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Since recent years, mass segregation driven by two-body relaxation in star clusters has been proposed to be measured by the so-called dynamical clock, $A^+$, a measure of the area enclosed between the cumulative radial distribution of blue straggler stars and that of a reference population. Since star clusters spend their lifetime immersed in the gravitational potential of their host galaxy, they are also subject to the effects of galactic tides. In this work, I show that the $A^+$ index of a star cluster depends on both, its internal dynamics as it were in isolation and on the effects of galactic tides. Particularly, I focused on the largest sample of open clusters harboring blue straggler stars with robust cluster membership. I found that these open clusters exhibit an overall dispersion of the $A^+$ index in diagnostic diagrams where Milky Way globular clusters show a clear linear trend. However, as also experienced by globular clusters, $A^+$ values of open clusters show some dependence on their galactocentric distances, in the sense that clusters located closer or farther that $\sim$ 11 kpc from the Galactic center have larger and smaller $A^+$ values, respectively. This different response to two-body relaxation and galactic tides in globular and open clusters, which happen concurrently, can be due to their different masses. More massive clusters can somehow protect their innermost regions from galactic tides more effectively., Comment: 9 pages, 22 figures. Accepted for publication in J. Astrophysics & Astronomy

We present results of the analysis of a set of images obtained in the field of the Milky Way bulge globular cluster NGC 6355 using the Dark Energy Camera, which is attached to the 4m Blanco telescope of the Cerro-Tololo Interamerican Observatory. We dealt with a heavy differential absorption across the observed field, a crowded field star population, and the superposition of field stars on to the cluster color-magnitude diagram main features to produce an intrinsic cluster stars density map. The resulting stellar density map reveals the presence of an extended envelope, a tidal tail, and scattered debris; the tidal tails pointing toward the Milky Way center. Such extra-tidal overdensities, detected above the mean star field density, resulted to be between four and six times larger that the local star field density fluctuation. They have also been recently generated by two independent studies which performed numerical simulations of synthetic tidal tails of Milky Way globular clusters. These results contrast with previous theoretical speculations about the possibility to detect tidal tails of globular clusters with chaotic orbits because they would be washed out after they were generated., Comment: 9 pages, 8 figures. The Astronomical Journal, in press. arXiv admin note: text overlap with arXiv:2401.08791

The spatial metallicity distribution of star clusters in the Small Magellanic Cloud (SMC) has recently been found to correlate as a V-shaped function with the semi-major axis of an elliptical framework proposed to assume a projected galaxy flattening. We report results on the impact that the use of such a framework can produce on our understanding of the SMC formation and its chemical enrichment. We show that clusters with similar semi-major axes are placed at a very different distances from the SMC centre. The recently claimed bimodal metallicity distribution of clusters projected on the innermost SMC regions and the V-shaped metallicity gradient fade away when actual distances are used. Although a large dispersion prevails, clusters older than $\sim$ 1 Gyr exhibit a shallow metallicity gradient, caused by slightly different spatial distributions of clusters younger and older than $\sim$ 4 Gyr; the former being more centrally concentrated and having a mean metallicity ([Fe/H]) $\sim$ 0.15 dex more metal-rich than that of older clusters. This metallicity gradient does not show any dependence with the position angle, except for clusters placed beyond 11 kpc, which are located in the eastern side of the galaxy., Comment: 5 pages, 4 figures. Accepted for publication in MNRAS

The age distribution of the open cluster system is a key piece of information to decipher the star formation history of the Milky Way disk. Recently, a remarkable earlier drop of its older end was found, which caught our attention. Precisely, we analyzed in detail the population of open clusters older than 1 Gyr located inside a circle of 2.0 kpc from the Sun contained in the Milky Way Star Cluster catalog, using the Data Release 3.0 of the Gaia survey, and found that it contains a slightly larger old open cluster population with respect to that witnessing the earlier drop age distribution. However, there are still some aspects that deserve further attention in order to undoubtedly handle a statistically complete cluster sample, that allows us to comprehensively know the older end of the open cluster age distribution function. We discuss some reasons that affect such a completeness, among them, the photometric depth of the database employed, the performance of machine learning techniques used to recognize open clusters, the cleaning of cluster color-magnitude diagrams from field star contamination, etc., Comment: 13 pages, 11 figures. Accepted for publication in JApA

The tangential velocity dispersion of stars belonging to the Milky Way globular cluster's tidal tails has recently been found from N-body simulations to be a parameter that distinguishes between cored and cuspy profiles of low-mass dwarf galaxy dark matter subhaloes where that globular cluster formed, and the in-situ formation scenario. In this context, we discovered that M5's tidal tails are composed by stars at two different metallicity regimes ([Fe/H] ~ -1.4 dex and -2.0 dex). The more metal-rich tidal tail stars are of the same metal content than M5's members and have a tangential velocity dispersion that coincides with the predicted value for a cuspy formation scenario (subhalo mass $\sim$ 10$^9$ M$_{\odot}$). The more metal-poor stars, that are found along the entire M5 tidal tails and have similar distributions to their more metal-rich counterparts in the M5 colour-magnitude diagram and orbit trajectory, have a tangential velocity dispersion that refers to a cored subhalo (mass $\sim$ 10$^9$ M$_{\odot}$) or an in-situ formation scenario. In order to reconcile the dual distribution of M5 tidal tail stars, in kinematics and chemistry, we propose that M5 collided with another more metal-poor and less massive globular cluster anytime before or after it was accreted into the Milky Way., Comment: 4 pages, 1 figure. Accepted for publication in MNRAS Letters

The ancient Large Magellanic Cloud (LMC) globular cluster NGC 2005 has recently been reported to have an ex-situ origin, thus, setting precedents that the LMC could have partially formed from smaller merged dwarf galaxies. We here provide additional arguments from which we conclude that is also fairly plausible an in-situ origin of NGC 2005, based on the abundance spread of a variety of chemical elements measured in dwarf galaxies, their minimum mass in order to form globular clusters, the globular cluster formation imprints kept in their kinematics, and the recent modeling showing that explosions of supernovae are responsible for the observed chemical abundance spread in dwarf galaxies. The present analysis points to the need for further development of numerical simulations and observational indices that can help us to differentiate between two mechanisms of galaxy formation for the LMC, namely, a primordial dwarf or an initial merging event of smaller dwarfs., Comment: 11 pages, 2 figures. Accepted for publication in The Astronomical Journal

Theoretical models have suggested peculiar velocity dispersion profiles of star clusters facing dissolution. They predicted that, besides bound stars that still belong to the star cluster, and unbound ones already stripped off, there is an intermediate population of stars that having acquired the enough energy to escape the cluster are still within the cluster Jacobi radius. Both, potential escapers and unbound stars, show hot kinematics, not observed along tidal tails of star clusters. We report on the first evidence of an open cluster with stars crossing such a transitional scenario, namely: ASCC 92. The open cluster gathers nearly 10 percent of its initial total mass, and is moving toward Galactic regions affected by higher interstellar absorption. Precisely, the obscured appearance of the cluster could have hampered disentangling its true internal dynamical evolutionary stage, previously., Comment: 8 pages, 5 figures. Accepted for publication in MNRAS

I revisited the age of the Small Magellanic Cloud cluster HW 42, whose previous estimates differ in more than 6 Gyr, thus challenging the most updated knowledge of the SMC star formation history. I performed an analysis of number stellar density profiles at different brightness levels; carried out a field star decontamination of the cluster color-magnitude diagram; and estimated the cluster fundamental parameters from the minimization of likelihood functions and their uncertainties from standard bootstrap methods. I conclude that HW 42 is a 6.2$^{\rm +1.6}_{\rm -1.3}$ Gyr old ([Fe/H] = -0.89$^{\rm +0.10}_{\rm -0.11}$ dex) SMC cluster projected on to a SMC composite star field population which shows variations in magnitude, color, and stellar density of Main Sequence stars. The present outcome solves the conundrum of the previous age discrepancies and moves HW~42 to a region in the SMC age-metallicity relationship populated by star clusters., Comment: 3 pages, 1 figure. Accepted for publication in Research Notes of the AAS

We report results on the analysis of eleven new Milky Way open cluster candidates, recently discovered from the detection of stellar overdensities in the Vector Point diagram, by employing extreme deconvolution Gaussian mixture models. We treated these objects as real open clusters and derived their fundamental properties with their associated intrinsic dispersions by exploring the parameter space through the minimization of likelihood functions on generated synthetic colour-magnitude diagrams (CMDs). The intrinsic dispersions of the resulting ages turned out to be much larger than those usually obtained for open clusters. Indeed, they resemble those of ages and metallicities of composite star field populations. We also traced their stellar number density profiles and mass functions, derived their total masses, Jacobi and tidal radii, which helped us as criteria while assessing their physical nature as real open clusters. Because the eleven candidates show a clear gathering of stars in the proper motion plane and some hint for similar distances, we concluded that they are possibly sparse groups of stars., Comment: 9 pages, 6 figures. Accepted for publication in MNRAS

We study 147 star clusters in the Large Magellanic Cloud (LMC) in order to determine their mean metallicities and ages, as well as the mean metallicities of 80 surrounding fields. We construct an age-metallicity relation (AMR) for the clusters in the LMC. For this purpose, we used Str\"omgren photometry obtained with the SOI camera on the 4.1 m SOAR telescope. We found the mean metallicity and age for 110 star clusters. For the remaining 37, we provide an age estimation only. To the best of our knowledge, for 29 clusters from our sample, we provide both the metallicity and age for the first time, whereas for 66 clusters, we provide a first determination of the metallicity, and for 43 clusters, the first estimation of the age. We also calculated the mean metallicities for stars from 80 fields around the clusters. The old, metal-poor star clusters occur both in and out of the LMC bar region, while intermediate-age clusters are located mostly outside of the bar. The majority of star clusters younger than 1 Gyr are located in the bar region. We find a good agreement between our AMR and theoretical models of the LMC chemical enrichment, as well as with AMRs for clusters from the literature. Next, we took advantage of 26 stellar clusters from our sample which host Cepheid variables and used them as an independent check of the correctness of our age determination procedure. We used period-age relations for Cepheids to calculate the mean age of a given cluster and compared it with the age obtained from isochrone fitting. We find good agreement between these ages, especially for models taking into account additional physical processes (e.g., rotation). We also compared the AMR of the LMC and Small Magellanic Cloud (SMC) derived in a uniform way and we note that they indicate possible former interaction between these two galaxies., Comment: 40 pages, 17 figures, 6 tables, Published in A&A; The 8th (last) column in Table A.1 has been corrected compared to the published version

We present results on the recently discovered stellar system YMCA-1, for which physical nature and belonging to any of the Magellanic System galaxies have been irresolutely analyzed. We used SMASH and {\it Gaia} EDR3 data sets to conclude that we are dealing with a small star cluster. Its reddening free, field star decontaminated colour-magnitude diagram was explored in order to obtain the cluster parameters. We found that YMCA-1 is a small (435 M$_{\odot}$), moderately old (age = 9.6 Gyr), moderately metal-poor ([Fe/H] = -1.16 dex) star cluster, located at a nearly Small Magellanic Cloud (SMC) distance (60.9 kpc) from the Sun, at $\sim$ 17.1 kpc to the East from the Large Magellanic Cloud (LMC) centre. The derived cluster brightness and size would seem to suggest some resemblance to the recently discovered faint star clusters in the Milky Way (MW) outer halo, although it does not match their age-metallicty relationship, nor those of MW globular clusters formed in-situ or ex-situ, nor that of LMC clusters either, but is in agreement with that of SMC old star clusters. We performed numerical Monte Carlo simulations integrating its orbital motion backward in the MW-LMC-SMC system with radially extended dark matter haloes that experience dynamical friction, and by exploring different radial velocity (RV) regimes for YMCA-1. For RVs $\gtrsim$ 300 km/s, the cluster remains bound to the LMC during the last 500 Myrs. The detailed tracked kinematic of YMCA-1 suggests that its could have been stripped by the LMC from the SMC during any of the close interactions between both galaxies, a scenario previously predicted by numerical simulations., Comment: 9 pages, 6 figures. Accepted for publication in MNRAS

We study the outer regions of the Milky Way globular cluster NGC 7089 based on new Dark Energy Camera (DECam) observations. The resulting background cleaned stellar density profile reveals the existence of an extended envelope. We confirm previous results that cluster stars are found out to ~ 1deg from the cluster's centre, which is nearly three times the value of the most robust tidal radii estimations. We also used results from direct N-body simulations in order to compare with the observations. We found a fairly good agreement between the observed and numerically generated stellar density profiles. Because of the existence of gaps and substructures along globular cluster tidal tails, we closely examined the structure of the outer cluster region beyond the Jacobi radius. We extended the analysis to a sample of 35 globular clusters, 20 of them with observed tidal tails. We found that if the stellar density profile follows a power law ~ r**(-alpha), the alpha slope correlates with the globular cluster present mass, in the sense that, the more massive the globular cluster the smaller the alpha value. This trend is not found in globular clusters without observed tidal tails. The origin of such a phenomenon could be related, among other reasons, to the proposed so-called potential escapers or to the formation of globular clusters within dark matter mini-haloes., Comment: 9 pages, 4 figures. Accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:2111.02496

We confirm the existence of a second Large Magellanic Cloud (LMC) star cluster, KMHK 1592, with an age that falls in the middle of the so-called LMC star cluster age gap, a long period of time (~ 4 - 11 Gyr) where no star cluster had been uncovered, except ESO121-SC03. The age (8.0+-0.5 Gyr) and the metallicity ([Fe/H]=-1.0+-0.2 dex) of KMHK1592 were derived from the fit of theoretical isochrones to the intrinsic star cluster colour-magnitude diagram sequences, which were unveiled using a robust star-by-star membership probability procedure. Because of the relative low brightness of the star cluster, deep GEMINI GMOS images were used. We discuss the pros and cons of three glimpsed scenarios that could explain the presence of both LMC age gap star clusters in the outskirts of the LMC, namely: in-situ star cluster formation, capture from the Small Magellanic Cloud, or accretion of a small dwarf galaxy., Comment: 5 pages, 4 figures. Accepted for publication in MNRAS Letters

We report the first evidence of an on-going collision between two star clusters in our Galaxy, namely IC 4665 and Collinder 350. These are open clusters located at a distance of ~330 pc from the Sun and ~100 pc above the Galactic plane, and they both have prograde motions with only a small difference in their velocities (Collinder 350 moves ~5 km/s faster than IC 4665); as inferred from ESA/Gaia based catalogue. Interestingly, the two clusters are physically separated by only 36 pc in space; a distance that is smaller than the sum of their respective radii. Furthermore, the clusters exhibit signatures of elongated stellar density distributions, and we also detect an onset of an inter-cluster stellar bridge. Moreover, the orbit analysis suggests that the younger cluster IC 4665 (age=53 Myr) must have formed at a distance > 500 pc away from Collinder 350 (age=617 Myr). These findings together imply that the two clusters do not represent merging of two objects in a binary system, rather, what we are witnessing is an actual collision between two independently formed star clusters. This collision phenomenon provides a unique opportunity to explore new aspects of formation and evolution theory of star clusters., Comment: 8 pages, 9 figures. Accepted for publication in MNRAS Letters

Globular clusters are prone to lose stars while moving around the Milky Way. These stars escape the clusters and are distributed throughout extended envelopes or tidal tails. However, such extra-tidal structures are not observed in all globular clusters, and yet there is no structural or dynamical parameters that can predict their presence or absence. NGC\,6864 is an outer halo globular cluster with reported no observed tidal tails. We used Dark Energy Camera (DECam) photometry reaching $\sim$ 4 mag underneath its main sequence turnoff to confidently detect an extra-tidal envelope, and stellar debris spread across the cluster outskirts. These features emerged once robust field star filtering techniques were applied to the fainter end of the observed cluster main sequence. NGC\,6864 is associated to the {\it Gaia}-Enceladus dwarf galaxy, among others 28 globular clusters. Up-to-date, nearly 64$\%$ of them have been targeted looking for tidal tails and most of them have been confirmed to exhibit tidal tails. Thus, the present outcomes allow us to speculate on the possibility that {\it Gaia}-Enceladus globular clusters share a common pattern of mass loss by tidal disruption., Comment: 9 pages, 7 figures. Accepted for publication in MNRAS

The outer northeastern region of the Small Magellanic Cloud (SMC) is populated by a shell-like overdensity whose nature was recently investigated. We analyzed twenty catalogued star clusters projected onto it from Survey of the MAgellanic Stellar History data sets. After carrying out a cleaning of field stars in the star cluster colour-magnitude diagrams (CMDs), and deriving their astrophysical properties from the comparison between the observed and synthetic CMDs, we found that four objects are not genuine star clusters, while the remaining ones are young star clusters (11, age $\sim$ 30-200 Myr) and intermediate-age (5, age $\sim$ 1.7-2.8 Gyr) star clusters, respectively. The resulting distances show that intermediate-age and some young star clusters belong to the SMC main body, while the remaining young star clusters are nearly 13.0 kpc far away from those in the SMC, revealing that the shell-like overdensity is more extended along the line-of-sight than previously thought. We also found a clear age trend and a blurred metallicity correlation along the line-of-sight of young clusters, in the sense that the farther a star cluster from the SMC, the younger, the more metal rich, and the less massive it is. These young clusters are also affected by a slightly larger interstellar reddening than the older ones in the shell-like overdensity. These outcomes suggest that the shell-like overdensity can possibly be another tidally perturbed/formed SMC stellar structure from gas striped off its body, caused by the interaction with the Large Magellanic Cloud or the Milky Way., Comment: 10 pages, 7 figures. Accepted for publication in MNRAS

We analyzed the largest Small Magellanic Cloud (SMC) cluster sample (32) with proper motions and radial velocity measurements, from which we obtained their space velocity components. By adopting as a reference the recent best-fitted rotating disc of SMC star clusters as a function of the position angle, we computed their residual velocity vectors, and compared their magnitudes ($\Delta$V) with that of a cluster with residual velocity components equal to the velocity dispersions along the three independent SMC rotating disc axes of motion ($\Delta$V = 60 km/s). We found that clusters that belong to SMC tidally induced structures have $\Delta$V > 50 km/s, which suggests that space velocities of clusters in the process of escaping the rotating disc kinematics, are measurably different. Studied clusters pertaining to a northern branch of the Magellanic Bridge, the main Magellanic Bridge, the Counter-Bridge and the West halo give support to these findings. NGC 121, the oldest known SMC cluster, does not belong to any SMC tidal feature, and has $\Delta$V = 64 km/s, slightly above the boundary between bound and kinematically perturbed clusters., Comment: 7 pages, 4 figures. Accepted for publication in MNRAS

Recently, new Sagittarius (Sgr) dwarf galaxy globular clusters were discovered, which opens the question on the actual size of the Sgr globular cluster population, and therefore on our understanding of the Sgr galaxy formation and accretion history onto the Milky Way. Based on Gaia EDR3 and SDSS IV DR16 (APOGEE-2) data sets, we performed an analysis of the color-magnitude diagrams (CMDs) of the eight new Sgr globular clusters found by from a sound cleaning of the contamination of Milky Way and Sgr field stars, complemented by Minniti et al. (2021b) available kinematic and metal abundance information. The cleaned CMDs and spatial stellar distributions reveal the presence of stars with a wide range of cluster membership probabilities. Minni 332 turned out to be a younger (< 9 Gyr) and more metal-rich ([M/H] > -1.0 dex) globular cluster than M54, the nuclear Sgr globular cluster, as could also be the case of Minni 342, 348, and 349, although their results are less convincing. Minni 341 could be an open cluster candidate (age < 1 Gyr, [M/H] ~ -0.3 dex), while the analyses of Minni 335, 343, and 344 did not allow us to confirm their physical reality. We also built the Sgr cluster frequency (CF) using available ages of the Sgr globular clusters and compared it with that obtained from the Sgr star formation history. Both CFs are in excellent agreement. However, the addition of eight new globular clusters with ages and metallicities distributed according to the Sgr age-metallicity relationship turns out in a remarkably different CF., Comment: 13 pages, 7 figures. Accepted for publication in The Astronomical Journal

We study the outer regions of the Milky Way globular cluster NGC6809 based on Dark Energy Camera (DECam) observations, which reach nearly 6 mag below the cluster main sequence (MS) turnoff. In order to unveil its fainter outermost structure, we built stellar density maps using cluster MS stars, once the contamination of field stars was removed from the cluster color-magnitude diagram. We found that only the resulting stellar density map for the lightest stars exhibits some excesses of stars at opposite sides from the cluster centre that diminish soon thereafter at ~ 0.32 deg. Studied globular clusters with apogalactic distances smaller than that of NGC6809 (5.5 kpc) do not have observed tidal tails. The lack of detection of tidal tails in the studied inner globular cluster sample could be due to the reduced diffusion time of tidal tails by the kinematically chaotic nature of the orbits of these globular clusters, thus shortening the time interval during which the tidal tails can be detected. Further investigations with an enlarged cluster sample are needed to confirm whether chaotic and non-chaotic orbits are responsible for the existence of globular clusters with tidal tails and those with extra-tidal features that are different from tidal tails or without any signatures of extended stellar density profiles., Comment: 9 pages, 4 figures. Accepted for publication in MNRAS

We report results of proper motions of 25 known Small Magellanic Cloud (SMC) clusters (ages ~ 1 - 10 Gyr old) derived from Gaia EDR3 data sets. When these mean proper motions are gathered with existent radial velocity measurements to compose the clusters' velocity vectors, we found the parameter values of a rotation disk that best resemble their observed motions, namely: central coordinates and distance, inclination and position angle of the line-of-node, proper motion in right ascension and declination and systemic velocity, rotation velocity and velocity dispersion. The SMC cluster rotation disk seems to be at some level kinematically synchronized with the rotation of field red giants recently modeled using DR2 data sets. Such a rotation disk is seen in the sky as a tilted edge-on disk, with a velocity dispersion perpendicular to it twice as big as that in the plane of the disk. Because the direction perpendicular to the disk is nearly aligned with the Magellanic Bridge, we interpret the larger velocity dispersion as a consequence of the SMC velocity stretching caused by the tidal interaction with the Large Magellanic Cloud. Rotation alone would not seem sufficient to explain the observed kinematic behaviors in the SMC., Comment: 5 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics

Recently, a noticeable number of new star clusters was identified in the outskirts of the Large Magellanic Cloud (LMC) populating the so-called star cluster age gap, a space of time (~ 4-12 Gyr) where the only known star cluster is up-to-date ESO121-SC\,03. We used Survey of the Magellanic Stellar History (SMASH) DR2 data sets, as well as those employed to identify these star cluster candidates, to produce relatively deep color-magnitude diagrams (CMDs) of 17 out of 20 discovered age gap star clusters with the aim of investigating them in detail. Our analysis relies on a thorough CMD cleaning procedure of the field star contamination, which presents variations in its stellar density and astrophysical properties, such as luminosity and effective temperature, around the star cluster fields. We built star cluster CMDs from stars with membership probabilities assigned from the cleaning procedure. These CMDs and their respective spatial distribution maps favor the existence of LMC star field density fluctuations rather than age gap star clusters, although a definitive assessment on them will be possible from further deeper photometry., Comment: 9 pages, 10 figures. Accepted for publication in The Astronomical Journal

The central (`bulge') region of the Milky Way is teeming with a significant fraction of mildly metal-deficient stars with atmospheres that are strongly enriched in cyanogen ($^{12}$C$^{14}$N). Some of these objects, which are also known as nitrogen-enhanced stars, are hypothesised to be relics of the ancient assembly history of the Milky Way. Although the chemical similarity of nitrogen-enhanced stars to the unique chemical patterns observed in globular clusters has been observed, a direct connection between field stars and globular clusters has not yet been proven. In this work, we report on high-resolution, near-infrared spectroscopic observations of the bulge globular cluster NGC 6723, and the serendipitous discovery of a star, 2M18594405$-$3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio ([N/Fe]$\gtrsim + 0.94$) is well above the typical Galactic field-star levels, and it exhibits noticeable enrichment in the heavy $s$-process elements (Ce, Nd, and Yb), along with moderate carbon enrichment; all characteristics are known examples in globular clusters. This result suggests that some of the nitrogen-enhanced stars in the bulge likely originated from the tidal disruption of globular clusters., Comment: Astronomy & Astrophysics, in press. 16 pages, 8 figures, 2 tables

In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. We used Str\"omgren photometry obtained with the 4.1 m SOAR telescope and take advantage of $(b - y)$ and $m1$ colors for which there is a metallicity calibration presented in the literature. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Str\"omgren photometry. We confirm earlier observations that younger, more metal-rich star clusters are concentrated in the central regions of the galaxy, while older, more metal-poor clusters are located farther from the SMC center. We construct the age-metallicity relation for the studied clusters and find good agreement with theoretical models of chemical enrichment, and with other literature age and metallicity values for those clusters. We also provide the mean metallicities for old and young populations of the field stars surrounding the clusters, and find the latter to be in good agreement with recent studies of the SMC Cepheid population. Finally, the Str\"omgren photometry obtained for this study is made publicly available., Comment: 22 pages, 12 figures, 6 tables, Published in A&A

It has been recently shown from observational data sets the variation of structural parameters and internal dynamical evolution of star clusters in the Milky Way and in the Large Magellanic Cloud (LMC), caused by the different gravitational field strengths that they experience. We report here some hints for such a differential tidal effects in structural parameters of star clusters in the Small Magellanic Cloud (SMC), which is nearly 10 times less massive than the LMC. A key contribution to this study is the consideration of the SMC as a triaxial spheroid, from which we estimate the deprojected distances to the SMC center of the statistically significant sample of star clusters analyzed. By adopting a 3D geometry of the SMC, we avoid the spurious effects caused by considering that a star cluster observed along the line-of-sight is close to the galaxy center. When inspecting the relationships between the star cluster sizes (represented by the 90% light radii), their eccentricities, masses and ages with the deprojected distances, we find: (i) the star cluster sizes are not visibly affected by tidal effects, because relatively small and large objects are spread through the SMC body. (ii) Star clusters with large eccentricities (> 0.4) are preferentially found located at deprojected distances smaller than $\sim$ 7-8 kpc, although many star clusters with smaller eccentricities are also found occupying a similar volume. (iii) Star clusters more massive than log(M /Mo) $\sim$ 4.0 are among the oldest star clusters, generally placed in the outermost SMC region and with a relative small level of flattening. These findings contrast with the more elongated, generally younger, less massive and innermost star clusters., Comment: 6 pages, 6 figures. Accepted por publication in Astronomy & Astrophysics

We study the outer regions of the Milky Way globular cluster NGC6981 from publicly available $BV$ photometry and new Dark Energy Camera (DECam) observations, both reaching nearly 4 mag below the cluster main sequence (MS) turnoff. While the $BV$ data sets reveal the present of extra-tidal features around the cluster, the much larger field of view of DECam observations allowed us to identify some other tidal features, which extend from the cluster toward the opposite direction to the Milky Way center. These cluster structural features arise from stellar density maps built using MS stars, once the cluster color-magnitude diagram was cleaned from the contamination of field stars. We also performed $N$-body simulations in order to help us to understand the spatial distribution of the extra-tidal debris. The outcomes reveal the presenceof long trailing and leading tails mostly parallel to the direction of the cluster velocity vector. We found that the cluster has lost most of its mass by tidal disruption during its perigalactic passages, that lasted nearly 20 Myr each. Hence, a decrease in the density of escaping stars near the cluster is expected from our $N$-body simulations, which in turn means that stronger extra-tidal features could be found out by exploring much larger areas around NGC6891., Comment: 8 pages, 10 figures. Accepted for publication in Astronomy & Astrophysics

New star cluster candidates projected toward the Large and Small Magellanic Clouds (L/SMC) have been recently discovered from relatively deep imaging surveys. We here conduct a sound analysis of 24 star cluster candidates located in the outer regions of the L/SMC using PSF photometry produced by the Survey of the Magellanic Stellar History. With only one exception, the studied objects resulted to be genuine stellar aggregates. We conclude on their physical reality once their observed color-magnitude diagrams (CMDs) were statistically decontaminated by the presence of field stars, and the resulting cleaned CMDs for stars with assigned membership probabilities higher than 50\% were compared with synthetic CMDs generated for thousand combinations of ages, distances, metallicities, star cluster mass and binary fractions. The parameter of the best-matched synthetic CMDs obtained from a likelihood approach were adopted as the star cluster astrophysical properties. The present star cluster sample spans a wide range of distances, from those star clusters located in front of the LMC, to those along the onset of the Magellanic Bridge, up to those behind the SMC. Their ages reveal different formation episodes that took place along the galaxy formation and others as a consequence of the galaxy interactions. From their estimated metallicities and ages, we speculate with the possibility that relatively metal-deficient gaseous flows have existed between these galaxies during nearly the last one Gyr (log(age /yr) $\approx$ 9.0), that made possible the formation of young star clusters in the galaxy peripheries. Despide the L/SMC interactions, the studied star clusters are similar or more massive than their counterparts in the Milky Way, which suggests that tidal effects are relatively more important in our Galaxy., Comment: 7 figures, 8 pages. Accepted for publication in Astronomy & Astrophysics

I report outcomes of the analysis of the $A^+$ parameter, which measures the level of radial segregation of blue straggler stars in old star clusters, commonly known as the dynamical clock for the long-term internal dynamical evolution. I used $A^+$ values available in the literature for 48 Milky Way globular clusters. I found that the relationship of $A^+$ and the number of central relaxation times which have elapsed ($N_{relax}$) shows a non negligible dependence on the strength of the host galaxy gravitational potential, in addition to depending on the two-body relaxation mechanism. Indeed, a measured $A^+$ value corresponds to relatively smaller or larger $N_{relax}$ values for star clusters located farther or closer to the galaxy center. From an observational point of view, this finding reveals the possibility of disentangling for the first time the dynamical evolutionary stage due to two-body relaxation and tidal effect, that affect the whole star clusters' body concurrently., Comment: 3 pages, 1 figure. Accepted for publication in RNAAAS

Context. Extratidal stars are stellar bodies that end up outside the tidal radius of a cluster as a result of internal processes or external forces acting upon it. The presence and spatial distribution of these stars can give us insights into the past evolution of a cluster inside our Galaxy. Aims. Previous works suggest that globular clusters, when explored in detail, show evidence of extratidal stars. We aim to search for possible extratidal stars in the Galactic globular clusters NGC 6397, NGC 2808, and NGC 6266 using the photometry and proper motion measurements from Gaia DR2 database (Gaia Collaboration et al. 2018). Results. Finally, 120, 126, and 107 extratidal candidate stars were found lying outside the tidal radius of the globular clusters NGC 6397, NGC 2808, and NGC 6266, respectively. 70%, 25.4%, and 72.9% of the extratidal stars found are located outside the Jacobi radius of NGC 6397, NGC 2808, and NGC 6266, respectively. The spatial distribution of the extratidal stars belonging to NGC 6397 appears S-like, extending along the curved leading and trailing arms. NGC 2808 has an overdensity of stars in the trailing part of the cluster and NGC 6266 seems to have overdensities of extratidal stars in its eastern and northern sides. Conclusions. Proper motions and color-magnitude diagrams can be used to identify extratidal candidate stars around GCs. Nonetheless, depending on how different the kinematics and stellar populations of a cluster are compared to the Milky Way field, the fraction of contamination can be larger. All three clusters are found to have extratidal stars outside their tidal radii. For NGC 6397 and NGC 2808, these stars may be the result of a combined effect of the disc shocks and tidal disruptions. For NGC 6266, the distribution of extratidal stars is symmetrical around it, most likely indicating that the cluster has an extended stellar envelope., Comment: Accepted for publication in Astronomy and Astrophysics

We revisited the young Large Magellanic Cloud star cluster NGC1971 with the aim of providing additional clues to our understanding of its observed extended Main Sequence turnoff (eMSTO), a feature common seen in young stars clusters, which was recently argued to be caused by a real age spread similar to the cluster age (~160 Myr). We combined accurate Washington and Stromgren photometry of high membership probability stars to explore the nature of such an eMSTO. From different ad hoc defined pseudo colors we found that bluer and redder stars distributed throughout the eMSTO do not show any inhomogeneities of light and heavy-element abundances. These 'blue' and 'red' stars split into two clearly different groups only when the Washington $M$ magnitudes are employed, which delimites the number of spectral features responsible for the appearance of the eMSTO. We speculate that Be stars populate the eMSTO of NGC1971 because: i) Hbeta contributes to the M passband; ii) Hbeta emissions are common features of Be stars and; iii) Washington M and T1 magnitudes show a tight correlation; the latter measuring the observed contribution of Halpha emission line in Be stars, which in turn correlates with Hbeta emissions. As far as we are aware, this is the first observational result pointing to Hbeta emissions as the origin of eMSTOs observed in young star clusters. The presence outcome will certainly open new possibilities of studying eMSTO from photometric systems with passbands centered at features commonly seen in Be stars., Comment: 5 pages, 4 figures. Accepted for publication in Astronomy & Astrophysics

We searched for trails to understand the different Na abundances measured in first and second generation stars of ancient Milky Way globular clusters. For that purpose, we gathered from the recent literature the aforementioned Na abundances, orbital parameters, structural and internal dynamical properties and ages in an homogeneous scale of 28 globular clusters. We found that the intra-cluster Na enrichment, measured by the difference of Na abundances between first and second generation stars, exhibits a trend as a function of the Na abundances of first generation stars, in the sense that the more Na-poor the first generation stars, the larger the Na enrichment. By using the inclinations of the globular clusters' orbits, the analyzed Na enrichments also hinted at a boundary at ~0.3 dex to differentiate globular clusters with an accreted or in situ origin, the accreted globular clusters having larger Na enrichments. Because relatively larger intra-cluster Na enhancements are seen in accreted globular clusters, and small Na enhancements are observed in globular clusters formed in situ (although not exclusively), we speculate with the possibility that the amplitude of the Na enrichment could be linked with the building block paradigm. Globular clusters at the time of formation of first and second generation stars would seem to keep memory of this hierarchical galaxy formation process., Comment: 10 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

We use {\it Gaia} DR2 photometry and proper motions to search for the hypothetical tidal tails of the Galactic globular cluster E\,3. Using a modified version of a classical decontamination procedure, we are able to identify the presence of an extended structure emerging from the cluster up to $r \sim 1$\,deg from its center, thus suggesting that this poorly studied cluster is undergoing a tidal disruption process. These low surface-brightness structures are aligned with the direction to the Galactic center, as expected for a cluster close to its perigalacticon. Different scenarios to explain the important amount of mass lost by this cluster are discussed., Comment: 6 pages, 4 figures, 1 table, accepted for publication in MNRAS

We present results on the extra-tidal features of the Milky Way globular cluster NGC 7099, using deep gr photometry obtained with the Dark Energy Camera (DECam). We reached nearly 6 mag below the cluster Main Sequence (MS) turnoff, so that we dealt with the most suitable candidates to trace any stellar structure located beyond the cluster tidal radius. From star-by-star reddening corrected color-magnitude diagrams (CMDs) we defined four adjacent strips along the MS, for which we built the respective stellar density maps, once the contamination by field stars was properly removed. The resulting field star cleaned stellar density maps show a short tidal tail and some scattered debris. Such extra-tidal features are hardly detected when much shallower Gaia DR2 data sets are used and the same CMD field star cleaning procedure is applied. Indeed, by using 2.5 magnitudes below the cluster MS turnoff as the faintest limit (G < 20.5 mag), cluster members turned out to be distributed within the cluster's tidal radius, and some hints for field star density variations are found across a circle of radius 3.5deg centered on the cluster and with similar CMD features as cluster stars. The proper motion distribution of these stars is distinguishable from that of the cluster, with some superposition, which resembles that of stars located beyond 3.5deg from the cluster center., Comment: 7 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

We report results that show that the straightforwardly star cluster metallicities obtained from Str\"omgren $vby$ photometry is age-dependent and need to be corrected for further use. This outcome arises from the comparison of [Fe/H] values derived from Str\"omgren photometry with those metallicities published in the literature for 26 Large and Small Magellanic Cloud star clusters, whose ages range from $\sim$ 1 Gyr up to the known oldest globular clusters' ages in these galaxies. While deriving mean star cluster metallicities we carried out a thorough selection of red giant branch candidates to comply with the Str\"omgren metallicity calibration validity regime. We paid attention to the effect of contamination by field stars, particularly of those that lie inside the star clusters' radii, distributed along the star cluster red giant branches, and with [Fe/H] values covering a similar range as that for the selected stars. We found that the measured Str\"omgren metallicities are systematically more metal-poor than the published ones and that a quadratically age-varying function reproduces the relative metallicity values with an overall uncertainty of $\sim$ 0.05 dex. We finally performed a similar comparison relying on a fully independent approach, that consisted in using theoretical red giant branches of old globular clusters spanning [Fe/H] values from -2.0 up to 0.0 dex as standard ones. We then superimposed on to them the red giant branches of star clusters with ages in the range 1.0 - 12.5 Gyr and estimated by interpolation their associated metallicities. The derived theoretical relative metallicities follow a similar trend as a function of the star clusters' ages than that found from observations of star clusters., Comment: 10 pages, 15 figures. Accepted for publication in Astronomy and Astrophysics

We provide a homogeneous set of structural parameters of 83 star clusters located at the periphery of the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). The clusters' stellar density and surface brightness profiles were built from deep, AO assisted optical images, and uniform analysis techniques. The structural parameters were obtained from King and Elson et al. model fittings. Integrated magnitudes and masses (for a subsample) are also provided. The sample contains mostly low surface brightness clusters with distances between 4.5 and 6.5 kpc and between 1 and 6.5 kpc from the LMC and SMC centres, respectively. We analysed their spatial distribution and structural properties, comparing them with those of inner clusters. Half-light and Jacobi radii were estimated, allowing an evaluation of the Roche volume tidal filling. We found that: (i) for our sample of LMC clusters, the tidal radii are, on average, larger than those of inner clusters from previous studies; (ii) the core radii dispersion tends to be greater for LMC clusters located towards the southwest, with position angles of $\sim$200 degrees and about $\sim$5 degrees from the LMC centre, i.e., those LMC clusters nearer to the SMC; (iii) the core radius evolution for clusters with known age is similar to that of inner clusters; (iv) SMC clusters with galactocentric distances closer than 4 kpc are overfilling; (v) the recent Clouds collision did not leave marks on the LMC clusters' structure that our analysis could reveal., Comment: 19 pages, 16 figures, accepted by MNRAS. Full tables and additional plots included

There is an increasing number of recent observational results which show that some globular clusters exhibit internal rotation while they travel along their orbital trajectories around the Milky Way center. Based on these findings, we looked for any relationship between the inclination angles of the globular clusters' orbits with respect to the Milky Way plane and those of their rotation. We discovered that the relative inclination, in the sense rotation axis inclination - orbit axis inclination, is a function of the globular cluster's orbit inclination. Rotation and orbit axes are aligned for an inclination of ~ 56deg, while the rotation axis inclination is far from the orbit's one between ~ 20deg and -20deg when the latter increases from 0deg up to 90deg. We further investigated the origin of such a linear relationship and found no correlation with the semimajor axes and eccentricities of the globular clusters' orbits, nor with the internal rotation strength, the globular clusters' sizes, actual and tidally disrupted masses, half-mass relaxation times, among others. The uncovered relationship will impact on the development of numerical simulations of the internal rotation of globular clusters, on our understanding about the interaction of the globular clusters with the Milky Way gravitational field, and on the observational campaigns for increasing the number of studied globular clusters with detected internal rotation., Comment: 4 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics Letters

We report the identification of a numerous binary star population in the recently discovered ~3 Gyr old open cluster UBC 274. It becomes visible once the cluster color-magnitude diagram is corrected by differential reddening and spans mass ratios (q) values from 0.5 up to 1.0. Its stellar density radial profile and cumulative distribution as a function of the distance from the cluster's center reveal that it extends out to the observed boundaries of the cluster's tidal tails (~ 6 times the cluster's radius) following a spatial distribution indistinguishable from that of cluster Main Sequence (MS) stars. Furthermore, binary stars with q values smaller or larger than 0.75 do not show any spatial distribution difference either. From Gaia DR2 astrometric and kinematics data we computed Galactic coordinates and space velocities with respect to the cluster's center and mean cluster space velocity, respectively. We found that, cluster members located all along the tidal tails, irrespective of being a single or binary star, move relatively fast. The projection of their motions on the Galactic plane resembles that of a rotating solid body, while those along the radial direction from the Galactic center and perpendicular to the Galactic plane suggest that the cluster is being disrupted. The similarity of the spatial distributions and kinematic patterns of cluster MS and binary stars reveals that UBC 274 is facing an intense process of disruption that has apparently swept out any signature of internal dynamic evolution like mass segregation driven by two-body relaxation., Comment: 4 pages, 6 figures. Accepted for publication in Astronomy & Astrophysics

We report on the search for overall kinematical or structural conditions that have allowed some Milky Way globular clusters to presently develop tidal tails. For this purpose, we build a comprehensive catalogue of globular clusters with studies focused on their outermost regions and classified them in three categories: those with observed tidal tails, those with extra-tidal features different from tidal tails and those without any signature of extended stellar density profiles. When exploring different kinematical and structural parameter spaces, we found that globular clusters - irrespective from the presence of tidal tails, or any other kind of extra-tidal features or the absence of them - behave similarly. In general, globular clusters whose orbits are relatively more eccentric and very inclined respect to the Milky Way plane have undergone a larger amount of mass-loss by tidal disruption. The latter has also accelerated the internal dynamics toward a comparatively more advanced stage of evolution. These outcomes show that it is not straightforward to find any particular set of parameter space and dynamical conditions that can definitely predict tidal tails along globular clusters in the Milky Way., Comment: 5 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics Letters

We present results on the basis of Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relative small size and mass, there has not been yet a general consensus about the existence of extra-tidal structures around it. While some previous results claim for the absence of such features, others have shown that the cluster is under the effects of tidal stripping. From DECaLS g,r magnitudes of stars placed along the cluster Main Sequence in the colour-magnitude diagram --previously corrected by interstellar reddening--, we built the cluster stellar density map. The resulting density map shows nearly smooth contours around Pal 13 out to 1.6 times the most recent estimate of its Jacobi radius, derived by taking into account its variation along its orbital motion. This outcome favours the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disc a comparable large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of cluster mass lost., Comment: 8 pages, 6 figures. Accepted for publication in Astronomy & Astrophysics

We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal-content. However, the G versus G_BP-G_RP colour-magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H] = -0.4 dex), with a present-day mass of 3.3x10^3 Mo. The cluster exhibits an extended Main-Sequence turnoff (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation and metallicity spread yields an eMSTO of ~340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages., Comment: 7 pages, 6 figures. Accepted for publication in MNRAS

We report on the extent of the effects of the Milky Way's gravitational field in shaping the structural parameters and internal dynamics of its globular cluster population. We make use of a homogeneous, up-to-date data set with kinematics, structural properties, current and initial masses of 156 globular clusters. In general, cluster radii increase as the Milky Way potential weakens; with the core and Jacobi radii being those which increase at the slowest and fastest rate respectively. We interpret this result as the innermost regions of globular clusters being less sensitive to changes in the tidal forces with the Galactocentric distance. The Milky Way's gravitational field also seems to have differentially accelerated the internal dynamical evolution of individual clusters, with those toward the bulge appearing dynamically older. Finally we find a sub-population consisting of both compact and extended globular clusters (as defined by their rh/rJ ratio) beyond 8 kpc that appear to have lost a large fraction of their initial mass lost via disruption. Moreover, we identify a third group with rh/rJ > 0.4, which have lost an even larger fraction of their initial mass by disruption. In both cases the high fraction of mass lost is likely due to their large orbital eccentricities and inclination angles, which lead to them experiencing more tidal shocks at perigalacticon and during disc crossings. Comparing the structural and orbital parameters of individual clusters allows for constraints to be placed on whether or not their evolution was relaxation or tidally dominated., Comment: 13 pages, 7 figures. Accepted for publication in MNRAS

Since several years ago, the search for multiple populations (MPs) in Galactic open clusters (OCs) has become a field of increasing interest, particularly to the light of the general knowledge that MPs are observed in relatively massive clusters (>= 5 10^4 Mo). I report here measurements of stellar parameters and abundances of 17 different chemical species, including light and iron-peak elements of the old open cluster NGC188, from the APOGEE DR14 database. I selected 15 bonafide cluster red giants that reveal an spread in [Na/Fe] of +-0.16 dex, caused by two different groups of measurements whose mean [Na/Fe] values differ by ~ 0.30 dex. A hint for a subtle anti-correlation with Al and TiII, which also show relative large [X/Fe] dispersions, is also seen in the data. However, [Na/Fe] abundances have been found to be typically affected by uncertainties of 0.16 dex. Furthermore, I directly compared the available spectra for stars with similar atmospheric parameters and it would seem that they look similar. Therefore, I warn users of large spectroscopic surveys to be extra careful when finding peculiar abundance results. Analysis pipelines that run in an unsupervised fashion may produce bad results which may not be noticed before publication., Comment: 8 pages, 5 figures. Enlarged version of RNAAS Research Notes of the AAS 3, 104 (2019)

We report astrophysical properties of 12 Milky Way open clusters located beyond the circle around the Sun where the number of catalogued open clusters is thought to be statistically complete. By using deep optical photometry, we estimated their ages and metallicities on the basis of a maximum likelihood approach, using cluster members identified from Gaia DR2 data and likelihood procedures. The studied clusters turned out to be of intermediate-age (0.8 - 4.0 Gyr), with metallicities spanning the range [Fe/H] ~ -0.5 - +0.1 dex, and distributed within the general observed trend of the Milky Way disc radial and perpendicular metallicity gradients. As far as we are aware, these are the first metal abundance estimates derived for these clusters so far. From the constructed stellar density radial profiles and cluster mass functions we obtained a variety of structural and internal dynamics evolution parameters. They show that while the innermost cluster regions would seem to be mainly shaped according to the respective internal dynamics evolutionary stages, the outermost ones would seem to be slightly more sensitive to the Milky Way tidal field. The nearly coeval studied clusters are experiencing different levels of two-body relaxation following star evaporation; those at more advanced stages being more compact objects. Likewise, we found that the more important the Milky way tides, the larger the Jacobi volume occupied by the clusters, irrespective of their actual sizes and internal dynamics evolutionary stages., Comment: 16 pages, 9 figures. Accepted for publication in Monthly Noticies of the Royal Astronomical Society

We report results on the kinematics of Milky Way (MW) globular clusters (GCs) based on updated space velocities for nearly the entire GC population. We found that a 3D space with the semi-major axis, the eccentricity and the inclination of the orbit with respect to the MW plane as its axes is helpful in order to dig into the formation of the GC system. We find that GCs formed in-situ show a clear correlation between their eccentricities and their orbital inclination in the sense that clusters with large eccentricities also have large inclinations. These GCs also show a correlation between their distance to the MW center and their eccentricity. Accreted GCs do not exhibit a relationship between eccentricity and inclination, but span a wide variety of inclinations at eccentricities larger than ~ 0.5. Finally, we computed the velocity anisotropy "beta" of the GC system and found for GCs formed in-situ that "beta" decreases from ~ 0.8 down to 0.3 from the outermost regions towards the MW center, but remains fairly constant (0.7-0.9) for accreted ones. These findings can be explained if GCs formed from gas that collapsed radially in the outskirts, with preference for relative high infall angles. As the material reached the rotating forming disk, it became more circular and moved with lower inclination relative to the disk. A half of the GC population was accreted and deposited in orbits covering the entire range of energies from the outer halo to the bulge., Comment: 8 pages, 5 figures. Accepted for publication in The Astrophysical Journal

The study of dynamical properties of Galactic open clusters is a fundamental prerequisite for the comprehension of their dissolution processes. In this work, we characterized 12 open clusters, namely: Collinder 258, NGC 6756, Czernik 37, NGC 5381, Ruprecht 111, Ruprecht 102, NGC 6249, Basel 5, Ruprecht 97, Trumpler 25, ESO 129-SC32 and BH 150, projected against dense stellar fields. In order to do that, we employed Washington $CT_{1}$ photometry and GAIA DR2 astrometry, combined with a decontamination algorithm applied to the three-dimensional astrometric space of proper motions and parallaxes. From the derived membership likelihoods, we built decontaminated colour-magnitude diagrams, while structural parameters were obtained from King profiles fitting. Our analysis revealed that they are relatively young open clusters (log($t$ yr$^{-1}$) $\sim7.3-8.6$), placed along the Sagittarius spiral arm, and at different internal dynamical stages. We found that the half-light radius to Jacobi radius ratio, the concentration parameter and the age to relaxation time ratio describe satisfactorily their different stages of dynamical evolution. Those relative more dynamically evolved open clusters have apparently experienced more important low-mass star loss., Comment: Accepted for publication in MNRAS 19 pages, 10 figures

We present results on the stellar density radial profile of the outer regions of NGC6779, a Milky Way globular cluster recently proposed as a candidate member of the Gaia Sausage structure, a merger remnant of a massive dwarf galaxy with the Milky Way. Taking advantage of the Pan-STARRS PS1 public astrometric and photometric catalogue, we built the radial profile for the outermost cluster regions using horizontal branch and main sequence stars, separately, in order to probe for different profile trends because of difference stellar masses. Owing to its relatively close location to the Galactic plane, we have carefully treated the chosen colour-magnitude regions properly correcting them by the amount of interstellar extinction measured along the line-of-side of each star, as well as cleaned them from the variable field star contamination observed across the cluster field. In the region spanning from the tidal to the Jacobi radii the resulting radial profiles show a diffuse extended halo, with an average power law slope of -1. While analysing the relationships between the Galactocentric distance, the half-mass density, the half-light radius, the slope of the radial profile of the outermost regions, the internal dynamical evolutionary stage, among others, we found that NGC6779 shows structural properties similar to those of the remaining Gaia Sausage candidate globular clusters, namely, they are massive clusters (>10^5Mo) in a moderately early dynamical evolutionary stage, with observed extra-tidal structures., Comment: 8 pages, 6 figures. Accepted for publication in Monthly Noticies of the Royal Astronomical Society

The VISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA) Survey is an ongoing project based on deep photometric observations of Magellanic Cloud star clusters, collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. Since 2015 more than 200 hours of telescope time were used to observe about 130 stellar clusters, most of them with low mass (M < 10$^4$ M$_\odot$) and/or located in the outermost regions of the Large Magellanic Cloud and the Small Magellanic Cloud. With this high quality data set, we homogeneously determine physical properties from statistical analysis of colour-magnitude diagrams, radial density profiles, luminosity functions and mass functions. Ages, metallicities, reddening, distances, present-day masses, mass function slopes and structural parameters for these clusters are derived and used as a proxy to investigate the interplay between the environment in the Magellanic Clouds and the evolution of such systems. In this first paper we present the VISCACHA Survey and its initial results, concerning the SMC clusters AM3, K37, HW20 and NGC796 and the LMC ones KMHK228, OHSC3, SL576, SL61 and SL897, chosen to compose a representative subset of our cluster sample. The project's long term goals and legacy to the community are also addressed., Comment: 21 pages, 21 figures

We report results of proper motions of 15 known Large Magellanic Cloud (LMC) old globular clusters (GCs) derived from the Gaia DR2 data sets. When these mean proper motions are gathered with existent radial velocity measurements to compose the GCs' velocity vectors, we found that the projection of the velocity vectors onto the LMC plane and those perpendicular to it tell us about two distinct kinematic GC populations. Such a distinction becomes clear if the GCs are split at a perpendicular velocity of 10 km/s (absolute value). The two different kinematic groups also exhibit different spatial distributions. Those with smaller vertical velocities are part of the LMC disc, while those with larger values are closely distributed like a spherical component. Since GCs in both kinematic-structural components share similar ages and metallicities, we speculate with the possibility that their origins could have occurred through a fast collapse that formed halo and disc concurrently., Comment: 5 pages, 2 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society Letters

We present results obtained from Stromgren photometry of 13 young (~30-220 Myr) Magellanic Cloud (MC) clusters, most of them lacking in the literature from direct metallicity measurements. We derived for them [Fe/H] values from a high-dispersion spectroscopy-based empirical calibration of the Stromgren metallicity sensitive index m1 for yellow and red supergiants (SGs). Particular care was given while estimating their respective uncertainties. In order to obtain the mean cluster metallicities, we used [Fe/H] values of selected SGs for which we required to be located within the cluster radii, placed in the expected SG region in the cluster colour-magnitude diagrams, and with [Fe/H] values within the FWHM of the observed cluster metallicity distributions. The resulting metallicities for nearly 75 per cent of the cluster sample agree well with the most frequently used values of the mean MCs' present-day metallicities. The remaining clusters have mean [Fe/H] values that fall near the edge of the MC present-day metallicity distributions. When comparing the cluster metallicities with their present positions, we found evidence that supports the claimed recent interaction of the MCs with the Milky Way, that could have caused that some clusters were scattered from their birthplaces. Indeed, we show examples of clusters with metal contents typical of the galaxy inner regions placed outward them. Likewise, we found young clusters, at present located in the inner regions of both MCs, formed out of gas that has remained unmixed since several Gyr ago., Comment: 10 pages, 2 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We report on the spread of [Fe/H] values in the massive Large Magellanic Cloud cluster NGC1978, recently confirmed to harbor multiple populations of nearly the same age. We used accurate Stromgren photometry of carefully selected cluster red giant branch stars along with a high-dispersion spectroscopy-based calibration of the metallicity-sensitive index m1. Once accounting for the photometry quality, assessed from extensive artificial stars tests to trace the photometric uncertainties as a function of the position to the cluster's center as well as the stellar brightness, and those from the metallicity calibration, we found that NGC1978 exhibits a small metallicity spread of 0.035 dex (+- 0.019-0.023), depending on whether stars with individual sigma[Fe/H] < 0.15 dex or those located in the cluster's outer areas are considered. Such a spread in [Fe/H] is consistent with a cluster formation model with self-enrichment, if mass loss higher than 90 per cent due to stellar evolutionary and galactic tidal effects is assumed. Nevertheless, scenarios where the apparent [Fe/H] variation reflects CN abundance anomalies or less extreme mass loss models with environmentally-dependent self enrichment should not be ruled out., Comment: 11 pages, 4 figures. Accepted for publication in The Astronomical Journal

We present results from photometric and spectroscopic data obtained with SOAR and Gemini observatory facilities in the field of a recently discovered star cluster. The cluster, projected towards the Eastern side of the outer disc of the Large Magellanic Cloud (LMC), was originally placed nearly 10 kpc behind the LMC with an age and metallicity typical of the innermost LMC star cluster population. We assigned radial velocity (RV) memberships to stars observed spectroscopically, and derived the cluster age and distance from theoretical isochrone fitting to the cluster colour-magnitude diagram. The new object turned out to be a 0.9 Gyr old outer LMC disc cluster, which possibly reached the present position after being scattered from the innermost LMC regions where it might have been born. We arrived at this conclusion by examining the spatial distribution of LMC star clusters of similar age, by comparing the derived spectroscopic metallicity with that expected for an outside-in galaxy formation scenario, by considering the cluster internal dynamical stage as inferred from its derived structural parameters and by estimating the circular velocity of a disc that rotates with the corresponding star cluster radial velocity at the cluster's deprojected distance, which resulted to be nearly 60 per cent higher than that of most of the outer LMC disc clusters., Comment: 9 pages, 8 figures. Accepted for publication in Monthly Noticies of the Royal Astronomical Society