arXiv subjects

M. C. Parisi

Publications and source records attributed to M. C. Parisi.

At least 19 recordsLinked to original sources

arXiv2025

Infrared photometry and CaT spectroscopy of the most metal-poor in-situ globular cluster VVV-CL001

Globular clusters in the Galactic bulge are difficult to study due to high extinction and severe crowding. VVV-CL001 is an old, metal-poor, and fast cluster in the inner bulge, whose extreme properties make it a key probe of the early chemical and dynamical evolution of the Milky Way. We derive its fundamental parameters by combining spectroscopy, astrometry, and near-infrared photometry. Metallicity and radial velocity were measured from medium-resolution FORS2/VLT spectra; proper motions from Gaia DR3; and FourStar/Magellan photometry was used to refine the cluster centre, derive its structure, and estimate age, distance, and reddening. VVV-CL001 is confirmed to be an old ($12.1^{+1.0}_{-1.2}$ Gyr), metal-poor ($[\text{Fe}/\text{H}] = -2.25 \pm 0.05$) cluster at a heliocentric distance of $7.1^{+1.3}_{-1.1}$ kpc, with reddening $E(J-K_s) = 1.40^{+0.01}_{-0.02}$. Its mean proper motions are $\mu_\alpha^* = -3.68 \pm 0.09$ and $\mu_\delta = -1.76 \pm 0.10$ mas yr$^{-1}$, and its radial velocity is $-334 \pm 4$ km s$^{-1}$. The orbit is eccentric ($e = 0.76^{+0.10}_{-0.14}$), confined to the inner Galaxy ($|Z|_{\max} \approx 1$ kpc) and within the bar's influence ($R < 5$ kpc), with pericentre $0.6^{+0.3}_{-0.2}$ kpc and apocentre $4.5^{+2.5}_{-1.2}$ kpc. Its old age, low metallicity, and orbital properties support an in-situ origin, identifying VVV-CL001 as one of the most metal-poor inner-Galaxy clusters formed in the early Milky Way. It likely belongs to the primordial disk cluster population later trapped by the bar, making it a fossil remnant of the earliest phases of Galactic assembly.

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arXiv2025

The VISCACHA survey XIV. Chemical evolution history of the SMC: The Southern Bridge Clusters

The chemical evolution history of the Small Magellanic Cloud (SMC) is complex and is best understood through a comprehensive analysis of star clusters across its various regions. The VISCACHA survey aims to fully explain the chemical evolution of SMC star clusters by analyzing different sub-regions adopted from an existing framework. The west halo (WH) region, which contains the oldest and most metal-poor stellar populations, exhibits a clear age-metallicity relation (AMR) with minimal dispersion. This region shows a significant dip of ~0.5 dex in metallicity approximately 6 Gyr ago. This was likely caused by a major merger event that subsequently accelerated the star formation rate. Clusters in the Southern Bridge (SB) and Northern Bridge regions of the SMC may have experienced distinct chemical enrichment histories, as suggested by our previous works but with limited data coverage. Furthermore, the AMR of wing/bridge (W/B) shows no sign of enrichment caused by the aforementioned merger event, but exhibits signatures of the recent collisions between the clouds contemporaneous with the epochs of the Magellanic Stream and Bridge formations. In this study, we present an updated AMR for the SB region based on a sample that includes approximately 67% of its known clusters. Contrary to the expectation of a very unique chemical evolution history, these SB clusters show a trend similar to the one of the WH clusters. The chemical evolution models that best fit the AMR trend of the SB clusters show excellent agreement with the major merger model proposed for the WH clusters. Building on this, we suggest a new unified chemical evolution model for both the WH and SB clusters, which can be explained by a major merger at ~6 Gyr followed by episodic chemical enrichment over time.

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arXiv2025

Multi-Wavelength characterization of VVVX open clusters

Context. Large-scale surveys across wavelengths, aided by machine learning, have improved the detection of old open clusters in high-extinction Milky Way regions. Aims. We aim to confirm or reject automatically detected open clusters in poorly studied, contaminated regions, refining samples for Galactic disk formation studies. Methods. Using VVVX, 2MASS, and Gaia DR3, we analyzed nine cluster candidates: BH118, BH144, Schuster-MWSC 1756, Saurer 3, FSR 1521, Saurer 2, Haffner 10-FSR 1231, Juchert 12, and Pismis 3. We examined density maps, proper motion diagrams, and photometry to derive physical parameters. Results. We identified star clusters via overdensities in 2MASS, WISE, and DECaPS, confirmed with VVVX and Gaussian Kernel Density Estimation. Using Gaia proper motions, we refined memberships, building a high-likelihood cluster catalog. We derived extinction ($A_{Ks} = 0.07$-$0.50$), color excess ($E(J-Ks) = 0.16$-$0.60$), distances ($D = 2.06$-$8.64$ kpc), and Galactocentric distances ($R_G = 7.69$-$14.81$ kpc). Ages range from 20 Myr to 5 Gyr, metallicity from [Fe/H] = -0.5 to 0.5. Structural parameters include core radii ($r_c = 0.71'$-$5.21'$) and tidal radii ($r_t = 3.4'$-$12.0'$). Conclusions. We confirm the open cluster nature of nine targets, updating their physical parameters.

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arXiv2024

Three New Galactic Globular Cluster Candidates: FSR1700, Teutsch67, and CWNU4193

The VISTA Variables in the Via Láctea Extended Survey (VVVX) enables exploration of previously uncharted territories within the inner Milky Way (MW), particularly those obscured by stellar crowding and intense extinction. Our objective is to identify and investigate new star clusters to elucidate their intrinsic characteristics. Specifically, we are focused on uncovering new candidate Globular Clusters (GCs) situated at low Galactic latitudes, with the ultimate goal of completing the census of the MW GC system. Leveraging a combination of Near-InfraRed (NIR) data from the VVVX survey and Two Micron All Sky Survey (2MASS), along with optical photometry and precise proper motions (PMs) from the Gaia Data Release 3 (DR3), we are conducting a systematic characterisation of new GCs. As a result, we report the discovery and characterisation of four new Galactic clusters named FSR 1700, FSR 1415, CWNU 4193, and Teutsch 67, all located within the MW disk. We estimate a wide range of reddening, with values ranging from 0.44 to 0.73 mag for E(J-Ks). The heliocentric distances span from 10.3 to 13.2 kpc. Additionally, we determine their metallicities and ages, finding a range of -0.85 to -0.75 dex for [Fe/H] and ages approximately close to 11 Gyr, respectively. FSR 1415 is an exception, it is an old open cluster with age = 3 Gyr and [Fe/H] = -0.10. Furthermore, we fitted the radial density profiles to derive their structural parameters like tidal radius, core radius, and concentration parameters. In conclusion, based on their positions, kinematics, metallicities, and ages, and comparing our findings with existing literature, we categorise FSR 1700, Teutsch 67 and CWNU 4193 as genuine GC candidates, while FSR 1415 is an old open cluster exhibiting characteristics of a post core-collapse cluster.

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arXiv2023

The VISCACHA survey -- IX. The SMC Southern Bridge in 8D

The structure of the Small Magellanic Cloud (SMC) outside of its main body is characterised by tidal branches resulting from its interactions mainly with the Large Magellanic Cloud (LMC). Characterising the stellar populations in these tidal components helps to understand the dynamical history of this galaxy and of the Magellanic system in general. We provide full phase-space vector information for Southern Bridge clusters. We performed a photometric and spectroscopic analysis of twelve SMC clusters, doubling the number of SMC clusters with full phase-space vector information known to date. We reclassify the sample considering 3D distances and 3D velocities. We found that some of the clusters classified as Southern Bridge objects according to the projected 2D classification actually belong to the Main Body and Counter-Bridge in the background. The comparison of the kinematics of the genuine foreground Bridge clusters with those previously analysed in the same way reveals that Southern Bridge clusters are moving towards the LMC and share the kinematics of the Northern Bridge. Adding to our sample clusters from the literature with CaT metallicity determinations we compare the age-metallicity relation of the Southern Bridge with the one of the Northern Bridge. We reinforce the idea that both regions do not seem to have experienced the same chemical enrichment history and that there is a clear absence of clusters in the Northern Bridge older than 3Gyr and more metal-poor than -1.1, which would not seem to be due to a selection effect.

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arXiv2023

The VISCACHA survey -- VIII. Chemical evolution history of Small Magellanic Cloud West Halo cluster

The chemical evolution history of the Small Magellanic Cloud (SMC) has been a matter of debate for decades. The challenges in understanding the SMC chemical evolution are related to a very slow star formation rate (SFR) combined with bursts triggered by the multiple interactions between the SMC and the Large Magellanic Cloud, a significant (~0.5 dex) metallicity dispersion for the SMC cluster population younger than about 7.5 Gyr, and multiple chemical evolution models tracing very different paths through the observed age-metallicity relation of the SMC. There is no doubt that these processes were complex. Therefore, a step-by-step strategy is required in order to better understand the SMC chemical evolution. We adopted an existing framework to split the SMC into regions on the sky, and we focus on the west halo in this work, which contains the oldest and most metal-poor stellar populations and is moving away from the SMC, that is, in an opposite motion with respect to the Magellanic Bridge. We present a sample containing ~60% of all west halo clusters to represent the region well, and we identify a clear age-metallicity relation with a tight dispersion that exhibits a 0.5 dex metallicity dip about 6 Gyr ago. We ran chemical evolution models and discuss possible scenarios to explain this metallicity dip, the most likely being a major merger accelerating the SFR after the event. This merger should be combined with inefficient internal gas mixing within the SMC and different SFRs in different SMC regions because the same metallicity dip is not seen in the AMR of the SMC combining clusters from all regions. We try to explain the scenario to better understand the SMC chemo-dynamical history.

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arXiv2023

The VISCACHA survey -- VII. Assembly history of the Magellanic Bridge and SMC Wing from star clusters

The formation scenario of the Magellanic Bridge during an encounter between the Large and Small Magellanic Clouds $\sim200\,$Myr ago, as proposed by $N$-body models, would be imprinted in the chemical enrichment and kinematics of its stars, and sites of ongoing star formation along its extension. We present an analysis of 33 Bridge star clusters using photometry obtained with the SOAR 4-m telescope equipped with adaptive optics for the VISCACHA survey. We performed a membership selection and derived self-consistent ages, metallicities, distances and reddening values via statistical isochrone fitting, as well as tidal radii and integrated masses from structure analysis. Two groups are clearly detected: 13 well-studied clusters older than the Bridge, with $0.5-6.8\,$Gyr and $\rm{[Fe/H]}<-0.6\,$dex; and 15 clusters with $< 200\,$Myr and $\rm{[Fe/H]}>-0.5\,$dex, probably formed in-situ. The old clusters follow the overall age and metallicity gradients of the SMC, whereas the younger ones are uniformly distributed along the Bridge. The main results are as follows: $(i)$ we derive ages and metallicities for the first time for 9 and 18 clusters, respectively; $(ii)$ we detect two metallicity dips in the age-metallicity relation of the Bridge at $\sim 200\,$Myr and $1.5\,$Gyr ago for the first time, possibly chemical signatures of the formation of the Bridge and Magellanic Stream; $(iii)$ we estimate a minimum stellar mass for the Bridge of $3-5 \times 10^5\,M_\odot$; $(iv)$ we confirm that all the young Bridge clusters at $\rm{RA} < 3^h$ are metal-rich $\rm{[Fe/H]} \sim -0.4\,$dex.

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arXiv2022

The VISCACHA survey -- VI. Dimensional study of the structure of 82 star clusters in the Magellanic Clouds

We present a study of the internal structure of 82 star clusters located at the outer regions of the Large Magellanic Cloud and the Small Magellanic Cloud using data of the VISCACHA Survey. Through the construction of the minimum spanning tree, which analyzes the relative position of stars within a given cluster, it was possible to characterize the internal structure and explore the fractal or subclustered distribution for each cluster. We computed the parameters m (which is the average length of the connected segments normalized by the area), s (which is the mean points separation in units of cluster radius), and Q (the ratio of these components). These parameters are useful to distinguish between radial, homogeneous, and substructured distributions of stars. The dependence of these parameters with the different characteristics of the clusters, such as their ages and spatial distribution, was also studied. We found that most of the studied clusters present a homogeneous stellar distribution or a distribution with a radial concentration. Our results are consistent with the models, suggesting that more dynamically evolved clusters seem to have larger Q values, confirming previous results from numerical simulations. There also seems to be a correlation between the internal structure of the clusters and their galactocentric distances, in the sense that for both galaxies, the more distant clusters have larger Q values. We also paid particular attention to the effects of contamination by non-member field stars and its consequences finding that field star decontamination is crucial for these kinds of studies.

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arXiv2022

Ca Triplet Metallicities and Velocities for twelve Globular Clusters towards the Galactic Bulge

Globular clusters (GCs) are excellent tracers of the formation and early evolution of the Milky Way. The bulge GCs (BGCs) are particularly important because they can reveal vital information about the oldest, in-situ component of the Milky Way. We aim at deriving mean metallicities and radial velocities for 13 GCs that lie towards the bulge and are generally associated with this component. We use near infrared low resolution spectroscopy with the FORS2 instrument on the VLT to measure the wavelengths and equivalent widths of the CaII triplet (CaT) lines for a number of stars per cluster. We derive radial velocities, ascertain membership and apply known calibrations to determine metallicities for cluster members, for a mean of 11 members per cluster. We derive mean cluster RV values to 3 km/s, and mean metallicities to 0.05 dex. Our sample has metallicities lying between -0.21 and -1.64 and is distributed between the traditional metal-rich BGC peak near [Fe/H] aprox. -0.5 and a more metal-poor peak around [Fe/H] aprox. -1.1, which has recently been identified. These latter are candidates for the oldest GCs in the Galaxy, if blue horizontal branches are present, and include BH 261, NGC 6401, NGC 6540, NGC 6642, and Terzan 9. Finally, Terzan 10 is even more metal-poor. However, dynamically, Terzan 10 is likely an intruder from the halo, possibly associated with the Gaia-Enceladus or Kraken accretion events. Terzan 10 is also confirmed as an Oosterhotype II GC based on our results. The lone halo intruder in our sample, Terzan 10, is conspicuous for also having by far the lowest metallicity, and casts doubt on the possibility of any bonafide BGCs at metallicities below about aprox. -1.5.

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arXiv2022

The VISCACHA survey -- V. Rejuvenating three faint SMC clusters

We present the analysis of three faint clusters of the Small Magellanic Cloud RZ82, HW42 and RZ158. We employed the SOAR telescope instrument SAM with adaptive optics, allowing us to reach to V~23-24 mag, unprecedentedly, a depth sufficient to measure ages of up to about 10-12Gyr. All three clusters are resolved to their centres, and the resulting colour-magnitude diagrams (CMDs) allow us to derive ages of 3.9, 2.6, and 4.8Gyr respectively. These results are significantly younger than previous determinations (7.1, 5.0, and 8.3Gyr, respectively), based on integrated photometry or shallower CMDs. We rule out older ages for these clusters based on deep photometry and statistical isochrone fitting. We also estimate metallicities for the three clusters of [Fe/H]=-0.68, -0.57 and -0.90, respectively. These updated ages and metallicities are in good agreement with the age-metallicity relation for the bulk of SMC clusters. Total cluster masses ranging from ~7-11x10^3Mo were estimated from integrated flux, consistent with masses estimated for other SMC clusters of similar ages. These results reduce the number of SMC clusters known to be older than about 5 Gyr and highlight the need of deep and spatially resolved photometry to determine accurate ages for older, low-luminosity SMC star clusters.

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arXiv2022

Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. VI. Analysis of chemical properties of the Main Body

We derived radial velocities and CaT metallicity of more than 150 red giants stars in six SMC star clusters and their surrounding fields, with the instrument GMOS on GEMINI-S. The mean cluster radial velocity and metallicity were obtained with mean errors of 2.2 km\,s$^{-1}$ and 0.03 dex, while the mean field metallicities have a mean error of 0.13 dex. We add this information to that available for another 51 clusters and 30 fields with CaT metallicities on the same scale. Using this expanded sample we analize the chemical properties of the SMC Main Body, defined as the inner 3.4 degrees in semimajor axis. We found a high probability that the metallicity distribution of the Main Body clusters is bimodal with a metal-rich and a metal-poor cluster group, having mean metallicities with a dispersion of $μ= -0.80$, $σ= 0.06$ and $μ= -1.15$, $σ= 0.10$ dex, respectively. On the other hand, Main Body field stars show a unimodal metallicity distribution peaking at $[Fe/H] \sim -1$ and dispersion of $0.3$. Neither metal-rich nor metal-poor clusters present a metallicity gradient. However the full Main Body cluster sample and field stars have a negative metallicity gradient consistent with each other, but the one corresponding to clusters has a large error due to the large metallicity dispersion present in the clusters studied in that region. Metal-rich clusters present a clear age-metallicity relation, while metal-poor clusters present no chemical enrichment throughout the life of the galaxy. We present observational evidence that the chemical enrichment is complex in the SMC Main Body. Two cluster groups with potential different origins could be coexisting in the Main Body. More data with precise and homogeneous metallicities and distances are needed and dynamical simulations are required to understand possible different origins for the two possible cluster groups.

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arXiv2022

Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. V. Abundances and Velocities for 12 Massive Clusters

We aim to analyze the chemical evolution of the Small Magellanic Cloud adding 12 additional clusters to our existing sample having accurate and homogeneously derived metallicities. We are particularly interested in seeing if there is any correlation between age and metallicity for the different structural components to which the clusters belong. Spectroscopic metallicities of red giant stars are derived from the measurement of the equivalent width of the near-IR calcium triplet lines. Cluster membership analysis was carried out using criteria that include radial velocities, metallicities, proper motions and distance from the cluster center. The mean cluster radial velocity and metallicity were determined with a typical error of 2.1 km/s and 0.03 dex, respectively. We added this information to that available in the literature for other clusters studied with the same method, compiling a final sample of 48 clusters with metallicities homogeneously determined. Clusters of the final sample are distributed in an area of ~ 70 deg^2 and cover an age range from 0.4 Gyr to 10.5 Gyr. The metallicity distribution of our new cluster sample shows a lower probability of being bimodal than suggested in previous studies. The separate chemical analysis of clusters in the six components (Main Body, Counter-Bridge, West Halo, Wing/Bridge, Northern Bridge and Southern Bridge) shows that only clusters belonging to the Northern Bridge appear to trace a V-Shape, showing a clear inversion of the metallicity gradient in the outer regions. There is a suggestion of a metallicity gradient in the West Halo, similar to that previously found for field stars. It presents, however, a very large uncertainty. Also, clusters belonging to the West Halo, Wing/Bridge and Southern Bridge exhibit a well-defined age-metallicity relation with relatively little scatter in abundance at fixed age compared to other regions.

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arXiv2022

The VISCACHA survey -- IV. The SMC West Halo in 8D

The structure of the Small Magellanic Cloud (SMC) is very complex, in particular in the periphery that suffers more from the interactions with the Large Magellanic Cloud (LMC). A wealth of observational evidence has been accumulated revealing tidal tails and bridges made up of gas, stars and star clusters. Nevertheless, a full picture of the SMC outskirts is only recently starting to emerge with a 6D phase-space map plus age and metallicity using star clusters as tracers. In this work, we continue our analysis of another outer region of the SMC, the so-called West Halo, and combined it with the previously analysed Northern Bridge. We use both structures to define the Bridge and Counter-bridge trailing and leading tidal tails. These two structures are moving away from each other, roughly in the SMC-LMC direction. The West Halo form a ring around the SMC inner regions that goes up to the background of the Northern Bridge shaping an extended layer of the Counter-bridge. Four old Bridge clusters were identified at distances larger than 8 kpc from the SMC centre moving towards the LMC, which is consistent with the SMC-LMC closest distance of 7.5 kpc when the Magellanic Bridge was formed about 150Myr ago; this shows that the Magellanic Bridge was not formed only by pulled gas, but it also removed older stars from the SMC during its formation. We also found age and metallicity radial gradients using projected distances on sky, which are vanished when we use the real 3D distances.

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arXiv2021

The VISCACHA survey -- III. Star clusters counterpart of the Magellanic Bridge and Counter-Bridge in 8D

Context. The interactions between the SMC and LMC created the Magellanic Bridge, a stream of gas and stars pulled out of the SMC towards the LMC about 150 Myr ago. The tidal counterpart of this structure, which should include a trailing arm, has been predicted by models but no compelling observational evidence has confirmed the Counter-Bridge so far. Aims. The main goal of this work is to find the stellar counterpart of the Magellanic Bridge and Counter-Bridge. We use star clusters in the SMC outskirts as they provide 6D phase-space vector, age and metallicity that help characterise the outskirts of the SMC. Methods. Distances, ages and photometric metallicities are derived from fitting isochrones to the colour-magnitude diagrams from the VISCACHA survey. Radial velocities and spectroscopic metallicities are derived from the spectroscopic follow-up using GMOS in the CaII triplet region. Results. Among the seven clusters analysed in this work, five belong to the Magellanic Bridge and one belongs to the Counter-Bridge and the other to the transition region. Conclusions. The existence of the tidal counterpart of the Magellanic Bridge is evidenced by star clusters. The stellar component of the Magellanic Bridge and Counter-Bridge are confirmed in the SMC outskirts. These results are an important constraint for models that seek to reconstruct the history of the orbit and interactions between LMC-SMC and constrain their future interaction including with the Milky Way.

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arXiv2020

Panchromatic calibration of Ca II triplet luminosity dependence

(ABRIDGED) Context. The line strength of the Ca II triplet (CaT) lines are a proxy to measure metallicity from individual stellar spectra of bright red giant stars. It is a mandatory step to remove the magnitude (proxy for gravity, temperature and luminosity) dependence from the equivalent width (EW) of the lines before converting them into metallicities. The working empirical procedure used for decades is to use the relative magnitude with respect to the horizontal branch level. Aims. The V filter is broadly adopted as the reference magnitude, although a few works have used different filters (I and Ks, for example). In this work we investigate the dependence of the CaT calibration using griz filters from the DECam and the GMOS, G from Gaia, BVI filters from the MCPS, YJKs filters from VIRCAM. We use as a reference FORS2 V filter used in the original analysis of the sample. Methods. Red giant stars from clusters with known metallicity and available CaT equivalent widths are used as reference. Public photometric catalogues are taken from SMASH DR2, VMC, Gaia, MCPS surveys plus VISCACHA-GMOS data, for a selection of Small Magellanic Cloud clusters. The slopes are fitted using two and three lines to be applicable to most of the metallicity scales. Results. The magnitude dependence of the CaT EWs is well described by a linear relation using any filter analysed in this work. The slope increases with wavelength of the filters. The zero point (a.k.a. reduced equivalent width), that is the metallicity indicator, remains the same. Conclusions. If the same line profile function is used with the same bandpasses and continuum regions, and the total EW comes from the same number of lines (2 or 3), then the reduced EW is the same regardless the filter used. Therefore, any filter can be used to convert the CaT equivalent widths into metallicity for a given CaT calibration.

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arXiv2020

Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud V: Multiple Populations in ancient Globular Clusters

We examine four ancient Large Magellanic Cloud (LMC) globular clusters (GCs) for evidence of multiple stellar populations using the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope Programme GO-14164. NGC 1466, NGC 1841, and NGC 2257 all show evidence for a redder, secondary population along the main-sequence. Reticulum does not show evidence for the presence of a redder population, but this GC has the least number of stars and Monte Carlo simulations indicate that the sample of main sequence stars is too small to robustly infer whether a redder population exists in this cluster. The second, redder, population of the other three clusters constitutes $\sim30-40\%$ of the total population along the main-sequence. This brings the total number of ancient LMC GCs with known split or broadened main-sequences to five. However, unlike for Hodge 11 and NGC 2210 (see arXiv:1904.01434), none of the clusters show evidence for multiple populations in the horizontal branch. We also do not find evidence of a second population along the Red Giant Branch (RGB).

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arXiv2019

Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud IV: Evidence for Multiple Populations in Hodge 11 and NGC 2210

We present a multiple population search in two old Large Magellanic Cloud (LMC) Globular Clusters, Hodge 11 and NGC 2210. This work uses data from the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope from programme GO-14164 in Cycle 23. Both of these clusters exhibit a broadened main sequence with the second population representing ($20 \pm \! \sim \! 5$)% for NGC 2210 and ($30 \pm \! \sim \! 5$)% for Hodge 11. In both clusters, the smaller population is redder than the primary population, suggesting CNO variations. Hodge 11 also displays a bluer second population in the horizontal branch, which is evidence for helium enhancement. However, even though NGC 2210 shows similarities to Hodge 11 in the main sequence, there does not appear to be a second population on NGC 2210's horizontal branch. This is the first photometric evidence that ancient LMC Globular Clusters exhibit multiple stellar populations.

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arXiv2015

Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. III. Abundances and Velocities for a Sample of 14 Clusters

We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters in the region of the CaII lines with FORS2 on the Very Large Telescope (VLT). We determined the mean metallicity and radial velocity with mean errors of 0.05 dex and 2.6 km/s, respectively, from a mean of 6.5 members per cluster. One cluster (B113) was too young for a reliable metallicity determination and was excluded from the sample. We combined the sample studied here with 15 clusters previously studied by us using the same technique, and with 7 clusters whose metallicities determined by other authors are on a scale similar to ours. This compilation of 36 clusters is the largest SMC cluster sample currently available with accurate and homogeneously determined metallicities. We found a high probability that the metallicity distribution is bimodal, with potential peaks at -1.1 and -0.8 dex. Our data show no strong evidence of a metallicity gradient in the SMC clusters, somewhat at odds with recent evidence from CaT spectra of a large sample of field stars Dobbie et al. (2014). This may be revealing possible differences in the chemical history of clusters and field stars. Our clusters show a significant dispersion of metallicities, whatever age is considered, which could be reflecting the lack of a unique AMR in this galaxy. None of the chemical evolution models currently available in the literature satisfactorily represents the global chemical enrichment processes of SMC clusters.

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