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We present the first large-scale 3D kinematic study of |$\sim$| 2700 spectroscopically confirmed young stars (⁠|$\lt $| 20 Myr) in 18 star clusters and OB associations (hereafter groups) from the combination of Gaia astrometry and Gaia –ESO Survey spectroscopy. We measure 3D velocity dispersions for all groups, which range from 0.61 to 7.4 km s |$^{-1}$| (1D velocity dispersions of 0.35–4.3 km s |$^{-1}$| ). We find the majority of groups have anisotropic velocity dispersions, suggesting they are not dynamically relaxed. From the 3D velocity dispersions, measured radii, and estimates of total mass, we estimate the virial state and find that all systems are super-virial when only the stellar mass is considered, but that some systems are sub-virial when the mass of the molecular cloud is taken into account. We observe an approximately linear correlation between the 3D velocity dispersion and the group mass, which would imply that the virial state of groups scales as the square root of the group mass. However, we do not observe a strong correlation between virial state and group mass. In agreement with their virial state, we find that nearly all of the groups studied are in the process of expanding and that the expansion is anisotropic, implying that groups were not spherical prior to expansion. One group, Rho Oph, is found to be contracting and in a sub-virial state (when the mass of the surrounding molecular cloud is considered). This work provides a glimpse of the potential of the combination of Gaia and data from the next generation of spectroscopic surveys. [ABSTRACT FROM AUTHOR]

Cosmic ray acceleration at the termination shock of compact star clusters has recently received much attention, mainly because of the detection of gamma-ray emission from some of such astrophysical sources. Here we focus on the acceleration of nuclei at the termination shock and we investigate the role played by proton energy losses and spallation reactions of nuclei, especially downstream of the shock. We show that for a reasonable choice of the mean gas density in the cavity excavated by the cluster wind, dominated by the presence of dense clouds, the spectrum of He nuclei escaping the bubble is systematically harder than the spectrum of hydrogen, in a manner that appears to be qualitatively consistent with the observed and yet unexplained phenomenon of discrepant hardening. We also find that, in this scenario, the spallation reactions of heavier nuclei are likely to be so severe that their spectra becomes very hard and with a low normalization, meaning that it is unlikely that heavy nuclei escaping star clusters can provide a sizeable contribution to the spectrum of cosmic rays at the Earth. Limitations and implications of this scenario are discussed. [ABSTRACT FROM AUTHOR]

The physical properties of star cluster populations offer valuable insights into their birth, evolution, and disruption. However, individual stars in clusters beyond the nearest neighbours of the Milky Way are unresolved, forcing analyses of star cluster demographics to rely on integrated light, a process fraught with uncertainty. Here, we infer the demographics of the cluster population in the benchmark galaxy NGC 628 using data from the Legacy Extra-galactic UV Survey (LEGUS) coupled to a novel Bayesian forward-modelling technique. Our method analyses all 1178 clusters in the LEGUS catalogue, |$\sim 4$| times more than prior studies severely affected by completeness cuts. Our results indicate that the cluster mass function is either significantly steeper than the commonly observed slope of |$-2$| or is truncated at |$\approx 10^{4.5}$| M |$_\odot$|⁠ ; the latter possibility is consistent with proposed relations between truncation mass and star formation surface density. We find that cluster disruption is relatively mild for the first |$\approx 200$|   Myr of cluster evolution; no evidence for mass-dependent disruption is found. We find suggestive but not incontrovertible evidence that inner galaxy clusters may be more prone to disruption and outer galaxy clusters have a more truncated mass function, but confirming or refuting these findings will require larger samples from future observations of outer galaxy clusters. Finally, we find that current stellar track and atmosphere models, along with common forms for cluster mass and age distributions, cannot fully capture all features in the multidimensional photometric distribution of star clusters. While our forward-modelling approach outperforms earlier backward-modelling approaches, some systematic differences persist between observed and modelled photometric distributions. [ABSTRACT FROM AUTHOR]

Motivated by the recent JWST discovery of galaxy overdensities during the Epoch of Reionzation, we examine the physical properties of high- z protoclusters and their evolution using the Full-hydro Large-scale structure simulations with All-sky Mapping for the Interpretation of Next Generation Observations (FLAMINGO) simulation suite. We investigate the impact of the apertures used to define protoclusters, because the heterogeneous apertures used in the literature have limited our understanding of the population. Our results are insensitive to the uncertainties of the subgrid models at a given resolution, whereas further investigation into the dependence on numerical resolution is needed. When considering galaxies more massive than |$M_\ast \, {\simeq }\, 10^8\, {\rm M_\odot }$|⁠ , the FLAMINGO simulations predict a dominant contribution from progenitors similar to those of the Coma cluster to the cosmic star formation rate density during the reionization epoch. Our results indicate the onset of suppression of star formation in the protocluster environments as early as |$z\, {\simeq }\, 5$|⁠. The galaxy number density profiles are similar to NFW (Navarro–Frenk–White profile) at |$z\, {\lesssim }\, 1$| while showing a steeper slope at earlier times before the formation of the core. Different from most previous simulations, the predicted star formation history for individual protoclusters is in good agreement with observations. We demonstrate that, depending on the aperture, the integrated physical properties including the total (dark matter and baryonic) mass can be biased by a factor of 2 to 5 at |$z\, {=}\, 5.5$| –7, and by an order of magnitude at |$z\, {\lesssim }\, 4$|⁠. This correction suffices to remove the |${\simeq }\, 3\, \sigma$| tensions with the number density of structures found in recent JWST observations. [ABSTRACT FROM AUTHOR]

The relation between nuclear star clusters (NSCs) and the growth of the central supermassive black holes (SMBHs), as well as their connection to the properties of the host galaxies, is crucial for understanding the evolution of galaxies. Recent observations have revealed that about 10 per cent of nucleated galaxies host hybrid nuclei, consisting of both NSCs and accreting SMBHs that power active galactic nuclei (AGNs). Motivated by the potential of the recently published multiwavelength data sets from LeMMINGs survey, here we present the most thorough investigation to date of the incidence of hybrid nuclei in a large sample of 100 nearby nucleated galaxies (10 E, 25 S0, 63 S, and 2 Irr), covering a wide range in stellar mass (⁠|$M_{*,\rm gal} \sim 10^{8.7}-10^{12}~\rm M_{\odot }$|⁠). We identify the nuclei and derive their properties by performing detailed 1D and 2D multicomponent decompositions of the optical and near-infrared HST stellar light distributions of the galaxies using Sérsic and core-Sérsic models. Our AGN diagnostics are based on homogeneously derived nuclear 1.5 GHz e -MERLIN radio, Chandra X-ray (0.3–10 keV), and optical emission-line data. We determine the nucleation fraction (⁠|$f_{\rm nuc}$|⁠) as the relative incidence of nuclei across the LeMMINGs HST sample and find |$f_{\rm nuc} =~$| 100/149 (= 67 |$\pm$| 7 per cent), confirming previous work, with a peak value of |$49/56~(= 88 \pm 13$|  per cent) at bulge masses |$M_{*,\rm bulge}\sim 10^{9.4}- 10^{10.8}~ \rm M_{\odot }$|⁠. We identify 30 nucleated LeMMINGs galaxies that are optically active, radio-detected, and X-ray luminous (⁠|$L_\textnormal {X} \gt 10^{39}$| erg s |$^{-1}$|⁠). This indicates that our nucleated sample has a lower limit |$\sim$| 30 per cent occupancy of hybrid nuclei, which is a function of |$M_{*,\rm bulge}$| and |$M_{*,\rm gal}$|⁠. We find that hybrid nuclei have a number density of |$(1.5 \pm 0.4)\times 10^{-5}$|  Mpc |$^{-3}$|⁠ , are more common at |$M_{*,\rm gal}\sim 10^{10.6}- 10^{11.8}~\rm M_{\odot }$| and occur, at least, three times more frequently than previously reported. [ABSTRACT FROM AUTHOR]

We study the wide-binary eccentricity (e) distribution in young star clusters and the role of turbulence in setting the form of the e distribution using magnetohydrodynamical simulations of star cluster formation. The simulations incorporate gravity, turbulence, magnetic fields, protostellar heating, and jets/outflows. We find that (1) simulations that employ purely compressive turbulence driving produce binaries with a superthermal e distribution [ |$\alpha \gt 1$| in |$p(e) \propto e^\alpha$| ], while simulations with purely solenoidal driving or natural mixture of driving modes produce subthermal/thermal distributions (⁠|$\alpha \le$| 1), (2) the e distribution over the full range of binary separations in our simulations is set at the early stages of the star cluster formation process, (3) while binaries (separation of |$r_{\mathrm{pair}} \le 1000\, \mathrm{AU}$|⁠) have subthermal to thermal e distributions (⁠|$\alpha \sim 0.8$|⁠), wide binaries (⁠|$r_{\mathrm{pair}} \gt 1000\, \mathrm{AU}$|⁠) have a superthermal distribution (⁠|$\alpha \sim 1.8$|⁠), and (4) low-mass binary systems (system masses of |$M_{\mathrm{sys}} \le 0.8\, \mathrm{M_\odot }$|⁠) have a highly superthermal distribution (⁠|$\alpha \sim 2.4$|⁠), whereas high-mass systems (⁠|$M_{\mathrm{sys}} \gt 0.8\, \mathrm{M_\odot }$|⁠) exhibit a subthermal/thermal distribution (⁠|$\alpha \sim 0.8$|⁠). The binary eccentricity distribution is often modelled as a thermal distribution. However, our results suggest that the e distribution depends on the range of separation of the sampled binaries, which agrees with the findings from recent Gaia observations. We conclude that the dependence of the e distribution on the binary separation and mass is linked to the binary formation mechanism governed by the turbulent properties of the parent cloud. [ABSTRACT FROM AUTHOR]

We perform a large-scale hydrodynamic simulation of a massive star cluster whose stellar population mimics that of the Cygnus OB2 association. The main-sequence stars are first simulated during 1.6 Myr, until a quasi-stationary state is reached. At this time, the three Wolf–Rayet stars observed in Cygnus OB2 are added to the simulation, which continues to 2 Myr. Using a high-resolution grid in the centre of the domain, we can resolve the most massive stars individually, which allows us to probe the kinetic structures at small (parsec) scales. We find that, although the cluster excavates a spherical 'superbubble' cavity, the stellar population is too loosely distributed to blow a large-scale cluster wind termination shock, and that collective effects from wind–wind interactions are much less efficient than usually assumed. This challenges our understanding of the ultra-high energy emission observed from the region. [ABSTRACT FROM AUTHOR]

We analyse the GeV γ-ray emission from the W3 complex using about 14 years of Pass 8 data recorded by the Fermi Large Area Telescope (Fermi -LAT). We resolve the γ-ray emissions around W3 into two components: an elliptical Gaussian overlapping with the molecular gas and a point-like source near the cluster W3 Main. The pion-bump feature of SED for the elliptical Gaussian together with the better fitting result of pion decay model favour the hadronic origin. We further argue that the cosmic rays (CRs) could originate from the interactions between cluster winds and the shock produced by the SNR HB3. The point-like source positionally coincident with the star cluster W3 Main indicates it may be directly powered by near clusters, while its fainter γ-ray emissions below 10 GeV are possibly due to the shelter from dense gas making the low-energy CRs incapable of penetrating the dense materials. Meanwhile, we cannot rule out that the γ-ray emissions originate from the interaction of accelerated protons in SNR with the ambient gas. [ABSTRACT FROM AUTHOR]

The origin of extended main-sequence turn-offs (eMSTO) in star clusters younger than 2 Gyr still challenges our current understanding of stellar evolution. Exploiting data from Gaia Data Release 3 (DR3), we investigate eMSTOs in a large sample of 32 Galactic open clusters younger than 2.4 Gyr. We first validate Gaia rotational velocities from radial velocity spectrometer spectra by comparing them with literature values and assessing their correlation with magnetic activity measurements from LAMOST spectra. We detect a general positive correlation between turn-off colour and projected stellar rotation, with slow-rotating stars predominantly found on the bluer side of the turn-off. Comparing our observations with theoretical models, we find that the eMSTO morphology is well reproduced by a single population formed with a high rotation rate, and observed with rotation axis inclination ranging between 0° (pole-on) and 90° (edge-on). This contrasts with observations of Magellanic Cloud clusters, where a population of non-rotating stars appears to be ubiquitous in clusters younger than 700 Myr. However, we note that our interpretation, while successfully explaining the overall eMSTO morphology, cannot fully explain the observed projected rotational velocities. Additionally, two young clusters, NGC 3532 and NGC 2287, exhibit moderate evidence of a split-main sequence in colour and rotation, suggesting a possible small spread in the initial rotation rate. Finally, we advise caution in determining the ages of young clusters from non-rotating isochrones, as neglecting the effects of stellar rotation can impact the isochrone dating by up to factors of 5–20 per cent. [ABSTRACT FROM AUTHOR]

Photometric completeness affects the photometry of stars in crowded regions such as the cores of star clusters. Some analysis such as deriving the structural parameters of star clusters using radial density profile is heavily affected by photometric completeness and the classical techniques to map this completeness in a given field are very expensive computationally. In most surveys, for example, the large quantity of data makes it impracticable to estimate the completeness using the traditional method for the whole sample due to time and computational requirements. In this work, we present a new method that is significantly faster and results in similar completeness curves and maps as the traditional approach, providing a great first-step completeness estimator for a large sample of data. Using the completeness corrected data for each cluster we built radial density profiles improving significantly the inner portion of the profile; we also fitted the King model to them, determining the clusters' structural parameters based on a more realistic cluster profile. In this preliminary analysis, we derived structural parameters for nine selected clusters covering a range of core radii (5–40 arcesc) and tidal radii (40–180 arcesc) and discuss how the photometric completeness affects the determination of these parameters when we count stars to trace the radial profile of a star cluster. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive multiwavelength investigation of the intermediate-age open cluster NGC 1912. We identified 401 member stars for NGC 1912 using K-nearest neighbour and Gaussian Mixture Model machine learning techniques. The fundamental parameters determined for the cluster are metallicity (z) = 0.0141 |$\pm$| 0.0006, log(age) = 8.519 |$\pm$| 0.040, binary fraction (⁠|$b_{\text{frac}}$|⁠) = 0.445 |$\pm$| 0.035, visual extinction (⁠|$A_V$|⁠) = 0.864 |$\pm$| 0.033 mag, total-to-selective extinction ratio (⁠|$R_V$|⁠) = 3.007 |$\pm$| 0.096, distance = 1096 |$\pm$| 15 pc. The central density (⁠|$\rho _o$|⁠), core radius (⁠|$r_c$|⁠), tidal radius (⁠|$r_t$|⁠), and background density (⁠|$\rho _{\mathrm{bg}}$|⁠) for the cluster are obtained as 0.643 |$\pm$| 0.067 stars arcmin |$^{-2}$| , 7.743 |$\pm$| 0.784 arcmin, 84.633 |$\pm$| 7.188 arcmin, and 0.001 |$\pm$| 0.000 stars arcmin |$^{-2}$| , respectively. Dynamical mass segregation study revealed a concentration of some apparently massive stars towards the cluster centre. Polarimetric analysis of 90 stars in |$BVR_cI_c$| wavelength bands revealed that the observed polarization in NGC 1912 is not solely attributed to interstellar dust. The Galactic magnetic field is dominant in this region. Dust grain sizes within the intracluster region are found to be relatively smaller than that of the general ISM. The extinction map revealed the existence of a potential 'interstellar bubble' located close to the cluster region. Towards the periphery of the probable bubble region, which displays an ovoid-like geometry, 16 probable young stellar objects have been detected, suggesting the ongoing triggering of secondary star formation events in this region. [ABSTRACT FROM AUTHOR]

The chemical abundances of Milky Way's (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most satellites are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in satellites than are currently available. To correctly extract SFHs from large samples of chemical abundances, the relationship between chemical abundances and SFHs needs to be clarified. Here, we perform a high-resolution cosmological zoom-in simulation of a MW-like galaxy with detailed models of star formation, supernova (SN) feedback, and metal diffusion. We quantify SFHs, metallicity distribution functions, and the α -element (Mg, Ca, and Si) abundances in satellites of the host galaxy. We find that star formation in most simulated satellites is quenched before infalling to their host. Star formation episodes in simulated satellites are separated by a few hundred Myr owing to SN feedback; each star formation event produces groups of stars with similar [ α /Fe] and [Fe/H]. We then perform a mock observation of the upcoming Subaru Prime Focus Spectrograph (PFS) observations. We find that Subaru PFS will be able to detect distinct groups of stars in [ α /Fe] versus [Fe/H] space, produced by episodic star formation. This result means that episodic SFHs can be estimated from the chemical abundances of ≳1000 stars determined with medium-resolution spectroscopy. [ABSTRACT FROM AUTHOR]

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Exploring the marks left by galactic accretion in the Milky Way helps us understand how our Galaxy was formed. However, finding and studying accreted stars and the galaxies they came from has been challenging. This study uses a simulation from the Numerical Investigation of a Hundred Astronomical Objects project, which now includes a wider range of chemical compositions, to find better ways to spot these accreted stars. By comparing our findings with data from the GALAH spectroscopic survey, we confirm that the observationally established diagnostics of [Al/Fe] versus [Mg/Mn] also show a separation of in situ and accreted stars in the simulation, but stars from different accretion events tend to overlap in this plane even without observational uncertainties. Looking at the relationship between stellar age and linear or logarithmic abundances, such as [Fe/H], we can clearly separate different groups of these stars if the uncertainties in their chemical makeup are less than 0.15 dex and less than 20 per cent for their ages. This method shows promise for studying the history of the Milky Way and other galaxies. Our work highlights how important it is to have accurate measurements of stellar ages and chemical content. It also shows how simulations can help us understand the complex process of galaxies merging and suggest how these events might relate to the differences we see between our Galaxy's thin and thick disc stars. This study provides a way to compare theoretical models with real observations, opening new paths for research in both our own Galaxy and beyond. [ABSTRACT FROM AUTHOR]

Origin of LIGO/Virgo gravitational wave events may involve production of binaries with relativistic components in dense stellar systems – globular or nuclear star clusters – and their subsequent evolution towards merger. Orbital parameters of these binaries (the inner orbit) and their motion inside the cluster (the outer orbit) evolve due to both external agents – random encounters with cluster stars and cluster tides due to the smooth cluster potential – and the internal ones – various sources of dissipation and precession within the binary. We present a numerical framework – binary evolution in stellar clusters (besc) – that follows the evolution of the binary inner and outer orbits accounting for all these effects simultaneously, enabling efficient Monte Carlo studies. The secular effect of cluster tides is computed in the singly averaged approximation, without averaging over the outer binary orbit. As to stellar encounters, we include the effects of both close and distant flybys on the inner and outer orbits of the binary, respectively. Also, given our focus on the LIGO/Virgo sources, we include the general relativistic precession (which suppresses cluster tides at high eccentricities) and the gravitational wave emission (shrinking the binary orbit). We use besc to illustrate a number of characteristic binary evolutionary outcomes and discuss relative contributions of different physical processes. In particular, we find that stellar encounters often dominate over the cluster tides in the evolution of compact binaries. besc can also be used to study other objects in clusters, e.g. blue stragglers, hot Jupiters, X-ray binaries, etc. [ABSTRACT FROM AUTHOR]

In our previous work, we introduced a method that combines two unsupervised algorithms: Density-based spatial clustering of applications with noise (DBSCAN) and Gaussian mixture model (GMM). We applied this method to 12 open clusters based on Gaia Early Data Release 3 (EDR3) data, demonstrating its effectiveness in identifying reliable cluster members within the tidal radius. However, for studying cluster morphology, we need a method capable of detecting members both inside and outside the tidal radius. By incorporating a supervised algorithm into our approach, we successfully identified members beyond the tidal radius. In our current work, we initially applied DBSCAN and GMM to identify reliable members of cluster stars. Subsequently, we trained the random forest algorithm using DBSCAN- and GMM-selected data. Leveraging the random forest, we can identify cluster members outside the tidal radius and observe cluster morphology across a wide field of view. Our method was then applied to 15 open clusters based on Gaia DR3, which exhibit a wide range of metallicity, distances, members, and ages. Additionally, we calculated the tidal radius for each of the 15 clusters using the King profile and detected stars both inside and outside this radius. Finally, we investigated mass segregation and luminosity distribution within the clusters. Overall, our approach significantly improved the estimation of the tidal radius and detection of mass segregation compared to the previous work. We found that in Collinder 463, low-mass stars do not segregate in comparison to high-mass and intermediate-mass stars. Additionally, we detected a peak of luminosity in the clusters, some of which were located far from the centre, beyond the tidal radius. [ABSTRACT FROM AUTHOR]

The dispersion relation of the magnetized Kelvin–Helmholtz (KH) instability driven by shear flow with zero thickness of the shear layer is derived theoretically based on a set of magnetohydrodynamic equations in the presence of a transverse magnetic field and a radiation field. The influence of the magnetic field strength, the radiation field strength, and the density ratio of the two sides of the shear layer on KH instability is analyzed by solving the dispersion equation. The results indicate that the presence of radiation and transverse magnetic fields can destabilize the KH instability due to the resulting increase in Mach number, which in turn reduces the compressibility of the system. Also, the extent of the destabilizing effect of the magnetic field can be affected by the magnetoacoustic Mach number M 1 f and the Mach number M 2. The growth rates vary more significantly for relatively small values of both parameters. Finally, the stabilizing effect of a large density ratio is considered, and it is found that as the density ratio increases, the effect of the radiation field is more significant at larger Mach number M 2. These results can be applied to astrophysical phenomena with velocity shear, such as flows across the transition layer between an H ii region and a molecular cloud, accretion flows, and shear flows of cosmic plasmas. [ABSTRACT FROM AUTHOR]

JWST observations of galaxies at z ≳ 8 suggest that they are more luminous and clumpier than predicted by most models, prompting several proposals on the physics of star formation and feedback in the first galaxies. In this paper, we focus on the role of ultraviolet (UV) radiation in regulating star formation by performing a set of cosmological radiation hydrodynamics simulations of one galaxy at subparsec resolution with different radiative feedback models. We find that the suppression of cooling by far-UV (FUV) radiation (i.e., H2 dissociating radiation) from Population II stars is the main physical process triggering the formation of compact and massive star clusters and is responsible for the bursty star formation observed in metal-poor galaxies at z ≳ 10. Indeed, artificially suppressing FUV radiation leads to a less intense continuous mode of star formation distributed into numerous but low-mass open star clusters. Due to the intense FUV field, low-metallicity clouds remain warm (∼104 K) until they reach a relatively high density (≳103 cm−3), before becoming self-shielded and transitioning to a colder (∼100 K), partially molecular phase. As a result, star formation is delayed until the clouds accumulate enough mass to become gravitationally unstable. At this point, the clouds undergo rapid star formation, converting gas into stars with high efficiency. We therefore observe exceptionally bright galaxies (10 times brighter than for continuous star formation) and subsequent quenched "dead" galaxies that did not form stars for tens of Myr. [ABSTRACT FROM AUTHOR]

Bubbles driven by energy and mass injection from small scales are ubiquitous in astrophysical fluid systems and essential to feedback across multiple scales. In particular, O stars in young clusters produce high-velocity winds that create hot bubbles in the surrounding gas. We demonstrate that the dynamical evolution of these bubbles is critically dependent upon the geometry of their interfaces with their surroundings and the nature of heat transport across these interfaces. These factors together determine the amount of energy that can be lost from the interior through cooling at the interface, which in turn determines the ability of the bubble to do work on its surroundings. We further demonstrate that the scales relevant to physical dissipation across this interface are extremely difficult to resolve in global numerical simulations of bubbles for parameter values of interest. This means the dissipation driving evolution of these bubbles in numerical simulations is often of a numerical nature. We describe the physical and numerical principles that determine the level of dissipation in these simulations; we use this, along with a fractal model for the geometry of the interfaces, to explain differences in convergence behavior between hydrodynamical and magnetohydrodynamical simulations presented here. We additionally derive an expression for momentum as a function of bubble radius expected when the relevant dissipative scales are resolved and show that it still results in efficiently cooled solutions, as postulated in previous work. [ABSTRACT FROM AUTHOR]

In this paper, we revise dynamical constraint on primordial black hole (PBH) abundance following the effect of their interaction with stellar cluster in dwarf galaxy Eridanus II in case of PBH clustering. We consider scattering of stars on PBH cluster as a whole, dynamical friction of stars inside cluster and finally we are taking into account tidal forces’ effects due to the finite size of PBH cluster. We obtain the rate of change of kinetic energy of the stars and PBHs to make conclusion about constraints on clusters. [ABSTRACT FROM AUTHOR]

We present a detailed study of the centre of NGC 4654, a Milky Way-like spiral galaxy in the Virgo cluster that has been reported to host a double stellar nucleus, thus promising a rare view of ongoing star cluster infall into a galaxy nucleus. Analysing JWST NIRSpec integral-field spectroscopic data in combination with Hubble Space Telescope Wide Field Camera 3 imaging of the inner 330 × 330 pc, we find that the NGC 4645 nucleus is in fact more complex than previously thought, harbouring three massive star clusters within 32 pc of the centre. Maps of infrared emission lines in the NIRSpec spectra show different morphologies for the ionised and molecular gas components. The emission from molecular hydrogen gas is concentrated at the nuclear star cluster (NSC) location, while emission from hydrogen recombination lines is more extended beyond the central cluster. The velocity fields of both gas and stars indicate that the three clusters are part of a complicated dynamical system, with the NSC having an elevated velocity dispersion in line with its high stellar mass. To investigate the stellar populations of the three clusters in more detail, we used surface brightness modelling to measure their fluxes from UV to mid-infrared wavelengths. This information, together with spectroscopically derived extinction values, are then used to fit the spectral energy distributions (SEDs) of the clusters. Two of the clusters are UV-bright and well described by single stellar populations with young ages (∼3 and 5 Myr) and relatively low masses (M* ∼ 4 × 104 M⊙ and M* ∼ 105 M⊙, respectively), whereas the central cluster is much more massive (M* = 3 × 107 M⊙), and cannot be fitted by a single stellar population. Instead, we find that the presence of a minor young population (∼1 Myr, M* ∼ 3 × 104 M⊙) embedded in a dominant old population (∼8 Gyr) is required to explain its SED. Given its complex composition and the close proximity of two young star clusters that are likely to merge with it within a few hundred million years, we consider the nucleus of NGC 4654 a unique laboratory to study NSC growth from both in situ star formation and the infall of star clusters. [ABSTRACT FROM AUTHOR]

Globular cluster (GC) stars composed of pristine material, also known as first-generation (1G) stars, are not chemically homogeneous as they exhibit extended sequences in the chromosome map (ChM). Recent studies characterized 1G stars within the center of 55 Galactic GCs, revealing metallicity variations. Despite this progress, several unanswered questions persist, particularly concerning the link between the 1G metallicity spread and factors such as the radial distance from the cluster center or the host GC parameters. Additionally, it remains unclear whether the extended 1G sequence phenomenon is exclusive to old Galactic GCs with multiple populations. This work addresses these open issues, examining 1G stars in different environments. First, we combine Hubble Space Telescope (HST) and James Webb Space Telescope photometry of the GC 47 Tucanae to study 1G stars at increasing distances from the cluster center. We find that metal-rich 1G stars are more centrally concentrated than metal-poor ones, suggesting a metallicity radial gradient. Additionally, the two groups of 1G stars share similar kinematics. Since our analysis focuses on giant stars in the cluster center and M dwarfs in external fields, we discuss the possibility that the metallicity distribution depends on stellar mass. Subsequently, we analyze HST multi-band photometry of two simple-population clusters, NGC 6791 and NGC 1783, revealing elongated sequences in the ChM associated with metallicity variations. Finally, we investigate the 1G color distribution in 51 GCs, finding no connections with the host cluster parameters. These results shed light on the complex nature of 1G stars, providing insights into the GC formation environment. [ABSTRACT FROM AUTHOR]

Context. The photometric observations from the recent decade revolutionized our view on classical pulsators. Low-amplitude signals have been detected photometrically in addition to the dominant high-amplitude radial mode pulsations in many RR Lyrae stars and classical Cepheids. First-overtone pulsators with an additional low-amplitude signal at a period ratio of around 0.61 with the main mode, the so-called 0.61 stars, form the most populous group among these stars. The nature of this signal has been attributed to non-radial pulsations. Another mysterious group are stars in which the additional signal forms a period ratio of around 0.68. These are the 0.68 stars. The origin of the signal remains unknown. Aims. Here, we search for similar phenomena in spectroscopic observations of first-overtone classical Cepheids collected as part of the VELOCE project. Methods. We performed a frequency analysis of several parameters derived from cross-correlation functions (CCFs), including radial velocity, the full width at half maximum, the bisector inverse span, and the CCF depth (contrast). Using standard pre-whitening, we searched for additional low-amplitude signals. We identified the location of these stars in various sequences of the Petersen diagram. Results. We detect additional signals in four first-overtone classical Cepheids: BG Cru, QZ Nor, V0391 Nor, and V0411 Lac. We classified BG Cru, QZ Nor, and V0391 Nor as 0.61 stars based on their period ratios. V0411 Lac, however, exhibits a ratio of 0.68 between the two modes, and the additional signal has a longer period. This type of multi-periodicity remains unexplained. Conclusions.VELOCE CCFs yield the first spectroscopic detections of non-radial pulsation modes in classical Cepheids. This opens an asteroseismic window for pursuing a more detailed understanding of these important stars. While the 0.61 signal of BG Cru, QZ Nor, and V0391 Nor is understood to originate from non-radial modes of moderate degrees, the 0.68 signal of V0411 Lac still lacks a physical explanation. [ABSTRACT FROM AUTHOR]

Context. Compact groups of galaxies are unique places where galaxy-galaxy interactions play a mayor role on the evolution of its members. These strong gravitational encounters can induce star formation bursts. Aims. We study the properties of one of the most luminous so-called hinge clumps that is located in the compact group of galaxies NGC 6845. Methods. Using integral field spectroscopy from GMOS/Gemini complemented with archival MUSE data, we obtained oxygen abundances, ages, star formation rates, and velocity fields, and we also modeled a single stellar population to understand the star formation history of the hinge clump in NGC 6845. Results. We found that the hinge clump sits in a tailthat has a star formation rate of 3.4 M⊙ yr−1, which is comparable with a few other extreme cases, for instance, the star clusters in the Antennae galaxy and other reported hinge clumps in the literature. This clump represents ∼15% of total star formation rate of NGC 6845A. Large-scale modeling of the observed velocity field of NGC 6845A rules out the scenario according to which this hinge clump was a satellite galaxy. Its kinematics is compatible with that of the galactic disk of NGC 6845A. Its abundance with a mean value of 0.4 Z⊙ is also consistent with the metallicity gradient of the galaxy. Conclusions. Our analysis suggest that the hinge clump is formed by multiple stellar populations and not by a single burst. This causes the wide age range. We found that the central clump is encompassed by a ring-like structure, which might suggest a second generation of star formation. In addition, the analysis of the diagnostic diagram indicates that this central region might also be ionized by shocks from stellar and supernova winds. Finally, the derived star formation rate density Σ = 9.7 M⊙ yr−1 kpc−2 of the central clump places it in starburst regime, where gas inflows should provide gas to maintain the star formation. This work shows a resolved example of an extreme localized starburst in a compact group of galaxies. [ABSTRACT FROM AUTHOR]

Context. Recent molecular surveys have revealed the rich gas organization of sonic-like filaments at small scales (so-called fibers) in all types of environments prior to the formation of low- and high-mass stars. These fibers form at the end of the turbulent cascade and are identified as the fine substructure within the hierarchical nature of the gas in the interstellar medium (ISM). Aims. Isolated fibers provide the subsonic conditions for the formation of low-mass stars. This paper introduces the Emergence of high-mass stars in complex fiber networks (EMERGE) project, which investigates whether complex fiber arrangements (networks) can also explain the origin of high-mass stars and clusters. Methods. We analyzed the EMERGE Early ALMA Survey including seven star-forming regions in Orion (OMC-1,2,3, and 4 South, LDN 1641N, NGC 2023, and the Flame Nebula) that were homogeneously surveyed in three molecular lines (N2H+J = 1–0, HNC J = 1–0, and HC3N J = 10–9) and in the 3 mm continuum using a combination of interferometric ALMA mosaics and IRAM-30 m single-dish (SD) maps, together with a series of Herschel, Spitzer, and WISE archival data. We also developed a systematic data reduction framework allowing the massive data processing of ALMA observations. Results. We obtained independent continuum maps and spectral cubes for all our targets and molecular lines at different (SD and interferometric) resolutions, and we explored multiple data combination techniques. Based on our low-resolution (SD) observations (30″ or ~12 000 au), we describe the global properties of our sample, which covers a wide range of physical conditions, including low-(OMC-4 South and NGC 2023), intermediate (OMC-2, OMC-3, and LDN 1641N), and high-mass (OMC-1 and Flame Nebula) star-forming regions in different evolutionary stages. The comparison between our single-dish maps and ancillary YSO catalogs denotes N2H+ (1–0) as the best proxy for the dense, star-forming gas in our targets, which show a constant star formation efficiency and a fast time evolution of ≲1 Myr. While apparently clumpy and filamentary in our SD data, all targets show a much more complex fibrous substructure at the enhanced resolution of our combined ALMA+IRAM-30 m maps (4″.5 or ~2000 au). A large number of filamentary features at subparsec scales are clearly recognized in the high-density gas (≳ 105 cm−3) that is traced by N2H+ (1–0) directly connected to the formation of individual protostars. Surprisingly, this complex gas organization appears to extend farther into the more diffuse gas (~103−104 cm−3) traced by HNC (1–0). Conclusions. This paper presents the EMERGE Early ALMA Survey, which includes a first data release of continuum maps and spectral products for this project that are to be analysed in future papers of this series. A first look at these results illustrates the need of advanced data combination techniques between high-resolution interferometric (ALMA) and high-sensitivity, low-resolution single-dish (IRAM-30 m) datasets to investigate the intrinsic multiscale, gas structure of the ISM. [ABSTRACT FROM AUTHOR]

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. [ABSTRACT FROM AUTHOR]

Context. A large number of globular clusters in the Milky Way have been studied in recent years, especially in hidden regions such as those of the Galactic bulge. Aims. The main goal of this work is to understand what we can learn if we include these new objects into the Milky Way globular cluster (GC) system that we know today. We compiled a catalog of 37 recently discovered globular clusters. Most of them are located in the Galactic bulge, but we also included some of the GCs for comparison. Methods. We used a range of distributions for investigating the Galactic GC system based on the metallicity, luminosity function, and age. We considered three samples. We first treated the new GC sample separately from the known and well characterized GCs. Consequently, we merged these two samples, thereby upgrading the Milky Way GC system. Furthermore, we performed a comparison between our clusters sample and the field star population. Results. We found a double-peaked distribution for the luminosity function, which shows an elongated faint end tail. Considering the "merged" sample, the luminosity function peaks at MVup = −7.00 ± 1.3 M V up = − 7.00 ± 1.3 $ M_{V}^{\mathrm{up}} = -7.00 \pm 1.3 $ mag and at MVup = −4.1 ± 0.48 M V up = − 4.1 ± 0.48 $ M_{V}^{\mathrm{up}} = -4.1 \pm 0.48 $ mag. The metallicity distributions also display a bimodality trend. In this case, we compare our new sample compilation with previously published ones, finding that the distributions are in good general agreement. We also constructed the metallicity distribution for the field star sample and, by comparing it with that of the GCs, we learned that a high percentage of field stars show [Fe/H] > 0; whereas we did not detect any GCs in the same metallicity range. To understand this inconsistency, we constructed the age–metallicity diagram for both samples, noting that the old and metal-poor population (age ≥ 8 Gyr and [Fe/H] ≤ −1.0) is represented by Gcs, while the young and metal-rich population (age < 8 Gyr and [Fe/H] > −1.0) corresponds to field stars. Conclusions. From the analysis of the GC luminosity function and metallicity distribution, we can conclude that many GCs, probably those that are very faint, have survived strong dynamical processes that are typical of the bulge regions. Moreover, we cannot exclude the possibility that some of them have been accreted during past merging events, especially the metal-poor component, whereas the metal-rich population may be related to the formation of the bulge and/or disk. Finally, the difference that we notice between the cluster and field star samples should be explored in the context of the evolutionary differences among these two stellar populations. [ABSTRACT FROM AUTHOR]

The Spitzer instability leads to the formation of a black hole subsystem (BHSub) at the centre of a star cluster providing energy to luminous stars (LSs) and increasing their rate of evaporation. When the self-depletion time of the BHSub exceeds the evaporation time of the LSs, a dark star cluster (DSC) will appear. Using the nbody7 code, we performed a comprehensive set of direct N -body simulations over a wide range of initial conditions to study the pure effect of the top-heaviness of the initial mass function (IMF) on the formation of the DSC phase. In the Galactic tidal field, top-heavy IMFs lead to the fast evaporation of LSs and the formation of DSCs. Therefore, DSCs can be present even in the outer region of the Milky Way (MW). To successfully transition to the DSC phase, the MW Globular Clusters (GCs) must possess an initial black hole (BH) mass fraction of |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\gt 0.05$|⁠. For star clusters with |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\gt 0.08$|⁠ , the DSC phase will be created for any given initial density of the cluster and Galactocentric distance. The duration of the cluster's lifetime spent in the DSC phase shows a negative (positive) correlation with the initial density, and Galactocentric distance of the star cluster if |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\le 0.12$| (⁠|$\widetilde {\mathit {M}}_\mathrm{BH}(0)\ge 0.15$|⁠). Considering the canonical IMF, it is unlikely for any MW GCs to enter the DSC phase. We discuss the BH retention fraction in view of the observed properties of the GCs of the MW. [ABSTRACT FROM AUTHOR]

This paper presents maps of the J=2-1 transition of CO towards the Draco nebula intermediate-velocity cloud (IVC). The maps cover 8500 square arcmin with a velocity resolution of 0.33 km s |$^{-1}$| and angular resolution of 38 |${\rm arcsec}$|⁠ , or 0.11 pc at the cloud distance of 600 pc. The mapped area includes all the emission detected by the Herschel satellite with 250 |$\mu$| m intensity >5 MJy sr−1. Previously published observations of the far-infrared (far-IR) emission and the 21 cm line of HI are used to derive the column density distribution of H |$_2$| and the abundance ratio CO/H |$_2$|⁠ , as well as the distribution of the molecular fraction of hydrogen, which approaches 90 per cent over much of the brighter parts of the nebula. The CO emission is highly clumpy and closely resembles the structures seen in far-IR images. The kinematics of the CO show supersonic motions between clumps but near-thermal to trans-sonic motions within clumps, consistent with model predictions that the scale length for dissipation of supersonic turbulence should be |$\sim 0.1$| pc, mediated by kinematic viscosity and/or ambipolar diffusion. Different parts of the nebula show evidence for a spread of molecular formation time-scales of a few 10 |$^5$| yr, comparable with the dynamical time-scale of the infalling gas. The IVC will likely merge with the Galactic interstellar medium in |$\sim 10^7$| yr, and the densest clumps may form an unbound cluster of low-mass stars. [ABSTRACT FROM AUTHOR]

The advent of JWST now allows entire star cluster populations to be imaged in galaxies at cosmologically significant redshifts, bringing with it the need to apply K -corrections to their magnitudes and colour indices. Since the stellar populations within star clusters can be well approximated by a single age and metallicity, their spectral energy distributions are very different from those of galaxies or supernovae, and their K -corrections behave differently. We derive the photometric K -corrections versus redshift for model star clusters that cover a wide range of ages and metallicities, illustrating the results particularly for the broad-band filters on the Hubble Space Telescope /Advanced Camera for Surveys and the JWST /Near-Infrared Camera that are most commonly being used for imaging of populations of star clusters in distant galaxies. In an appendix, we introduce a webtool called rescuer (REdshifted Star ClUstERs) that can generate K -values and their uncertainties for any user-defined combination of cluster properties. [ABSTRACT FROM AUTHOR]

This paper investigates the evolutionary phases of a collapsing dissipative star cluster in the presence of dark matter. For this purpose, the minimal coupling model of f(R,T) gravity is used as a candidate for exotic matter in star cluster. The collapse equation is derived from generalized dynamical equations which show the total conservation of energy within the cluster. In this context, the approach of Misner and Sharp is applied to study the phenomenon and differentiate between homologous as well as non-homologous gravitational collapse. The generalized dynamical equations are also connected to modified heat transport equations related to heat flux, viscosity and shear, which deals with Israel–Stewart theory (without removing the thermodynamics heat/viscous coupling coefficients). It is found that shear-free and non-dissipative fluid give homologous collapse. The dissipation of collapsing star cluster provides a relation between tidal forces and density inhomogeneity. It is theoretically predicted that the presence of exotic matter controlled the collapsing mechanism. [ABSTRACT FROM AUTHOR]

This paper discusses the B?ohm-Vitense gap, a gap in the colours of stars that occurs when the atmosphere changes from radiative to convective in deep layers. We are using different algorithms for detecting gaps in colour-magnitude diagrams (CMDs), including the k-nearest neighbours (k-NN) and UniDip algorithms. We propose using a combination of the k-NN algorithm and the UniDip algorithm and manual verification to identify gaps unlikely to be of a statistical origin. Using the Gaia photometric system, i.e. BP - RP, we took the data of 130 star clusters and searched for gaps in the ranges of 0.40 to 0.47mag, and 0.56 to 0.60mag, respectively. We analysed all data statistically and identified the gaps in the individual clusters. Finally, we applied the kernel density estimator to see how the gaps are distributed. [ABSTRACT FROM AUTHOR]

This paper proposes a new order parameter model which satisfactorily explains complicated symmetry changes, the temperature–pressure (T–P) phase diagram and elastic anomalies observed experimentally with the improper ferroelastic phase transitions in multiferroic KMnF3 single crystal. First, it is shown that the order parameter model is transformed according to the four‐dimensional reducible representation of the wavevector star channel group. Second, based on the order parameter model and the singularity theory, the sixth‐order structurally stable Landau potential model is constructed. Finally, the theoretical T–P phase diagram is plotted and the elastic anomalies possible for each of the phase transitions are discussed. [ABSTRACT FROM AUTHOR]

Observations and high-resolution hydrodynamical simulations indicate that massive star clusters assemble hierarchically from subclusters with a universal power-law cluster mass function. We study the consequences of such assembly for the formation of intermediate-mass black holes (IMBHs) at low metallicities (Z  = 0.01 Z⊙) with our updated N -body code bifrost based on the hierarchical fourth-order forward integrator. bifrost integrates few-body systems using secular and regularized techniques including post-Newtonian equations of motion up to order PN3.5 and gravitational-wave recoil kicks for BHs. Single stellar evolution is treated using the fast population synthesis code sevn. We evolve three cluster assembly regions with N tot = 1.70–2.35 × 106 stars following a realistic IMF in ∼1000 subclusters for t  = 50 Myr. IMBHs with masses up to m • ∼ 2200 M⊙ form rapidly mainly via the collapse of very massive stars (VMSs) assembled through repeated collisions of massive stars followed by growth through tidal disruption events and BH mergers. No IMBHs originate from the stars in the initially most massive clusters. We explain this by suppression of hard massive star binary formation at high velocity dispersions and the competition between core collapse and massive star lifetimes. Later the IMBHs form subsystems resulting in gravitational-wave BH–BH, IMBH–BH, and IMBH–IMBH mergers with a m • ∼ 1000 M⊙ gravitational-wave detection being the observable prediction. Our simulations indicate that the hierarchical formation of massive star clusters in metal poor environments naturally results in formation of potential seeds for supermassive black holes. [ABSTRACT FROM AUTHOR]

We derive astrophysical parameters of the open cluster NGC 1513 by means of colour indices built with new CCD  UBV (RI) KC photometry. Based on early-type members, the mean foreground reddening and total to selective extinction ratio are E (B − V) = 0.79 ± 0.09 mag and RV = 2.85 ± 0.05. Through the differential grid method, we derive the metal abundance [Fe/H] = −0.06 dex (Z = +0.013), which is consistent with the value [Fe/H] = −0.088 of the bright giant member – LAMOST 695710060. Z = +0.013 isochrone fit to the V × (B − V) colour–magnitude diagram leads to a turn-off age of 224 ± 27 Myr (thus an intermediate-age cluster), and a distance modulus of (V 0 − MV) = 10.90 ± 0.15 mag, thus implying a distance from the Sun d = 1514 ± 105 pc. Within the uncertainties, our photometric distance is consistent with the value d = 1435 ± 14 pc from the Gaia DR3 parallax. We find signs of small mass segregation through a minimum spanning tree analysis for the 190 most massive stars, together with the rather steep mass function (χ = +2.39) slope. The high core to half-light radius ratio R core/ R h = 0.82, together with the compact half-light to tidal radius ratio R h/ R t = 0.22, suggest that it is probably related to cluster-formation effects, due to little dynamical evolution, instead of driving its dynamical evolution by internal relaxation. Indeed, NGC 1513 is located in the second quadrant (ℓ = 152 |${_{.}^{\circ}}$| 59 and Galactocentric distance R GC = 9.57 kpc), which tends to minimize tidal effects by external processes and tidal disruption. Therefore, internal mass segregation effects in NGC 1513 seem to be more efficient than cluster evaporation processes. We find that NGC 1513 migrated about 0.50 kpc from its birth place. [ABSTRACT FROM AUTHOR]

Objective: We make use of multiple data sources to examine whether there has been geographical polarization in the political behavior of Texas Hispanics from 2012 to 2022. It is widely known that partisan divisions in the American electorate continue to cleave along geographic lines. However, much of this literature on the urban–rural divide does not focus on a specific racial group, and if it does, then it typically highlights differences among non‐Hispanic white voters (Anglos). Methods: Making use of aggregate‐ and individual‐level data, we assess Texas Hispanics' party affiliation, participation, and vote choice according to geographic location. Results: We find notable evidence of geographic‐based partisan polarization among Texas' burgeoning Hispanic population. Conclusions: Although the movement of rural/small town Texas Hispanics toward the Republican Party from 2012 to 2022 pales in comparison to this shift among Texas Anglos, a similar partisan dynamic manifests among the former group. We abstain from using the word realignment to characterize these changes in Texas Hispanics' political behavior according to geographic location, but, nevertheless, it is clear that the Democratic Party's hold on this potentially pivotal group in the Lone Star State's electorate has loosened, and especially among rural/small town Latinos since the rise of Donald Trump. [ABSTRACT FROM AUTHOR]

We present a suite of binary evolution models with massive primaries (10 ≤ M 1 ≤ 40 M ⊙) and periods and mass ratios chosen such that the systems undergo nonconservative mass transfer while the primaries have helium cores. We track the total mass and chemical composition of the ejecta from these systems. This material shows the abundance signatures of hot hydrogen burning that are needed to explain the abundance patterns seen in multiple populations in massive star clusters. We then calculate the total yield of a population of binary stars with masses, mass ratios, and periods consistent with their distribution in a field population. We show that the overall abundance of this material is enriched in helium, nitrogen, sodium, and aluminum, and depleted in carbon, oxygen, and magnesium, by amounts that are consistent with observations. We also show that such a population of binaries will return approximately 25% of its mass in this ejecta (compared to 4% if all the stars were single), over a characteristic timescale of about 12 Myr. We argue that massive binaries must be seriously considered as a contributor to the source of enriched material needed to explain the multiple populations in massive clusters, since essentially all massive stars are formed in binaries or higher-order multiples, massive binaries are primarily formed in clusters, and massive binaries naturally produce material of the right composition. [ABSTRACT FROM AUTHOR]

We present the deepest J −Ks near-infrared photometry of the globular cluster M5 (NGC 5904) from observations taken with the Gemini South Adaptive Optics Imager in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-m Gemini South telescope. Point spread function (PSF) photometry was carried out using a spatially variable PSF, zero-point calibrations based on correlations to a standard photometric catalogue, colour corrections, and crowding corrections. The latter corrections provided a new challenge given the field variations of the adaptive optics corrections in the central crowded regions of this cluster. The final photometric precision in our J− Ks colour–magnitude diagram exposes a dispersion among the lower main-sequence stars of M5 for the first time. This dispersion occurs below a main-sequence knee due to variations in the helium and CNO (carbon, nitrogen, and oxygen) abundances from multiple stellar populations, consistent with results from the bright evolved stars in this cluster from ultraviolet to near-infrared Hubble Space Telescope photometry and ground-based spectroscopy. This paper completes our original GeMS quality analysis programme, providing insights into adaptive optics analyses in crowded fields. [ABSTRACT FROM AUTHOR]

The spatial–kinematic structure of 48 young star clusters and associations is investigated. Moran's I statistic is used to quantify the degree of kinematic substructure in each region, and the results are compared to those expected assuming the hierarchical or monolithic models of star cluster formation. Of the observed regions, 39 are found to have significant kinematic substructure, such that they are compatible with the hierarchical model and incompatible with the monolithic model. This includes multiple regions whose Q parameter shows the region to be centrally concentrated and clustered. The remaining nine are compatible with both models. From this, it is concluded that the kinematic substructure of the observed star clusters represents strong evidence in favour of the hierarchical model of star cluster formation over the monolithic model. [ABSTRACT FROM AUTHOR]

Rapid formation of supermassive black holes occurs in dense nuclear star clusters that are initially gas-dominated. Stellar-mass black hole remnants of the most massive cluster stars sink into the core, where a massive runaway black hole forms as a consequence of combined effects of repeated mergers and Eddington-limited gas accretion. The associated gravitational wave signals of high-redshift extreme mass-ratio inspirals are a unique signature of the nuclear star cluster scenario. [ABSTRACT FROM AUTHOR]

New boron abundances or upper limits have been determined for eight early B stars in the young Galactic open cluster NGC 3293, using UV spectra obtained by the Hubble Space Telescope Cosmic Origins Spectrograph. With previous observations, there are now 18 early B stars in this cluster with boron measurements. Six of the newly observed stars have projected rotational velocities greater than 200 km s−1, allowing new constraints on rotationally driven mixing in main-sequence stars. When comparing to synthetic model populations, we find that the majority of our sample stars agree well with the predicted trends of stronger boron depletion for larger rotation and for larger mass or luminosity. Based on those, a smaller than the canonical rotational mixing efficiency (f c ≈ 0.0165 versus the more standard value of 0.033) appears to be favored. In addition, the five mostly slowly rotating stars, when considered as a group, tend to show more boron depletion than expected from rotational mixing, and we speculate that most or all of these originate from binary mergers. [ABSTRACT FROM AUTHOR]

We recently introduced three new parameters that describe the shape of the normalized cumulative radial distribution (nCRD) of the innermost stars in globular clusters (GCs) and trace the clusters' dynamical evolution. Here, we extend our previous investigations to the case of a large set of Monte Carlo simulations of GCs, started from a broad range of initial conditions. All the models are analyzed at the same age of 13 Gyr when they have reached different evolutionary phases. The sample of models is well representative of the structural properties of the observed population of Galactic GCs. We confirm that the three nCRD parameters are powerful tools to distinguish systems in the early stages of dynamical evolution from those that have already experienced core collapse. They might also help disentangle clusters hosting a low-mass intermediate-mass black hole of a few hundred solar masses from cases with large concentrations of dark remnants in their centers. With respect to other dynamical indicators, the nCRD parameters offer the advantage of being fully empirical and easier to measure from observational data. [ABSTRACT FROM AUTHOR]

We present the results of direct-method metallicity measurements in the disc and outflow of the low-metallicity starburst galaxy NGC 1569. We use Keck Cosmic Web Imager observations to map the galaxy across 54″ (800 pc) along the major axis and 48″ (700 pc) along the minor axis with a spatial resolution of 1″ (∼15 pc). We detect common strong emission lines ([O  iii ] λ5007, H β, [O  ii ] λ3727) and the fainter [O  iii ] λ4363 auroral line, which allows us to measure electron temperature (Te) and metallicity. Theory suggests that outflows drive metals out of the disc driving observed trends between stellar mass and gas-phase metallicity. Our main result is that the metallicity in the outflow is similar to that of the disc, Z out/ Z ISM ≈ 1. This is consistent with previous absorption line studies in higher mass galaxies. Assumption of a mass-loading factor of |$\dot{M}_{\rm out}/{\rm SFR}\sim 3$| makes the metal-loading of NGC 1569 consistent with expectations derived from the mass–metallicity relationship. Our high spatial resolution metallicity maps reveal a region around a supermassive star cluster (SSC-B) with distinctly higher metallicity and higher electron density, compared to the disc. Given the known properties of SSC-B the higher metallicity and density of this region are likely the result of star formation-driven feedback acting on the local scale. Overall, our results are consistent with the picture in which metal-enriched winds pollute the circumgalactic medium surrounding galaxies, and thus connect the small-scale feedback processes to large-scale properties of galaxy haloes. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation on the mass function (MF) of a snake-like stellar structure in the solar neighbourhood, building on our previous discovery. To ensure the reliability of the data, we reselect the member stars of the Stellar 'Snake' in the latest Gaia Data Release 3 using the same approach as the initial series of articles. We also precisely measure the physical parameters of the clusters within the Stellar Snake. In light of the high completeness of the member stars in the cluster regions, we develop a simulated model colour–magnitude diagram-based inference method to derive the mass function, binary fraction, and mass-ratio distribution of the clusters in the Stellar Snake. Notably, despite their similar ages and metallicity, we discover systematic variations in the MFs along the elongation direction of the Snake in the mass range of 0.5 to 2.0 M⊙. The 'head' of the Snake conforms to a canonical initial mass function with a power-law slope of α ∼ −2.3. Extending towards the 'tail', the MF becomes more top-light, indicating a deficiency of massive stars within these clusters. This result provides evidence for the delayed formation of massive stars in the clusters. Such clues give support to the hypothesis that the Stellar Snake constitutes as a hierarchically primordial structure. [ABSTRACT FROM AUTHOR]

We report the discovery of 23 globular cluster (GC) candidates around the relatively isolated dwarf galaxy IC 2574 within the Messier 81 (M81) group, at a distance of 3.86 Mpc. We use observations from the HST Advanced Camera for Surveys (ACS) to analyse the imaging in the F814W and F555W broad-band filters. Our GC candidates have luminosities ranging from −5.9 ≥ MV ≥ −10.4 and half-light radii of 1.4 ≤ r h ≤ 11.5 pc. We find the total number of GCs (N GC) = 27 ± 5 after applying completeness corrections, which implies a specific frequency of S N = 4.0 ± 0.8, consistent with expectations based on its luminosity. The GC system appears to have a bimodal colour distribution, with 30 percent of the GC candidates having redder colours. We also find five objects with extremely blue colours that could be young star clusters linked to an intense star formation episode that occurred in IC 2574 ∼1 Gyr ago. We make an independent measurement of the halo mass of IC 2574 from its kinematic data, which is rare for low mass galaxies, and find log M 200 = 10.93 ± 0.08. We place the galaxy on the well-known GC system mass–halo mass relation and find that it agrees well with the observed near-linear relation. IC 2574 has a rich GC population for a dwarf galaxy, which includes an unusually bright ω Cen-like GC, making it an exciting nearby laboratory for probing the peculiar efficiency of forming massive GCs in dwarf galaxies. [ABSTRACT FROM AUTHOR]

We consider scenarios for non-thermal particle acceleration and re-acceleration in the central cores of compact massive star clusters, aided by insights from high-resolution hydrodynamic simulations. We show that (i) particles are unlikely to interact with many shocks during their lifetimes in the core; (ii) colliding flows do not produce hard spectra; and (iii) turbulent re-acceleration in the core is suppressed. Inefficient re-acceleration mechanisms are not expected to produce hard components nor to increase the maximum energy within the cores of massive star clusters. Models in which the observed ultra-high-energy gamma rays originate in the core of massive stellar clusters are thus disfavoured. [ABSTRACT FROM AUTHOR]

We provide an analytic review of problems of the modern stellar astronomy. It mostly based on talks presented at the thirteenth annual conference on Modern Stellar Astronomy, held in Volgograd State University (Russia) in May 2023. [ABSTRACT FROM AUTHOR]

In this paper, we use two methods, an algorithm of the density-based spatial clustering of applications with noise combined with the Gaussian mixture model, and the maximum likelihood method, to study two open clusters: IC 2488 and IC 2714 with Gaia Data Release 3 data. We compare the two methods in terms of cluster star number, isochrone fitting, cluster mass, and radius. The comparison shows that the selections of cluster stars by the two methods are consistent. The parameters obtained by the two methods are very close. But there are slight differences between the two methods for faint stars in IC 2714. The maximum likelihood method selects more faint stars outside of the main-sequence stripe. We conclude that the maximum likelihood method is more likely affected by field stars. [ABSTRACT FROM AUTHOR]