We investigate, for the first time, the formation and evolution of the tidal tail released from a young Pleiades-like star cluster due to expulsion of primordial gas in a realistic gravitational field of the Galaxy. The tidal tails (as well as clusters) are integrated by nbody6 from their embedded phase for more than 300 Myr. We vary the star formation efficiency (SFE) from 33% to 100% and the timescales of gas expulsion as free parameters, and provide predictions for the morphology and kinematics of the evolved tail for each of the models. The resulting tail properties are intended for comparison with Gaia measurements, where an inverse analysis of our findings might constrain some of the poorly understood conditions and processes in embedded star clusters during the gas phase and gas expulsion.

Star clusters are often born as star-cluster systems, which include several stellar clumps. Such star-cluster complexes could have formed from turbulent molecular clouds. Since Gaia Data Release 2 provided us high quality velocity data of individual stars in known star-cluster complexes, we now can compare the velocity structures of the observed star-cluster complexes with simulated ones. We performed a series of N-body simulations for the formation of star-cluster complexes starting from turbulent molecular clouds. We measured the inter-cluster velocity dispersions of our simulated star-cluster complexes and compared them with the Carina region and NGC 2264. We found that the Carina region and NGC 2264 formed from molecular clouds with a mass of ∼4 × 105M⊙ and ∼4 × 104M⊙, respectively. In our simulations, we also found that the maximum cluster mass (Mc,max) in the complex follows ${M_{{\rm{c}},{\rm{max}}}} = 0.{\rm{2}}0M_g^{0.76}$, where Mg is the initial gas mass.

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.

Gravitational wave direct detections suggest that 30 M⊙ binary black holes (BBHs) commonly exist in the universe. One possible formation scenario of such BBHs is dynamical three-body encounters in dense star clusters. We performed a series of direct N-body simulations with a mass of 2500 and 10000 M⊙ and found a new channel for the formation of BBHs which is dominant in open clusters. In open clusters, the core-collapse time is shorter than in globular clusters, and therefore massive main-sequence (MS) binaries can form before they evolve to BHs. These MS binaries experience common envelope evolution and evolve to hard BBHs, which can merge within the Hubble time. The number of BBH mergers per unit mass obtained from our simulations reached 20–50 % of that for globular clusters, assuming an initial cluster mass function. Thus, open clusters can be a dominant formation site of hard BBHs.

Stars form predominantly in groups which display a broad spectrum of masses, sizes, and other properties. Despite this diversity there exist an underlying structure that can constrain cluster formation theories. We show how combining observations with simulations allows us to disclose this underlying structure. One example is the mass-radius relation for young embedded associations which follows ${M_c} = CR_c^\gamma $ with γ = 1.7 ± 0.2.0.2, which is directly related to the mass-radius relation of clumps. Results based on GAIA DR2 have demonstrated that young stellar groups (1–5 Myr) expand and that this expansion process is largely over by an age of 10–20 Myr. Such a behaviour is expected within the gas expulsion scenario. However, the effect of gas expulsion depends strongly on the SFE, the gas expulsion time scale, etc. Here it is demonstrated how existing and upcoming data are able to constrain these parameters and correspondingly the underlying models.

Setting the formation of globular clusters (GCs) within a cosmological context and characterising the properties of proto-GCs at high redshift is currently a major challenge. In this work, we address that challenge by exploring a suit of high-resolution cosmological simulations from the First Billion Years (FiBY) project z at ⩾6 to investigate theoretical scenarios concerning the formation of old, low-mass stellar systems with a particular focus on GCs. Two distinct groups of objects are identified in the simulations. The first group of objects, with a high baryon fraction, we associate with proto-GCs. The second group, that exhibit a high stellar fraction, could be forming ultra-faint dwarf galaxies (UFDs). The objects with high baryon fraction are promising proto-GC candidates because they have little to no dark matter (DM), have number densities consistent with predictions from the literature, are very compact and have a high stellar density. We fit and also assess the redshift-zero globular system mass - halo mass relation and find it provides a reasonable fit to our proto-GC objects, indicating that this relation is likely set at formation.

We present a model for hydrodynamic + N-body simulations of star cluster formation and evolution using AMUSE. Our model includes gas dynamics, star formation in regions of dense gas, stellar evolution and a galactic tidal spiral potential, thus incorporating most of the processes that play a role in the evolution of star clusters.

We test our model on initial conditions of two colliding molecular clouds as well as a section of a spiral arm from a previous galaxy simulation.

We study runaway stellar collisions in primordial star clusters and formation of intermediate mass black holes (IMBHs). Using cosmological simulations, we identify eight atomic-cooling halos in which the star clusters form. We follow stellar and dark matter (DM) dynamics for 3Myr using hybrid N-body simulations. We find that the runaway stellar collisions occur in all star clusters and IMBHs with masses ∼400–1900M⊙ form. Performing additional N-body simulations, we explore evolutions of the IMBHs in the star clusters for 15 Myr. The IMBH masses grow via stellar tidal disruption events (TDEs) to ∼700–2500 M⊙. The TDE rates are ∼0.3–1.3 Myr−1. DM motions affect the star cluster evolutions and reduce the TDE rates. The IMBHs may subsequently grow to SMBHs by gas supply through galaxy mergers or large-scale gas inflows, or they may remain within or around the clusters.

In this work we present our new estimates of the fundamental parameters of the open cluster Collinder 463, based on Gaia astrometric and PanSTARRS photometric data. In addition to updating previously available parameter values we highlight the existence of an extended stellar “halo” which is closely related to the presently known star cluster.

We present a detailed analysis of the projected stellar rotational velocities of the well-separated double main sequence (MS) in the young, ∼200 Myr-old Milky Way open cluster NGC 2287 and suggest that stellar rotation may drive the split MSs in NGC 2287. We find that the observed distribution of projected stellar rotation velocities could result from a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster’s member stars in stellar binary systems. The slow rotators are likely stars that initially rotated rapidly but subsequently slowed down through tidal locking induced by low-mass-ratio binary systems. However, the cluster may have a much larger population of short-period binaries than is usually seen in the literature, with relatively low secondary masses.

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.

We review spectroscopic results concerning multiple stellar populations in globular clusters. The cluster initial mass is the most important parameter determining the fraction of second generation stars. The threshold for the onset of the multiple population phenomenon is 1–3×105 M⊙. Nucleosynthesis is influenced by metallicity: Na/O and Mg/Al anti-correlations are more extended in metal-poor than in metal-rich clusters. Massive clusters are more complex systems than the smaller ones, with several populations characterized by different chemical compositions. The high Li abundance observed in the intermediate second generation stars strongly favours intermediate mass AGB stars as polluters for this class of stars; however, it is well possible that the polluters of extreme second generation stars, that often do not have measurable Li, may be fast rotating massive stars or super-massive stars. The mass budget factor should be a function of the cluster mass, and needs to be large only in massive clusters.

I review the methods, mostly developed in the last decade, that are commonly used to identify and characterize multiple populations (MPs) in Globular Clusters (GCs) based on photometry. I summarize the results from the recent surveys of MPs with the Hubble Space Telescope (HST) and ground-based facilities and provide a list of the main properties of MPs as inferred from these studies.

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.

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.

. We present a significantly improved version of our numerical code JASMINE, that can now solve the Jeans equations for axisymmetric models of stellar systems, composed of an arbitrary number of stellar populations, a Dark Matter halo, and a central Black Hole. The stellar components can have different structural (density profile, flattening, mass, scale length), dynamical (rotational support, velocity dispersion anisotropy), and population (age, metallicity, Initial Mass Function, mass-to-light ratio) properties. These models, when combined with observations, will allow to investigate important issues, such as quantifying the systematic effects of IMF variations, of mass-to-light ratio gradients, and of different stellar kinematic components (e.g. counter rotating disks, kinematically decoupled cores) on luminosity-weighted properties. The developed analytical and numerical framework aims at modeling Early-Type Galaxies, but it can also be applied to dwarf Spheroidal galaxies and Globular Clusters.

Recent analyses of Lee et al. (2018, 2019) have confirmed that Galactic bulge consists of stellar populations originated from Milky Way globular clusters (MWGCs). Motivated by this, here we present the evolutionary population synthesis (EPS) for the Galactic bulge and early-type galaxies (ETGs) with the realistic treatment of individual variations in light elements observed in the MWGCs. We have utilized our model with GC-origin populations to explain the CN spread observed in ETGs, and the results show remarkable matches with the observations. We further employ our model to estimate the age of ETGs, which are considered as good analogs for the MW bulge. We find that, without the effect of our new treatments, EPS models will almost always underestimate the true age of ETGs. Our analysis indicates that the EPS with GC-origin populations is an essential constraint in determining the ETG formation epoch and is closely related to understanding the evolution of the Universe.

The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity dispersion, seems to be related to the initial configuration of the system. In recent work (Milone et al. 2018), we analyzed for the first time the kinematics of the different stellar populations in NGC 0104 (47 Tucanae) over a large field of view, exploiting the Gaia Data Release 2 proper motions combined with multi-band ground-based photometry. In this paper, based on the work by Cordoni et al. (2019), we extend this analysis to six GCs, namely NGC 0288, NGC 5904 (M 5), NGC 6121 (M 4), NGC 6752, NGC 6838 (M 71) and further explore NGC 0104. Among the analyzed clusters only NGC 0104 and NGC 5904 show significant rotation on the plane of the sky. Interestingly, multiple stellar populations in NGC 5904 exhibit different rotation curves.

Present-day structural and kinematical properties of multiple populations (MPs) can provide useful information about the physical mechanisms driving the formation and early evolution of globular clusters (GCs). As part of a large project aimed at characterizing the kinematics of MPs, here we present a detailed multi-epoch analysis of the low-mass GC NGC6362. We find that MPs in this system show significant differences in their line-of-sight velocity dispersion profiles. This result is totally unexpected given the dynamical age and fraction of mass lost by NGC6362. We also find that the binary fraction is remarkably larger in the first (FP) than in the second population (SP). We show that such a difference can efficiently inflate the velocity dispersion of FP at intermediate/large cluster-centric distances with respect to SP. Indeed, our results nicely match the predictions of state-of-the art N-body simulations of the co-evolution of MPs in GCs including the effect of binaries.