We present several results of the study of the evolution of globular clusters’ internal kinematics, as driven by two-body relaxation and the interplay between internal angular momentum and the external Galactic tidal field. Via a large suite of N-body simulations, we explored the three-dimensional velocity space of tidally perturbed clusters, by characterizing their degree of velocity dispersion anisotropy and their rotational properties. These studies have shown that a cluster’s kinematical properties contain distinct imprints of the cluster’s initial structural properties, dynamical history, and tidal environment. Building on this fundamental understanding, we then studied the dynamics of multiple stellar populations in globular clusters, with attention to the largely unexplored role of angular momentum.

I will present results obtained by means of three-dimensional hydrodynamic simulations of the formation of second generation (SG) stars in a young globular cluster (GC). Our setup includes the mass return from Asymptotic Giant branch (AGB) stars, the accretion of pristine gas as well as star formation of SG stars, three ingredients which have never been simultaneously taken into account in previous 3D numerical studies of GC formation. The cluster is set in motion with respect to a distribution of gas and allowed to accrete mass from it. Formation of SG stars occurs out of the gas shed by AGB stars and from the gas accreted during the motion of the cluster. We consider two models characterised by different densities of the external gas. In both cases, we find that a very compact SG subsystem with central density > 105M⊙/pc3 forms in the innermost regions of the cluster.

Since a great number of star stream and substructures near M31/M33 have been discovered in Pan-Andromeda Archaeological Survey (PAndAS) and variations of star stream density may trace the dark matter sub-halos, it is good opportunity to study the dark matter sub-halos with the star streams. Further it has been proved that dozens of halo star clusters have the relations with the star stream. As Prime Focus Spectroscopy (PFS) of the 8.2-m Subaru telescope have the powerful ability (I ∼ 22.3 mag) to observe ∼ 2400 objects at a time, it can be used to observe the giant star streams, faint halo star clusters and dwarf galaxies, which provides excellent opportunity to investigate the sub-halos of M31. In addition, we are involved with the Local Volume Mapper (LVM) of SDSS-V program, which may also provide more informations for the star clusters of the Local Group, especially for M31. Finally since we have done series of work with Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), we will continue the spectroscopic observations for more star clusters and giant stars of M31/M33.

Looking for variable stars in the M31 dwarf spheroidal satellite Andromeda XXV (And XXV), which we have observed with the LBC at the LBT, we serendipitously discovered a clustering of stars (Gep I) of 12 arcsec in diameter, near the center of And XXV. This is one of the very few clusters known to be associated with a dwarf spheroidal galaxy. The half light radius (rh) of Gep I at the distance of And XXV corresponds to 25 pc in linear extension. Radius and absolute V (MV∼ −4.9 mag) magnitude place Gep I in the region of the MV-rh plane that seems to be forbidden to ordinary globular clusters (GCs). The seeing-limited resolution of our photometry could resolve only a few bright stars in Gep I. The CMD of these sources is compatible with an old stellar population placed at a heliocentric distance of ∼750–800 kpc, thus confirming a real concentration of old stars. The ground-based CMD of Gep I is severely incomplete. Future high resolution imaging and spectroscopy of the brightest stars will permit to disentangle the puzzle on the real nature of Gep I.

In recent years, we have gathered enough evidence showing that most of the Galactic globular clusters extend well beyond their King tidal radii and fill their Jacobi radii in the form of “extended stellar haloes”. In some cases, because of the interaction with the Milky Way, stars are able to exceed the Jacobi radius, generating tidal tails which may be used to trace the mass distribution in the Galaxy. In this work, we use the precious information provided by the space mission Gaia (photometry, parallaxes and proper motions) to analyze NGC 362 in the search for member stars in its surroundings. Our preliminar results suggest that it is possible to identify member stars and tidal features up to distances of a few degrees from the globular cluster center.

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The origin of the chemical anomalies in star clusters is still an open question, although much effort has been employed both from a theoretical and observational point of view. The exploration of the dependence of such multiple stellar populations based on certain cluster properties (e.g. mass, age, metallicity) has represented a compelling line of investigation so far. Here I report an overview of the results obtained from our latest surveys aimed at characterising the phenomenon of chemical variations in star clusters that are much younger with respect to the ancient globular clusters. The fundamental question we are asking is whether these abundance patterns are only restricted to the old massive clusters; and if not, is there a difference between young and old objects?

NGC 6402 is one of the most massive globular clusters in the Galaxy but until recently little was known about its detailed chemical composition. Interestingly, recent results have shown that NGC 6402 exhibits a paucity of intermediate composition stars that may be indicative of an early termination of star formation. As a result, NGC 6402 may be important for understanding cluster formation and the order in which various stellar populations are born.

I present the latest results from our group about the multiple stellar populations in the old Milky Way globular clusters (GCs) and in the young systems both in the Magellanic Clouds and in the Milky Way. For the ancient GCs in our Galaxy I summarize the chemical properties of the stellar populations as observed on the chromosome map. Both Type I and Type II GCs are discussed. For the youngest clusters I will briefly report our latest spectroscopic analysis on the Large Magellanic Cloud cluster NGC 1818 and the Galactic open cluster M 11, which supports the co-existence of stellar populations with different rotation rates.

Recently, the sample size of stars with detailed, homogeneous abundances in the massive bulge Globular cluster NGC 6388 expanded to 185 giants. We use this wealth of data to present first results on its multiple stellar populations. In particular, i) we introduce a new diagnostic plot to survey the occurrence of very high temperature for H-burning in the first-generation polluters, and ii) we pinpoint a restricted temperature range reached by polluters at work in NGC 6388.

We present the study of horizontal branch morphology of the cluster NGC 6656. A blueward shift in temperature of about ~5000 K (nM-jump) in the color-color plot is detected.To explain this feature, we study the presence of stellar-mass black hole by plotting Projected density profile (PDP) in the central HST region. The PDP in the inner region (r < 10″) can be nicely reproduced by the king+BH model. The blue ward shift in temperature can be due the presence of stellar mass black holes in the centre.

Young star clusters (YSCs) with resolved stellar populations are well suited for studying star-cluster formation. In most cases, the (pre-main-sequence) stellar populations found in the YSCs are coeval with an intrinsic age spread of up to 1Myr. Such observations can be understood as the YSCs having formed in one burst, which star formation was truncated by stellar feedback. The recent discovery that the colour-magnitude diagram of the Orion Nebula Clusters (ONC) contains three well defined age-separated populations appears to shatter this model. The implication is that the ONC formed in three bursts, with star formation still on-going in the last burst. We present new observational results focusing on the three populations in the ONC using OmegaCAM photometry and Gaia DR2 measurements. We also describe a theoretical model which may explain these observations by an interplay between stellar feedback and cluster dynamics.

We summarize the results from a study of the globular cluster (GC) system of the isolated elliptical galaxy NGC 6411, based on Gemini/GMOS g', r', i’ photometry. The extent of the globular cluster system is about 70 kpc. It contains ≍700 members. The colour distribution and luminosity function are typical of old GC systems. An excess of bright GCs with intermediate colours might evidence an intermediate-age merger.

Nuclear star clusters are found at the centers of most galaxies. They are the densest stellar systems in the Universe, and thus have unique and interesting stellar dynamics. We review how common nuclear star clusters are in galaxies of different masses and types, and then discuss the typical properties of NSCs. We close by discussing the formation of NSCs, and how a picture is emerging of different formation mechanisms being dominant in lower and higher mass galaxies.

Several observational and theoretical studies suggest that the initial mass function (IMF) slope for massive stars in globular clusters (GCs) depends on the initial cloud density and metallicity, such that the IMF becomes increasingly top-heavy with decreasing metallicity and increasing the gas density of the forming object. Using N-body simulations of GCs starting with a top-heavy IMF and undergo early gas expulsion within a Milky Way-like potential, we show how such a cluster would evolve. By varying the degree of top-heaviness, we calculate the dissolution time and the minimum cluster mass needed for the cluster to survive after 12 Gyr of evolution.

The second data release of the Gaia mission coupled with ground-based spectroscopic observations has allowed the determination of the orbital parameters for almost all of the Galactic globular clusters, as well as for the known dwarf spheroidal galaxies orbiting the Milky Way. Moreover, it has led to the discovery of dwarf galaxies that were accreted by the Galaxy long ago and that are now completely disrupted. By exploiting their dynamics in combination with the globular clusters age-metallicity relation, we investigated the clusters-to-dwarfs connection. We found that about 60 globulars likely formed in situ, and associated those that were accreted to the dwarf galaxy progenitor they likely formed in.

A vast number of observed galactic nuclei are known to harbour a central supermassive black hole (SMBH). In their early lifetime, these systems might have witnessed the strong interaction between the SMBH and massive star clusters formed in the inner galactic regions. Due to the strong tidal field exerted from the SMBH, clusters are likely to undergo tidal disruption, releasing their stars all around the SMBH, and possibly driving the formation of a nuclear cluster (NC). This mechanism can contribute to populate galactic nuclei with intermediate-mass black holes (IMBH). Interactions with the central SMBH can lead to the formation of tight massive BH binaries (MBBH) that undergo coalescence via gravitational waves (GW) emission. We discuss this mechanism in the context of the Milky Way centre, exploring the possibility that SgrA*, the Galactic SMBH, has an IMBH companion.

Our Galaxy and the nearby Andromeda Galaxy (M31) form a bound system, even though the relative velocity vector of M31 is currently not well constrained. Their orbital motion is highly dependent on the initial conditions, but all the reliable scenarios imply a first close approach in the next 3–5 Gyrs. In our study, we simulate this interaction via direct N-body integration, using the HiGPUs code. Our aim is to investigate the dependence of the time of the merger on the physical and dynamical properties of the system. Finally, we study the dynamical evolution of the two Supermassive Black Holes placed in the two galactic centers, with the future aim to achieve a proper resolution to follow their motion until they form a tight binary system.

We present a brief summary of the results of a study of the effects of dynamical evolution on the stellar mass function of multiple-population globular clusters. Theoretical studies have predicted that the process of multiple-population cluster formation results in a system in which second-generation (2G) stars are initially more centrally concentrated than first-generation (1G) stars. In the study presented here, we have explored the implications of the initial differences between the 2G and 1G structural properties for the evolution of the local (measured at different distances from a cluster center) and global mass function. We have studied both systems in which 1G and 2G stars start with the same initial mass function (IMF) and systems in which 1G and 2G stars have different IMFs. Finally we have explored the evolution of the spatial mixing and found that the multiscale nature of the clusters studied leads to a dependence of the mixing rate on the stellar mass.

The identification of young massive star clusters (YMCs) at high redshift is becoming a real fact. We present recent results from Hubble deep imaging and VLT/ MUSE - X-Shooter observations boosted by strong gravitational lensing. We report on two parsec-scale star-forming systems at z = 6.145 and 2.37 (>10 Gyrs of look back time) currently representing the best candidate high-z YMCs. All of this also implies that the search for globular cluster precursors has already begun.