the Milky Way (MW). For this reason, they are first stellar generation whose origin could coincide with the excellent tracers of the formation and chemodynamical evolu- formation of the bulge itself or before the actual configuration of tion of the Galaxy, going from the outer halo to the innermost the bulge/bar component, examples are NGC 6522, NGC 6626 Galactic regions. In addition, they survived different dynamical and HP 1 (Kerber et al. 2018, 2019). On the other hand, the processes, like dynamical friction, disk and bulge shocking, metal-rich GCs may be the second generation in the MW evaporation that also led some ancient GCs to destruction (Muratov & Gnedin 2010). Furthermore, recent studies have (Weinberg 1994). Today, we distinguish different kinds of GCs, demonstrated that some other luminous GCs may be actually

Article number, page 1 of 13 A&A proofs: manuscript no. newGCs_v28 fossil relics of accreted dwarf galaxies, such as Terzan 5 (Ferraro 2. Observational Data et al. 2009), Liller 1 (Ferraro et al. 2020), Terzan 9 (Ernandes et al. 2019) and also Omega Centauri (Lee et al. 1999; Sollima The effects of dust become increasingly prominent towards the et al. 2008). Further, with the advent of Gaia Mission and deep centre of our Galaxy. Thus, we have to overcome problems like surveys, it is now possible to associate individual GCs with high differential reddening and extinction (e.g., Alonso-García specific merger events (e.g., Vasiliev 2019; Myeong et al. 2019; et al. 2017), which introduce systematic errors in the determi- Massari et al. 2019). nation of distances. Additionally, uncertainties in the extinction values affect the estimation of ages when isochrones are used. Also, the stellar density is very high in the inner regions and However, it seems that the frequency of the MW’s GCs crowding does not always allow to resolve individual stars. is lower than the Andromeda’s GC system (van den Bergh Further uncertainties are due to the foreground and background 2010) and the MW’s open clusters. Indeed, the total number field contamination that may alter the measurement of the total of Galactic GCs (Harris et al. 2013) is about half those of our luminosity. For these reasons, we use combinations of optical neighbour Andromeda (Barmby & Huchra 2001; Huxor et al. and near-IR data in order to substantially reduce uncertainties in 2014), and the number of Galactic open clusters is vastly higher the measurements and obtain robust results. than that of GCs (Bonatto & Bica 2010). There are a number of We analyse especially red clump (RC) and red giant branch issues that make their detection a challenging task, certainly we (RGB) stars, since they are very bright in infrared and they are still missing a number of them due to high stellar extinction allow us to estimate accurate values of reddening, extinction, and stellar crowding and very low-luminosities of some of them. distance and size for our GC candidates. Nevertheless, in the last decades, the number of star cluster candidates reported in the literature has increased significantly. Below a short description of the observational material is Indeed, recent near-infrared (IR) surveys, like the Two Micron provided. All Sky Survey (2MASS; Skrutskie et al. 2006) and the VISTA Variables in the Via Láctea Survey (VVV; Minniti et al. 2010), and mid-IR survey, like Wide-field Infrared Survey Explorer 2.1. Infrared Surveys: the VVV, VVVX and 2MASS (WISE; Wright et al. 2010) have allowed us to search for We use deep near-IR data from the VVV and VVVX Survey new GC candidates. In combination with near/mid-IR surveys, (Minniti et al. 2010; Minniti 2018), acquired with the VISTA In- optical surveys are fundamental to finding new GCs, like Gaia fraRed CAMera (VIRCAM) at the 4.1m wide-field Visible and Mission DR 2 (Gaia Collaboration et al. 2018), which provides Infrared Survey Telescope for Astronomy (VISTA; Emerson & optical photometry and proper motions (PMs). Thus, new GC Sutherland 2010) at ESO Paranal Observatory. VVV and VVVX candidates are being discovered, in particular in the Galactic data are reduced at the Cambridge Astronomical Survey Unit bulge, using both the optical and near-IR images in order to help (CASU; Irwin et al. 2004) and further processing and archiving complete the census of GCs in the MW. Examples of recently is performed with the VISTA Data Flow System (VDFS; Cross discovered GCs toward to innermost Galactic regions are VVV- et al. 2012) by the Wide-Field Astronomy Unit and made CL001 (Minniti et al. 2011), VVV-CL002 and VVV-CL003 available at the VISTA Science Archive1. We use preliminary (Moni Bidin et al. 2011), Camargo 1102, 1103, 1104, 1105 data from VIRAC (Smith et al. 2018) version 2, described in and 11061 (Camargo 2018), Camargo 1107, 1108 and 1109 detail in Smith et al. (in preparation).In summary, VIRAC v2 (Camargo & Minniti 2019), and several tens of candidates in is based on a psf fitting reduction of VVV and VVVX images Minniti et al. (2017); Minniti et al. (2017a,b) and Palma et al. using DoPhot (Schechter et al. 1993; Alonso-García et al. (2019). Even so, the nature of some new GC candidates has yet 2012, 2018). Their astrometry are calibrated to the Gaia DR 2 to be confirmed and main parameters have still to be estimated. (Gaia Collaboration et al. 2018) astrometric reference system, and their photometry are calibrated against 2MASS using a globally optimised model of frame-by-frame zero points plus an In this paper, we focus on two recently discovered and not illumination correction. The VVV and, in particular, the VVVX yet well characterised GC candidates, Patchick99 and TBJ 3 Surveys are sampling the Galactic bulge and the Southern (a.k.a. TJ 3). We are studying for GC candidates in order to Galactic Plane, using the J (1.25 µm), H (1.64 µm)), and K investigate the GC luminosity function in the Galactic bulge, s (2.14 µm)) near-IR passbands, aiming to better disentangle and especially at very faint luminosities. For that purpose, Patchick characterise the stellar populations located at these low latitude 99 and TBJ 3 were selected from Bica et al. (2018), who regions. The VISTA Telescope tile field of view is 1.501 deg2, compiled a list of 10,000 good star cluster candidates in the hence 196 tiles are needed to map the bulge area and 152 tiles MW, as they had not been studied before. We use a combination for the disk. Adding some X and Y overlap between tiles for a of optical and near-IR catalogues, aiming on having a more smooth match, the area of our unit tile covered twice is 1.458 complete information about them. Our main goals are to confirm deg2. Specifically, Patchick 99 is located in the VVV tile b251, their true nature as GC and estimate their main parameters for whereas TBJ 3 is situated in the VVVX tile b462. the first time, such as reddening, distance modulus, heliocentric distance, size, total luminosity, mean cluster proper motions, metallicity and age. In addition, we use 2MASS data (Skrutskie et al. 2006; Cutri et al. 2003). It is a near-IR Survey of the sky in J (1.25 µm), H (1.65 µm) and Ks (2.17 µm) passbands. We adopt it specifically In Section 2, the observational data are briefly described. In to extend the RGB VVV colour-magnitude diagrams (CMDs), Section 3 we focus our attention to TBJ 3. Section 4 presents as these stars are saturated for Ks < 11 mag in VVV images. the methods used to estimate the physical parameters and the We downloaded the 2MASS data from the VizieR Online Data resulting values for Patchick 99. In Section 5, a summary and conclusions are drawn. 1 http://horus.roe.ac.uk/vsa/

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Catalogue 2, and we merge it with the VVV catalogue, including all stars located within 100 from the targets centres. How- ever, since the magnitude scale is diﬀerent in the two photometric systems, we have transformed the 2MASS photometry into the VVV magnitude scale 3.

2.2. Optical Surveys: Gaia DR 2 The Gaia astrometric mission maps the MW at optical wavelengths, with the aim of revealing motions, composition, formation and evolution of the Galaxy. It provides very accurate position, PMs and radial velocity measurements for sources both in our Galaxy and throughout the Local Group. We use Gaia DR 2 data (Gaia Collaboration et al. 2018) for both stellar cluster candidates, downloaded from the VizieR Online Data Catalogue. Gaia DR 2 data have been prepared by the Gaia Data Processing and Analysis Consortium (DPAC) and contain G-band magnitudes for over 1.6 × 109 sources with G < 21 mag and broad- band colours GBP (330-680 nm) and GRP covering (630-1050 nm) for 1.4 × 109 sources. PM components in equatorial coordinates are available for 1.3 × 109 sources, with an accuracy of − − − 0.06 mas yr 1, 0.2 mas yr 1, and 1.2 mas yr 1, for sources with Fig. 1. Finding charts of TBJ 3, adopting different Surveys: 2MASS G < 15 mag, G ∼ 17 mag, and G ∼ 20 mag, respectively. We K-band (a), ALLWISE w3 (b), ALLWISE w4 (c), Spitzer MIPS24 (d). use the parallax (plx) values to make the first cut in such a way to exclude clear nearby foreground stars (those with large errors might scatter to plx < 0.5 mas). In our analysis, we did not make images (Kronberger et al. 2006, 2012), so their discovery and any Gaia photometric or colour cuts. nomenclature take precedence. This cluster, which is named after the researcher who discovered it, was then listed in the compilation of Bica et al. (2018), but has not been studied in 3. TBJ 3: background galaxy detail, and we therefore decided to investigate its nature and TBJ 3 is situated at Equatorial coordinates R.A. = 17h18m14s measure its physical parameters with the VVV data. and DEC = −27d54m15s (J2000) and Galactic coordinates l = 357◦.9299 and b = 5◦.0084. It was mentioned for the first time as a GC candidate in the list of Terzan & Bernard 4.1. Statistical and PM decontamination procedures (1978) and Terzan & Ju (1980) with the name TJ 3. Sub- sequently, it was spectroscopically studied by Bica et al. Contamination by Galactic bulge and disk stars is relevant, (1998), who rename it as TBJ 3. We believe it to be the same so we have made some selections in order to decontaminate object, although in those works the Equatorial coordinates the CMDs. As mentioned in Section 2.2, we consider only are R.A.(1950) = 17h15m06s and DEC(1950) = −27◦510, stars that have plx < 0.5 mas, in order to exclude foreground that correspond to R.A.(J2000) = 17h17m05.17s and stars. Moreover, Figure 3 shows the VVV near-IR CMDs of 0 DEC(J2000) = −27d47m49.22s, different from those consid- a 3 radius region centred on Patchick 99 compared with the ered in this paper. CMD of a nearby background region, and with the statistically decontaminated CMD. This last CMD was constructed From Figure 1, it is clear that there is an object at these coor- following the procedure described by Piatti & Bica (2012) as dinates. Analysing it at different wavelengths and by looking es- applied by Palma et al. (2016, 2019) and Minniti et al. (2017). pecially at the WISE satellite images, we noted that TBJ 3 shows We notice clearly the presence of the cluster RGB and RC diffuse mid-IR emission, which is not present in GCs. This fea- that remain in the decontaminated diagram, suggesting that a 0 ture, as well as the oblate and very elliptical shape, lead us to distance of 3 from the centre is an excellent compromise for discard TBJ 3 as a possible GC candidate, and consider this to our selection. However, there are some blue stars outside of be a background galaxy. the cluster RGB that probably belong to the foreground MW disk population that persist in this CMD. Therefore, we decided to use the PMs as an independent method to decontaminate 4. Confirmation of Patchick 99 as a new GC the CMD for this cluster, since stars with similar PMs ensure belonging to the same cluster. In fact, we compared the vector Patchick 99 is located in the Galactic bulge at Equatorial coor- PM (VPM) diagram for our cluster, including stars in the 30 dinates R.A. = 18h15m47s and DEC = −29d48m46s (J2000) radius region and for the field stars, located between 4 < r < 5 and Galactic coordinates l = 2◦.4884 and b = −6◦.1452 (Figure arcmin away from the cluster centre (Figure 4). Visually, the 2). We found this cluster during our VVV search (Minniti et al. main difference between the two PM distributions is that in the 2017; Minniti et al. 2018; Minniti 2018), but later realized that case of our cluster selection, this one shows two over-densities, an object at that position had been reported before as part of suggesting a bimodal distribution, unlike the field stars that the deep sky hunters (DHS) survey of the DSS and 2MASS show a shallower homogeneous distribution when we move 2 https://vizier.u-strasbg.fr/viz-bin/VizieR away from the centre of the cluster, indicating an unimodal 3 http://casu.ast.cam.ac.uk/surveys-projects/vista/technical/photometric- distribution. In order to confirm our statement we have carried properties out the Gaussian mixture modelling (GMM) analysis (Muratov

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Fig. 2. Finding chart of Patchick 99 showing from left to right the central 1.60 × 1.10 optical colour images from PanStarrs, and near-IR colour images from the VVV and 2MASS surveys.

Fig. 3. Observed VVV near-IR CMDs of a 30 radius region centred on Patchick 99 (left), of a background region with similar area (middle), and statistically decontaminated CMD (right) following the procedure described by Palma et al. (2016, 2019). We note the clear presence of the cluster RC in the decontaminated diagram.

& Gnedin 2010), which helps to give us the statistical signifi- we can confirm that the distribution of field stars located away cance of an unimodal versus a bimodal distribution. We have from the cluster centre is unimodal since the D < 2 and the performed the GMM analysis with the heteroscedastic statistic standard deviation of the second mode is of σ2 ≈ 14, which is for each sample. In summary, we perform the GMM analysis for not physical. About the 30 radius region sample, the analysis our three subsamples: the field stars located between 4 < r < 5 becomes more complicated. We believe that the two peaks arcmin away from the Patchick 99 centre, the position selection have a very small separation and the method is not able to including all stars situated within 30 from the cluster centre, and distinguish both properly, indeed comparing the parameters of our PM selection. Firstly, we do this for field stars and position the first Gaussian with the second one we can appreciate that the selection in order to obtain the statistical significance for the first dominates over the second. On the other hand, the GMM two Gaussian distributions shown in Figure 4. Subsequently, method on the PM selection indicates a bimodal distribution, we run the GMM algorithm to distinguish the two Gaussian since D > 2. This may be misleading to interpret since we peaks shown in Figure 5. The statistical parameters are shown should have expected an unimodal distribution for the stars in in Tables 2 and 3. For a mixture of two normal distributions the a cluster. However, we have to highlight that any sample will means and standard deviations along with the mixing parameter be contaminated by foreground stars that will have different (D, separation of the means relative to their widths) are usually velocity (and PM) distribution. Thus, having two peaks in the used, as a total of five parameters. Ashman et al. (1994) noted sample of PM selection is not unexpected. In any case, this does that D > 2 is required for a clean separation between the modes, not represent a problem since the second mode is very narrow while if the GMM method detects two modes, but they are not and is not dominant over the first, meaning that our final sample separated enough (D < 2), then such a split is not meaningful. has got a very small contamination. Applying the GMM analysis to our samples we noted that they may show a bimodal distribution, but with a low significance Successively, we calculate the mean cluster PMs (adopting level. Doing a deep analysis of the GMM resulting parameters, the σ-clipping method) measured from Gaia DR 2, yielding

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−1 −1 µα = (−2.98 ± 1.74) mas yr and µδ = (−5.49 ± 2.02) mas yr , which are in good agreement with the PM values found by the GMM method. After that, we selected as cluster members only stars within 3 mas yr−1, following the procedure of Garro et al. (2020), indicated by the black circle drawn in Figure 4. Also, the size of the circle is set taking into consideration the typical size of GC members in the VPM diagram for other well studied MW bulge GCs. Additionally, in Figure 5 we show the −1 PM distributions in a wide range (−20 < µα < 15 mas yr and −1 −20 < µδ < 10 mas yr ), considering only stars situated within 30 from the Patchick 99 centre (blue histogram), attempting to minimise field stars. The resulting star sample after the PM cut is shown with the red histogram. Each histogram is constructed considering the sum of all the combined values per unit bin, selecting a fixed bin size of 0.8 mas yr−1 (value that allowed us to visually distinguish the two peaks of the Gaussian distributions). We can appreciate double peaked distributions for both blue histograms, with a very little separation (as expected from the GMM method), suggesting that we have at least two overlapping populations: the bulge field stars and the star cluster. Indeed, fitting two Gaussian distributions we assign a narrower and more peaked distribution for Patchick 99 (green curve) and a wider distribution for Bulge field stars (grey curve). The total distribution (black curve) is obtained by coadding the two Gaussians, in order to fit the entire sample. Figure 6 displays the PM decontaminated CMDs for VVV and Gaia data. We can recognise that the main GC features, like RGB and RC, remain but, in comparison with the statistical decontamination (Figure 3), the foreground disk population is now better removed.

Following these procedures, we have obtained the decontaminated near-IR (Ks versus J − Ks) and optical (G versus BP − RP) CMDs for our cluster, as shown in the right panels of Figures 6 and in Figure 7. We use those CMDs to derive the cluster’s main parameters. Both diagrams clearly show the RC at Ks = (12.5 ± 0.04) mag and G = (15.5 ± 0.05) mag, suggesting that P99 is a metal-rich GC. It is crucial to use RC stars in this kind of studies, because these stars are very good distance indicators.

Fig. 4. Top panel: VPM diagram from Gaia DR 2 dataset for star mem- 4.2. Estimation of Physical Parameters for Patchick 99 bers located within 30 from the Patchick 99 centre. The black circle −1 Nowadays, a wide range of reddening maps already exist, indicates the position of the cluster selection within 3 mas yr . Bottom panel: VPM diagram for field stars located at 4.80 from the Patchick such as Schlafly & Finkbeiner (2011), Gonzalez et al. (2011, 99 centre. In each panel, colour represents density, with magenta the 2018), Minniti et al. (2018), Soto et al. (2019), Saito et al. highest, followed by blue, green and red. (2020). We estimate the reddening and the extinction toward this GC following Ruiz-Dern et al. (2018) and we benefit from the clear position of the RC in the CMDs. We adopt also E(BP − RP) = AG/3.12 = (0.21 ± 0.03) mag (Cardelli the intrinsic RC magnitude MKs = (−1.605 ± 0.009) mag and et al. 1989; O’Donnell 1994). Therefore, the resulting clus- the intrinsic colour (J − Ks)0 = (0.66 ± 0.02) mag. Using the ter distance modulus from the Gaia optical photometry is latter, we calculate a color excess of E(J − Ks) = (0.12 ± 0.02) (m − M)0 = (14.23 ± 0.1) mag and the distance D = (7.0 ± 0.2) mag, in accordance with the adopted reddening map, and kpc, agrees within 3σ with our near-IR distance. the extinction AKs = 0.72 × E(J − Ks) = (0.09 ± 0.01) mag (Cardelli et al. 1989). Consequently, we use these values in Using our estimates of the reddening and distance we were order to determine distances, so we measure a distance modulus able to fit PARSEC4 isochrones (Bressan et al. 2012; Marigo (m − M)0 = (14.02 ± 0.01) mag equivalent to a heliocentric et al. 2017) to the CMDs of Patchick 99. This allows us to have distance D = (6.4 ± 0.2) kpc. estimation of the metallicity and the age of the GC, finding Similarly, for optical wavebands we identify again RC stars and [Fe/H] = (−0.2 ± 0.2) dex and t = (10 ± 2.0) Gyr, respectively. adopt the intrinsic RC magnitude MG = (0.459 ± 0.009) In order to obtain a more robust result, we have also derived the mag (Ruiz-Dern et al. 2018). The near-IR extinction metallicity from the slope of the RGB (α = 0.11±0.01) using the

AKs = (0.09 ± 0.01) mag corresponds to the optical ex- 4 tinction AG = 0.86 × AV = (0.68 ± 0.08) mag, deriving http://stev.oapd.inaf.it/cgi-bin/cmd

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Fig. 6. Observed (left panels) and PM decontaminated (right panels) CMDs for the globular cluster Patchick 99 , employing the near-IR VVV (top panels) and optical Gaia DR 2 data (bottom panels).

Fig. 5. PM distributions in RA (top panel) and in DEC (bottom panel), for stars located within 30 from the Patchick 99 centre (blue histogram) and for our cluster PM selection (red histogram). Grey and green curves are the Gaussian distributions for the Bulge field stars and Patchick 99 stars, respectively. The total distribution, obtained by coadding the two Gaussian distributions, is fitted as black curve. Fig. 7. The VVV near-IR (left panel) and Gaia DR 2 optical (right panel) PM decontaminated CMD for the globular cluster Patchick 99. The red calibration of Cohen et al. (2016), finding [Fe/H] = −0.3 ± 0.2 dotted line is fitted by a PARSEC isochrone with age 10 Gyr and metal- dex, in agreement with our original estimate. Figure 7 shows a licity [Fe/H] = −0.2 dex. The magenta points represent the position of good fit of the isochrones with the above mentioned values of RR Lyrae star members in the near-IR CMD. metallicity and age in both our optical and near-infrared CMDs. We determined the errors in age and in metallicity by changing the isochrones at a fixed metallicity and a fixed age, respectively, CMDs. We include 2MASS cluster members with Ks < 11 mag, until they do not fit the cluster sequence simultaneously in the as they are more sensitive to the metallicity variations (e.g. , near-IR and optical CMDs. Therefore, it is clear that although McQuinn et al. 2019). We can see that variations in metallicity age is one of the fundamental parameters to characterise GCs, its have an especially strong effect along the RGB and RC, and correct determination is still one of the most complicated tasks vice-versa, we can notice evident changes in age in the MS-TO to perform, especially in environments with high stellar density region. For this reason our age should be taken as a crude and with differential reddening, such as the Galactic bulge. This estimate, since we are unable to measure it precisely. is mainly due to difficulties to reach the main sequence turn-off (MS-TO) point. We can appreciate that problem in Figure 8, All of the previously derived parameters, including position, which displays the VVV and 2MASS PM decontaminated metallicity and kinematics confirm that Patchick 99 is a bulge

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Therefore, estimating the MV diﬀerences and assuming the similarities between the GCs, we derive that the total luminosity for Patchick 99 is MV = −5.2 mag, ∼ 2.2 less luminous of the MW GC luminosity function peak (MV = (−7.4 ± 0.2) mag from Harris 1991; Ashman & Zepf 1998)

All these parameters are summarised in Table 1.

Fig. 8. Fitting of isochrones, in the VVV CMDs, at fixed metallicity of [Fe/H] = −0.2 dex and variation in ages t=8, 9, 10, 11, 13 Gyr (right panel); while at fixed age of t=10 Gyr and different metallicities [Fe/H] = 0, −0.1, −0.2, −0.3, −0.4 dex (left panel). Black points represent the VVV cluster members, whereas blue points are those from Fig. 9. Gaia+VVV optical-near-IR CCDs for Patchick 99, as density 2MASS catalogue. plot. On the left: squares are the observed stars, using the entire catalogue without selection cuts; on the right: circles represent star members of Patchick 99, considering bright stars previously selected. At the GCs, but if we consider its age, it could be even younger than top-left of the panel, the red arrow represents the reddening vector. typical metal-rich GCs present in the Galactic bulge, which have ages between 12 and 13 Gyr (e.g., Carretta et al. 2000. However, many studies have demonstrated that GCs show a relatively wide range of ages in the bulge (Zoccali et al. 2003; Clarkson 4.3. The derivation of the surface density profile et al. 2011; Valenti et al. 2013; Bernard et al. 2018). A detailed description of the structural parameters of Patchick 99 would need a careful treatment of completeness as well as rel- Figure 9 shows the Gaia+VVV optical-near-IR colour- atively large numbers of member stars from which a radial colour diagram (CCD) for the whole catalogue without selection profile can be derived. Traditionally, King profiles (King 1962) cuts, and for only cluster members of Patchick 99 with Ks < 15 have been fitted to a significant fraction of MW old clusters, mag. We can clearly notice that the colour distribution reveals with however more and more evidence that other profiles might a tighter sequence for star members (circles, right panel) than provide better fits, especially when extragalactic or massive GCs for the field stars (squares, left panel). In particular, we can are included (e.g., Mackey & Gilmore (2003), de Boer et al. appreciate that there is a little differential extinction, in the right (2019a)). Although rich clusters allow for model-dependent panel of Figure 9. Based on the high resolution reddening map sizes and structural properties, our sample of member stars by Surot et al. 2020, the mean reddening is E(J − Ks) = 0.05 is not enough to adequately address a comparison among the mag in this field, which differs from our reddening value by different models available. Instead, a King function is assumed ∆(E(J − Ks)) = 0.07 mag at most. Hence, we believe that to be a good approximation for the radial distribution of the our estimation is in good agreement with the adopted map, stellar density. discarding this as a significant problem. The correct determination of the cluster centre has a fun- Finally, we derive the total luminosity of our cluster, damental importance, since an error in its position can lead to using the catalogue with only cluster members. Once the flux altered results regarding the density profile. For this reason, we for each star is measured, we derive the absolute magnitude have used the K-Means algorithm in Python to determine the from the total flux, obtaining MKs = (−7.0 ± 0.6) mag, centre in a robust way from our catalogue of cluster member equivalent to MV = (−4.5 ± 0.8) (for a typical GC colour of stars. In summary, this is a machine-learning algorithm that (V − Ks) = (2.5 ± 0.5) mag), indicating that it is a very faint GC. searches for subgroups (or literally "clusters") in a given param- This value is an underestimate of the total luminosity, since the eter space among a sample of data points. We checked visually faintest stars are missing. Regarding this, we compared Patchick that the resulting centres were close to the expected density 99 luminosity with that other known GCs similar to Patchick peaks and we found that the initial position (R.A. = 18h15m47s 99 in metallicity: NGC 6553 ([Fe/H] = −0.18 dex; D = 6.01 and DEC = −29d48m46s (J2000)) coincides almost-perfectly kpc; MV = −7.77 mag), NGC 6528 ([Fe/H] = −0.11 dex; with the resulting values of the centre, with a small separation 00 00 D = 7.9 kpc; MV = −6.57 mag) and Terzan 5 ([Fe/H] = −0.23 of ∆RA ≈ 2 and ∆DEC ≈ 5 . dex; D = 5.9 kpc; MV = −7.42 mag). Using the same Starting from these new coordinates, we divided our sample of method, and also spanning on the same magnitude range member stars into ten circular annuli, out to a radius of 1.50, in 0 (10.7 < Ks < 17.2), we derive the integrated near-infrared abso- steps of 0.15 . We do not need to apply geometric corrections as lute magnitude for each GC, finding MKs (NGC 6553) = −9.5 the resulting circular annuli are within the FOV of our catalogue. mag, MKs (NGC 6528) = −8.0 mag and MKs (Ter5) = −9.6 We performed the radial density profile of Patchick 99 (see mag. We converted them in V−band and scaled to the MV Figure 10) dividing the total number of stars in each radial bin values from the 2010 version of the Harris (1996) catalogue. by the area of that ring in order to derive the density in each bin.

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Poisson errors are also shown. We note that the error bars are of the GC, type for each source and their PMs. relatively large, mainly due to the low-number statistics in each radial bin, especially in the innermost point (see Figure 10). No Initially we constructed their phased light curves, in order background has been subtracted since we are dealing with a to discriminate their pulsation mode. We identify 13 fundamen- list that is expected to be free from foreground stars and other tal mode pulsators (ab-type RR Lyrae stars) with long periods contaminants. (P & 0.4 days) and large amplitudes, and 8 first-overtone pulsators (c-type RR Lyrae stars), with short period (P . 0.4 days) We have overplotted a family of King profiles adopting dif- and small amplitudes. The RRc and RRab pulsators also differ 0 0 0 ferent values of core radius (rc = 1.8 , 1.5 , 1.2 ), but keeping in the morphology of their light curves, since the RRab’s have the tidal radius fixed at 100. The choice to use that value of tidal typically asymmetrical light curves, unlike RRc’s. Figure 11 dis- radius is justified following de Boer et al. (2019b) (see their Fig- plays the Amplitude-Period diagram (so-called Bailey diagram, ures 13 and 14), where a clear correlation between the tidal ra- Bailey et al. 1919) in such a way to highlight that differences. dius and galactocentric radius of a given GC is illustrated. As Indeed, we consider the Bailey diagram a solid tool for verifying shown in Figure 10, the observational points are best represented our estimations. 0 by rc = 1.2 , which is equivalent to rc ∼ 1.1 pc. Also, we con- 0 sider the tidal radius rt = 10 as the size of the cluster, which corresponds to a physical size of 9.3 pc.

Fig. 10. Radial surface density of Patchick 99 (black points), taking into consideration only PM selected member stars. The coloured lines are King model profiles that best reproduce observational data, with a Fig. 11. Bailey diagram for detected 21 RR Lyrae stars (black points), fixed value of the tidal radius 100 and different values of core radius, in situated within 12 arcmin from the Patchick 99 centre, while we high- cyan r = 1.80, in red r = 1.50 and in blue r = 1.20 Poisson errors are c c c light the RR Lyrae member stars with magenta points. shown as error bars.

Our main goal is to identify which RR Lyrae stars are real 4.4. The RR Lyrae stars in Patchick 99 members of Patchick 99. Firstly, we measured their projected distance from the centre using the centroid of each variable stars. RR Lyrae variable stars represent a very old-population in our Based on these distances and considering the size of the cluster, Galaxy, found in the Galactic halo and bulge. In particular, we believe that seven RR Lyrae stars are members of Patchick according to Pietrukowicz et al. (2015) their spatial density 99, as shown in Figure 12 and evidenced by a star symbol in ranges between 80 and 440 RRL/deg2 in the bulge. Table 4. In addition, we compare their projected distance with They are also considered powerful tools to reveal the nature the resulting heliocentric distance (Figure 12), confirming again of a GC candidate because if detected in a stellar cluster, RR the membership. In detail, we used the period-luminosity (PL) Lyrae stars guarantee that it is an old GC. Although these relation in Ks-band following Muraveva et al. (2015) (with RRc variables are used as excellent tracers of old and metal-poor stars “fundamentalized” by adding 0.127 to the logarithm of the populations, there are observational evidences that suggest the period) in order to derive their heliocentric distance. Once se- presence of RR Lyrae also in metal-rich GCs, such as NGC 6388 lected the RR Lyrae members, we estimate the mean distance, ([Fe/H] = −0.44 dex) and NGC 6441 ([Fe/H] = −0.46 dex) finding a value of D = 7.06±0.48 kpc, consistent with the helio- (Pritzl et al. 2002; Clementini et al. 2005), and NGC 6440 centric distances obtained from the VVV and Gaia photometries [Fe/H] = −0.36 dex), all of which are somewhat more metal- (see Section 4), since these values differ by less than 2σ. On the rich than Patchick 99. Additionally, they are good reddening other hand, we discard the others as members since they have and distance indicators. heliocentric distances larger than those found using VVV near- IR photometry, or they are located outside our assumed tidal For these reasons, we have searched for these variable stars radius. However, we can restrict the RR Lyrae sample to the and we have detected 21 RR Lyrae stars within 12 arcmin from ones that have PMs matching the mean GC PM within the er- the Patchick 99 centre, matching the OGLE (Soszynski´ et al. rors, we find that only 3 of them fulfil this requirement: OGLE- 2014), the VVV (Majaess et al. 2018) and the Gaia (Clementini BLG-RRLYR-35312, 35476 and 35459, favouring a short dis- et al. 2019) catalogues. They are listed in Table 4, where we tance of 6.3 ± 0.5 kpc in the mean. Additionally, Figure 12 summarised: identification, location, period, photometry in does not show OGLE-BLG-RRLYR-35364 and OGLE-BLG- different filters, heliocentric distance, distance from the centre RRLYR-35381, since their distance values are very large and

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Fig. 12. Spatial distribution of RR Lyrae variable stars detected within Fig. 13. MKs − log(P) diagram for all RR Lyrae sample (black points) 120 from the centre of Patchick 99. The magenta points represent the and RR Lyrae star members (magenta points, while the squares repre- seven RR Lyrae stars considered cluster members, whereas we highlight sent the PM variable members). Blue and red lines represent the least- the PM members with magenta squares. The distance errorbars are of squares fit for all RR Lyrae sample and cluster members, respectively. 0.5 kpc for each point. The dotted line depicts the heliocentric distance at D = (6.4 ± 0.2) kpc derived from the VVV near-IR photometry. pulsation period (see their Figure 1 and 2). Also, from the observational point of view, we have compared probably they are located in the Galactic halo or in the Sagittar- the location of our RR Lyrae with those confirmed PM members ius dwarf galaxy. We also tested two other PL relations from of the cluster NGC 6441 from Alonso-García et al. (in prepa- Gaia Collaboration et al. (2017) and Navarrete et al. (2017), ration). The RR Lyrae stars in Patchick 99 fall in the expected yielding slightly larger distance values. However, we use the region of the near- IR CMD for this metal-rich cluster. In any comparison between the three PL relations, in order to assign case, spectroscopic metallicities are needed to confirm if this is a mean distance error of 0.5 kpc. Once absolute magnitudes are the most metal-rich GC known with RR Lyrae. obtained, we also build-up the PL relation diagram (Figure 13). This allowed us to confirm again the membership, since we find 5. Summary and Conclusions a stronger relation when the least-square fit is used on the star cluster members (red line), rather than on the whole sample (blue We have investigated the GC candidates Patchick 99 and TBJ 3 line). We also show the VVV phased light curves for each RR in order to understand their real nature. Lyrae member (Figure 14). We note that the light curve profile They are analysed in optical and near-IR wavelengths with the for OGLE-BLG-RRLYR-35459 is slightly worse than the oth- goal of determining their physical parameters. The visual exam- ers, since this variable appears a bit blended. ination of TBJ 3 at various wavelengths confirms that it is not a Moreover, we derive the expected spatial density from GC but from its mid-IR emission we conclude that TBJ 3 is a Pietrukowicz et al. (2015) and Navarro et al. (2020). Specifi- background galaxy. cally, following Navarro et al. (2020), we are able to predict a Therefore, we have focused our work on Patchick 99. We have mean density of 4 field RR Lyrae type-ab in the same field of measured its reddening, extinction, distance modulus and helio- Patchick 99. We found 21 variables in total, including 13 RRab. centric distance, size, proper motion, total luminosity, metallicity Hence, this value represents a clear excess over the background and age. We summarised all those values in Table 1. (∼ 4.5σ detection). Even though the field contamination is severe, we used two dif- Finally, the magenta points in Figure 7 define the position ferent methods (statistical and PM decontamination) recovering of the seven RR Lyrae stars in the VVV CMD. Their near-IR the same results, with the GC RGB and RC clearly present. We magnitudes are on average much fainter than the RC (∼ 1 − 1.5 conclude that Patchick 99 is a metal-rich GC, located in the mag). However, both theory and observations suggest that the Galactic bulge at a heliocentric distance of D = 6.6 ± 0.6 kpc, RR Lyrae indeed should be fainter than the RC in the near- obtained as an average distance of three-independent methods IR CMDs and also indicate that more metal-rich RR Lyrae are (Gaia DR 2 and VVV photometries, and three RR Lyrae star fainter than metal-poor ones. For example, Cassisi et al. (2004) members). We define it as a genuine GC because both CCD and explored the predicted behavior of the pulsators as a function CMDs yield a population with an age of 10 Gyr. These results of the horizontal branch morphology and over the metallicity are confirmed by the presence of seven RR Lyrae stars, located range Z=0.0001 to 0.006, finding that the RR Lyrae luminos- at d < 120 from the cluster centre and at the same distance of the ity decreases with increasing metallicity. Further, Marconi et al. cluster from the Sun. However, analysing their PM we can con- (2018) constructed new sets of helium-enhanced (Y = 0.30, firm that three of them are surely member of our cluster: OGLE- Y = 0.40) nonlinear, time-dependent convective hydrodynami- BLG-RRLYR-35312, 35476 and 35459, since their PMs match cal models of RR Lyrae stars covering a broad range in metal the mean cluster PM within the errors. Patchick 99 may be the abundances (Z = 0.0001 – 0.02), finding that an increase in he- most metal-rich globular cluster with RR Lyrae, to be confirmed lium content from the canonical value (Y = 0.245) to Y = 0.30 – by spectroscopic observations. As mentioned previously, even 0.40 causes a simultaneous increase in stellar luminosity and in if position, metallicity and kinematics confirm that it is a bulge

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GC, the age of Patchick 99 is a few Gyr younger than the typical Irwin, M. J., Lewis, J., Hodgkin, S., et al. 2004, in Optimizing Scientiﬁc Re- age of metal-rich GCs (∼ 12 − 13 Gyr) in the same regions. In turn for Astronomy through Information Technologies, ed. P. J. Quinn & any case, it is even important to underline that our estimation of A. Bridger, Vol. 5493, International Society for Optics and Photonics (SPIE), 411 – 422 age is quite rough and we need deeper observations to be more Kerber, L. O., Libralato, M., Souza, S. O., et al. 2019, Monthly Notices of the accurate. Royal Astronomical Society, 484, 5530 Another important conclusion is that Patchick 99 is a low- Kerber, L. O., Nardiello, D., Ortolani, S., et al. 2018, The Astrophysical Journal, 853, 15 luminosity GC (MKs = −7.0 mag), suggesting that many other King, I. 1962, AJ, 67, 471 faint GCs are still to be revealed in the bulge of the Milky Way. Kronberger, M., Reegen, P., Alessi, B. S., Patchick, D., & Teutsch, P. 2012, As- Acknowledgements. We gratefully acknowledge the use of data from the ESO trophysics and Space Science Proceedings, 29, 105 Public Survey program IDs 179.B-2002 and 198.B-2004 taken with the VISTA Kronberger, M., Teutsch, P., Alessi, B., et al. 2006, A&A, 447, 921 telescope and data products from the Cambridge Astronomical Survey Unit. Lee, Y. W., Joo, J. M., Sohn, Y. J., et al. 1999, Nature, 402, 55 ERG acknowledges support from an UNAB PhD scholarship. D.M. acknowl- Mackey, A. D. & Gilmore, G. F. 2003, Monthly Notices of the Royal Astronom- edges support by the BASAL Center for Astrophysics and Associated Tech- ical Society, 338, 85 nologies (CATA) through grant AFB 170002. D.M. and M.G. are supported Majaess, D., Dékány, I., Hajdu, G., et al. 2018, Astrophysics and Space Science, by Proyecto FONDECYT No. 1170121. 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Table 1. Main physical parameters for Patchick 99 determined using near-IR and optical datasets.

Physical parameters Patchick 99 RA (J2000) 18h15m47s DEC (J2000) -29d48m46s Latitude 2◦.4884 Longitude −6◦.1452 µα [mas/yr] −2.98 ± 1.74 µδ [mas/yr] −5.49 ± 2.02

AKs [mag] 0.09 ± 0.01 AG [mag] 0.68 ± 0.08 E(J − Ks) [mag] 0.12 ± 0.02 E(BP − RP) [mag] 0.21 ± 0.03 (m − M)0 [mag] 14.02 ± 0.04 Dmean [kpc] 6.6 ± 0.6

MKs [mag] −7.0 ± 0.6 MV [mag] −5.2 [Fe/H] [dex] −0.2 ± 0.2 Age [Gyr] 10.0 ± 2 rc [arcmin] 1.2 (1.1 pc) rt [arcmin] 10 (9.3 pc)

Table 2. GMM analysis for each sub-sample (ﬁeld stars, position and PM selection) applied to PM in RA. The subscripts 1 and 2 indicate the ﬁrst and second mode of the Gaussian distribution.

µ1 σ1 µ2 σ2 D [mas yr−1] [mas yr−1] [mas yr−1] [mas yr−1] Field stars −2.11 ± 0.11 4.41 ± 1.98 −1.26 ± 0.52 13.99 ± 1.98 0.08 ± 0.05 Position sel. −1.96 ± 0.58 4.08 ± 2.8 −2.54 ± 0.55 10.71 ± 3.16 0.07 ± 0.06 PM selection −3.35 ± 0.13 1.42 ± 0.05 −0.73 ± 0.14 0.53 ± 0.08 2.46 ± 0.09

Table 3. GMM analysis for each sub-sample (ﬁeld stars, position and PM selection) applied to PM in DEC. The subscripts 1 and 2 indicate the ﬁrst and second mode of the Gaussian distribution.

µ1 σ1 µ2 σ2 D [mas yr−1] [mas yr−1] [mas yr−1] [mas yr−1] Field stars −4.61 ± 0.11 4.4 ± 0.2 −3.53 ± 0.57 13.63 ± 0.85 0.11 ± 0.06 Position sel. −4.51 ± 0.11 3.52 ± 0.21 −4.09 ± 0.41 7.05 ± 0.54 0.08 ± 0.07 PM selection −6.13 ± 0.39 1.35 ± 0.16 −3.52 ± 0.41 0.8 ± 0.2 2.35 ± 0.13

Article number, page 11 of 13 A&A proofs: manuscript no. newGCs_v28

Table 4. Detected RR Lyrae stars within 120 from the Patchick 99 centre. The symbol F indicates the star members of the cluster, while the double symbols FF highlight the variable stars that have PM matching the mean GC PM within the errors. 1] − δ µ 1] [mas yr − α µ Type centre d RRL D J s K (J2000) (J2000) [day] [mag] [mag] [mag] [kpc] [arcmin] [mas yr 273.8098 -29.8325273.9633 0.4864334 -29.9070274.0053 15.47 0.2879753 -29.9212 13.84 0.5301811 15.93 14.10273.9599 15.48 14.58 6.1 -29.7208273.9885 13.77 14.82 0.5121471 -29.7488 14.16 7.9 0.5217077 15.88 8.2 6.1 15.90 14.27 RRab 5.8 14.25 14.66 7.4 14.75273.8947 7.6 -3.866 RRc -29.8940 7.6 RRab 0.6214080 5.6 -3.070 6.448 15.72 -4.627 4.6273.9749 13.91 RRab -29.8401 -14.647 14.50 RRab -4.028 0.3754443 4.453 7.1 15.50 1.692 13.98 -3.489 5.8 14.30 1.172 6.6 RRab 2.4 2.041 RRc 1.390 -3.172 -8.688 FF FF F F F F FF SourceIDOGLE-BLG-RRLYR-35312 OGLE-BLG-RRLYR-35348OGLE-BLG-RRLYR-35447 OGLE-BLG-RRLYR-35476 273.8499OGLE-BLG-RRLYR-35557 -29.9502OGLE-BLG-RRLYR-15997 0.2734252OGLE-BLG-RRLYR-16094 274.1133 16.91OGLE-BLG-RRLYR-16108 273.7959 -29.8866 15.57 RAOGLE-BLG-RRLYR-16115 -29.7434 0.6141217 15.93OGLE-BLG-RRLYR-35292 0.2933517 16.09 12.2OGLE-BLG-RRLYR-35355 274.0016 16.18 14.26 DECOGLE-BLG-RRLYR-35364 273.7955 -29.6816 14.79 14.64 10.1OGLE-BLG-RRLYR-35381 273.8588 -29.8620 0.3376222 15.13OGLE-BLG-RRLYR-35382 273.8741 -29.9444 8.3 0.2931980 RRcOGLE-BLG-RRLYR-35384 P 273.8937 -29.8688 8.7 0.5942311 - 16.64OGLE-BLG-RRLYR-35390 -29.8050 0.5927029 19.28 11.0 15.06OGLE-BLG-RRLYR-35431 -0.453 273.8970 0.6040448 14.83 18.35 17.05 9.9 15.37OGLE-BLG-RRLYR-35459 273.9015 -29.7807 RRab 16.61 V 15.08 16.51 17.53OGLE-BLG-RRLYR-35533 273.9381 -29.6619 0.7768699 9.8 14.76 -4.932 16.85 RRcOGLE-BLG-RRLYR-35535 9.4 29.4 -29.9478 0.210 0.2519186 16.00 15.22OGLE-BLG-RRLYR-35571 22.9 274.0821 0.6426197 15.26 14.17 9.5 -3.290 10.3 274.0874 -29.7864 9.5 15.90 8.6 13.98 14.67 -10.364 274.1270 -29.8810 5.5 0.3104254 14.17 14.25 RRc -29.8545 3.2 0.4767085 8.9 RRab 16.34 -9.259 RRc 14.60 0.5653381 5.7 RRab 16.07 14.96 -3.943 8.1 RRab 16.34 14.37 3.5 15.25 -4.906 -4.234 - 14.52 9.4 14.77 -1.456 9.6 8.1 -4.551 14.83 RRab 7.6 -8.455 -3.179 RRc 9.0 -3.910 RRab 8.3 -0.187 9.4 - -5.090 11.2 0.943 RRc -5.198 RRab RRab 3.183 -1.772 -1.826 -5.984 -2.534 -4.132 -2.042 -3.027

Article number, page 12 of 13 E.R. Garro et al.: Conﬁrmation of the new bulge globular cluster Patchick 99 from the VVV and Gaia surveys

Fig. 14. Phased light curves for the RR Lyrae star members of Patchick 99 GC, classiﬁed as ab-type with P > 0.4 days and c-type with P < 0.4 days.

Article number, page 13 of 13