Aims. In this work, we exploit the most robust, old, and cosmology-independent age estimates of individual stars from Gaia DR3 to place a lower bound on the age of the Universe, t(U). These constraints can be used as an anchor point for any cosmological model, thus providing an upper limit to the Hubble constant H-0. Methods. Our primary stellar age catalog comprises 3000 of the oldest and most robustly measured main-sequence turn-off (MSTO) and subgiant branch (SGB) stars, with ages older than 12.5 Gyr and associated uncertainty below 1 Gyr. Stellar ages are derived via isochrone fitting using the Bayesian code StarHorse, spanning the uniform range 0-20 Gyr, not considering any cosmological prior knowledge on t(U). By applying a conservative cut in the Kiel diagram and strict quality cuts on both stellar parameters and posterior probability distribution shapes, and filtering out potential contaminants, we isolated a final sample of 160 bona fide stars, the most numerous sample of precise and reliable MSTO and SGB stars ages available to date. Results. The age distribution of the final sample peaks at 13.6 +/- 1.0 (stat) +/- 1.4 (syst) Gyr. Assuming a maximum formation redshift for these stars of z(f) = 20, corresponding to a formation delay of similar to 0.2 Gyr, we obtain a lower bound on t(U) of t(U) >= 13.8 +/- 1.0 (stat) +/- 1.4 (syst) Gyr. Considering the 10th percentile of the posterior probability distributions of the individual stars, we find that, at 90% confidence level, 70 stars favour t(U) > 13 Gyr, while none exceeds 14.1 Gyr. For this upper envelope to fall below 13 Gyr, a shift of nearly the full systematic error budget would be required, indicating that such low values are only attainable under very peculiar assumptions. Conclusions. This work presents the first statistically significant use of individual stellar ages as cosmic clocks, opening a new independent approach for cosmological studies. While this analysis already represents a significant step forward, future Gaia data releases will enable even larger and more precise stellar samples, further strengthening these constraints.

In this study we investigate the chemical enrichment of the rapid neutron-capture process in the Small Magellanic Cloud (SMC). We measured the [Eu/Fe] abundance ratio of 209 giant stars that are confirmed members of the SMC, providing the first extensive dataset of Eu abundances in this galaxy across its full metallicity range, spanning more than 1.5 dex. We compared the Eu abundances with those of Mg and Ba to evaluate the efficiency of the r-process relative to alpha-capture and s-process nucleosynthesis. The SMC shows enhanced [Eu/Fe] values at all metallicities (comparable with the values measured in the Milky Way) and a clear decline as [Fe/H] increases (from approximately -1.75 dex to approximately -0.5 dex), which is consistent with the onset of Type Ia supernovae. In contrast, [Eu/Mg] is enhanced by about +0.5 dex at all [Fe/H] and thus significantly above the values observed in Milky Way stars, where [Eu/Mg] remains close to the solar value, reflecting comparable production of r-process and alpha-capture elements. Moreover, [Ba/Eu] increases with metallicity beginning at [Fe/H] approximate to -1.5 dex, namely at a lower metallicity with respect to the Milky Way, where [Ba/Eu] starts to increase around [Fe/H] approximate to -1 dex. Our findings suggest the SMC has a higher production of Eu (with respect to the alpha-elements) than the Milky Way, but it is still in line with what has been observed in other dwarf systems within the Local Group. We confirm that galaxies with star formation efficiencies lower than the Milky Way have a high [Eu/alpha], probably indicating stronger efficiency of the delayed sources of the r-process at low metallicities.

We analyse high signal-to-noise ESPaDOnS/CFHT spectra of 20 very metal-poor (VMP) stars ([Fe/H] < -2.0) in the solar neighbourhood (within similar to 2 kpc), selected to be on planar orbits with maximum heights less than or similar to 4 kpc. The sample comprises 11 stars on prograde and 9 on retrograde orbits, all with relatively high eccentricities (0.5-0.9). Their chemical abundance patterns indicate enrichment from high-energy supernovae and hypernovae up to the Fe-peak, and contributions from fast-rotating massive stars and neutron star mergers for the neutron-capture elements. No significant chemical differences are found between prograde and retrograde stars. The [Sr, Ba, Eu/Fe] ratios resemble those of stars in classical dwarfs galaxies. Chemical dispersion and distance analyses further highlight the internal similarity of the sample and its separation from the bulk of the observed, non-planar halo population. Applying the same kinematical selection to another homogeneous dataset yields consistent results, confirming that this group of planar VMP stars exhibit peculiar chemical properties distinct from those of the observed halo and other known Galactic structures. These findings suggest that the stars formed in an environment that experienced a homogeneous chemical evolution akin to that of dwarf galaxies. A plausible scenario, supported by cosmological zoom-in simulations, is the early accretion of a single system whose subsequent dynamical evolution naturally produced stars on both prograde and retrograde planar orbits. If this interpretation is correct, we tentatively refer to this putative progenitor as Loki. However, comparisons with other planar VMP stars spanning a wider range of chemo-dynamical properties indicate that multiple accretion events likely contributed to this diverse population orbiting close to the Galactic plane.

Globular clusters encode the hierarchical assembly history of the Milky Way and the physics of multiple stellar populations. Using homogeneous stellar parameters for 69 Galactic globular clusters derived while modelling multiple populations, we reconstruct progenitor-specific age–metallicity relations (AMRs) and test whether helium-related multiple-population (MP) properties depend on progenitor origin once cluster mass and metallicity are controlled for. Ages, helium spreads (δY), mean helium abundances (Y̅), and first-population fractions (f_ P1) are drawn from hierarchical Bayesian CMD modelling. Progenitor families are identified via chemo-dynamical clustering, AMRs reconstructed within a hierarchical Bayesian framework, and MP indicators tested for environmental dependence. Enrichment timescales are consistent with τ≲ 2 Gyr, though individual progenitors prefer shorter values when fitted independently. The primary distinction is the extent of chemical evolution: most systems reach Δ[Fe/H] ∼ 1.1–1.3 dex while Sagittarius achieves ∼1.6 dex and higher terminal metallicities. Gaia–Sausage–Enceladus and low-energy/Kraken are the dominant accretion events. Neither δY nor Y̅ depends on progenitor origin; the mass–MP scaling is indistinguishable across in-situ and accreted systems. Sequoia clusters alone show higher f_ P1 at fixed mass and metallicity. AMRs carry fossil signatures of progenitor chemical evolution and mass hierarchy. Helium enrichment amplitude is regulated by cluster mass and blind to environment, pointing to universal cluster-scale formation physics, with the sole exception of a residual dependence in f_ P1, suggesting the enriched-star fraction retains a secondary environmental imprint.

Classical Cepheids (CCs) have long been considered excellent tracers of the chemical evolution of the Milky Way's young disk. We present a homogeneous, non-local thermodynamical equilibrium (NLTE) spectroscopic analysis of 401 Galactic CCs, based on 1351 high-resolution optical spectra, spanning Galactocentric distances from 4.6 to 29.3 kpc. Using PySME with MARCS atmospheres and state-of-the-art grids of NLTE departure coefficients, we derived the atmospheric parameters and abundances for key species tracing multiple nucleosynthetic channels (O, Na, Mg, Al, Si, S, Ca, Ti, Mn, Fe, and Cu). Our sample is the largest CC NLTE dataset to date and it achieves high internal precision, enabling the robust modelling of present-day thin-disk abundance patterns and radial gradients. We estimate abundance gradients using three analytic prescriptions (linear, logarithmic, bilinear with a break) within a Bayesian, outlier-robust framework. We also applied Gaussian process (GP) regression to capture non-parametric variations. We find that NLTE atmospheric parameters differ systematically from LTE determinations. Moreover, iron and most elemental abundance profiles are better described by non-linear behaviour rather than by single-slope linear models: logarithmic fits generally outperform simple linear models, while bilinear fits yield inconsistent break radii across elements. GP models reveal a consistent outer-disk flattening of [X/H] for nearly all studied elements. The [X/Fe] ratios are largely flat with Galactocentric radius, indicating coherent chemical scaling with iron across the thin disk, with modest positive offsets for Na and Al and mild declines for Mn and Cu. Finally, Cepheid kinematics confirm thin-disk orbits for the great majority of the sample. Comparisons with recent literature shows an overall agreement, while also highlighting NLTE-driven differences, especially in outer-disk abundances. These results provide tighter empirical constraints for chemo-dynamical models of the Milky Way and set the stage for future NLTE mapping with upcoming large spectroscopic surveys.

We present the chemical abundances of Fe, alpha-, and neutron-capture elements in 12 metal-poor Small Magellanic Cloud (SMC) giant stars, observed with the high-resolution spectrographs UVES/VLT and MIKE/Magellan. These stars are characterised by [Fe/H] between -2.3 and -1.4 dex, with ten of them with [Fe/H] < -1.8 dex. According to theoretical age-metallicity relations for this galaxy, these stars were formed in the first Gyr of life of the SMC and represent the oldest SMC stars known so far. The [alpha/Fe] abundance ratios are enhanced but at a lower level than MW metal-poor stars, as expected according to the slow star formation rate (SFR) of the SMC. The sample exhibits a large star-to-star scatter in all the neutron-capture elements. The two r-process elements measured in this work (Eu and Sm) have abundance ratios from solar up to +1 dex, three of them with [Eu/Fe] > +0.7 dex and labelled as r-II stars. This [r/Fe] distribution indicates that the r-process in the SMC can be extremely efficient but is still largely affected by the stochastic nature of the main sites of production and the inefficient gas mixing in the early SMC evolution. A similar scatter is observable also for the s-process elements (Y, Ba, La, Ce, and Nd), with the stars richest in Eu also being rich in these s-elements. Also, all the stars exhibit sub-solar [s/Eu] abundance ratios. At the metallicities of these stars, the production of neutron-capture elements is driven by the r-process because the low-mass AGB stars have not yet evolved and left their s-process signature in the interstellar medium (ISM). In this work, we also present a set of stochastic chemical evolution models tailored for the SMC to validate this scenario.

We revisit the determination of the age of the Universe from galactic globular clusters, extending previous analyses by explicitly accounting for the presence of multiple stellar populations within each cluster. Using high–quality Hubble Space Telescope color–magnitude diagrams for 69 globular clusters, we relax the standard single–population assumption, and model two stellar populations with independent ages, metallicities, helium abundances, and population fractions. The inference is performed using the full color–magnitude diagram morphology, an explicit treatment of field contamination, and a hierarchical framework that propagates non–Gaussian age posteriors. Allowing for multiple stellar populations has a negligible impact on globular cluster age estimates. The ages of the oldest populations remain fully consistent with those obtained under the single–population assumption, with differences at the 0.6σ level. Restricting to the metal–poor subsample ([Fe/H] < -1.5), we infer a dominant old component with mean age t_ GC=13.61±0.25 (stat) ±0.23 (sys) Gyr. Adopting a conservative delay between the Big Bang and the formation of the first globular clusters, we obtain an age of the Universe of t_ U=13.81±0.25 (stat) ±0.23 (sys) Gyr. In addition to age constraints, our analysis yields simultaneous measurements of metallicity and helium content for the different populations, including constraints on helium enrichment and population fractions which are consistent with independent determinations from the literature. These results demonstrate that globular–cluster–based cosmic chronometry is robust to stellar population complexity, reinforcing its role as a precise and largely cosmological model–independent probe of the age of the Universe.

Stellar streams, remnants of compact star systems stretched out by the tidal forces of the Milky Way, offer a unique way to study stellar populations that formed billions of years ago. A particularly unique stream is C-19, the most metal-poor stellar stream known at less than a thousandth of the Sun's metallicity. The nature of C-19 is not yet clear, with properties that resemble both star clusters and ultra faint dwarf galaxies, yet in either case its extremely low metallicity indicates very early star formation, <1 Gyr after the Big Bang. Here, we present the first detailed study on the nature of C-19 based on the chemical abundances of 14 member stars from high-resolution spectroscopy. These reveal that C-19 formed stars in an early, rapid, and prolific star formation event, with mild inhomogeneous mixing of elements produced in massive stars. There is otherwise no evidence for subsequent star formation, multiple stellar populations, nor chemical evolution. Although C-19 is currently disrupted in the Milky Way halo, it offers a rare and complementary window into the details of star formation and chemical evolution in the early universe, ideal for comparisons with current studies of primordial star formation in the high-redshift universe.

Over the past decade, stellar rotation has emerged as a key factor in shaping the morphology of color-magnitude diagrams of young and intermediate-age star clusters. In this study, we use MUSE integral-field spectroscopy to investigate the stellar rotation of 2300 stars in the 1.5 Gyr old cluster NGC 1783 in the Large Magellanic Cloud. The effective temperature, surface gravity, radial velocity, and projected rotational velocity (vsini) of the entire sample were obtained within a Bayesian framework to derive robust estimates of these parameters along with their associated errors. The analysis shows that stars along the extended main sequence turn-off (eMSTO) cover a wide range of rotational velocities, from values consistent with no or slow rotation up to vsini similar to 250 km s(-1). The distribution of stellar rotation velocities appears to play a crucial role in explaining the broadening of the eMSTO in this cluster, and a correlation is observed between vsini and the color of the eMSTO stars, with vsini increasing as the color becomes redder. Among the eMSTO stars, we investigate the peculiar population of stars strongly dimmed in the UV (so-called UV-dim stars), recently discovered in NGC 1783. UV-dim stars show clear photometric evidence of self-extinction and mild spectroscopic signatures typically observed in shell stars, suggesting that they have likely a decretion disk observed nearly equator-on. Interestingly, the study also shows that a significant fraction of UV-dim stars are slow rotators. We discuss potential implications these results may have on our understanding of the formation and evolution of UV-dim stars and we propose that the rotational properties of the UV-dim stars should vary with cluster age.

Aims. In this work, we explore the reliability and robustness in measuring the ages and main physical properties of a sample of old Milky Way globular clusters (GCs) from their integrated light. This approach sets the stage for using GCs as cosmic clocks at high redshift. Additionally, it enables us to establish an independent lower limit on the age of the Universe, and an upper limit on H0. Methods. We analysed a sample of 77 GCs from the WAGGS project, by first measuring their spectral features (Lick indices and spectroscopic breaks) with PyLick and then performing full spectral fitting with BAGPIPES. The analysis of Lick indices offers an initial estimate of the population's age and metallicity, generally aligning well with values reported in the literature. However, it also highlights a subset of old clusters for which we estimate younger ages. This discrepancy is primarily attributed to the presence of horizontal branches (HBs) with complex morphologies, which are not accounted for in the stellar population models. With full spectral fitting we measured the GCs' ages, metallicities, and masses, testing how removing the cosmological prior on the ages affects the final results. Results. Compared to isochrone fitting estimates, ages are best recovered when the cosmological prior is removed, with a 20% increase in the number of GCs showing ages compatible with literature values within +/- 1.5 Gyr. The derived metallicity and mass are consistently in good agreement with the reference values, regardless of HB morphology, [Z/H], or the fit settings. The average discrepancies across the entire sample are = -0.02 +/- 0.24 dex for metallicity and = 0.04 +/- 0.28 dex for mass. Metal-rich GCs ([Z/H] >= -0.4) showing a red HB (with morphological parameter HBR > 0) are the sub-group in which ages are best recovered. In this group, 70% of the results align with literature values within +/- 1.5 Gyr. Identifying the tail of the oldest cosmology-independent ages with a Gaussian mixture model, we obtained a sample of 24 objects with < age > = 13.4 +/- 1.1 Gyr. Conclusions. Being a natural lower limit on the age of the Universe, we used the age of the oldest GCs to constrain the Hubble constant, obtaining H0 = 70.5-6.3+7.7 km s-1 Mpc-1 H 0 = 70 . 5 - 6.3 + 7.7 km s - 1 Mpc - 1 $ H_0 = 70.5<^>{+7.7}_{-6.3}\, \mathrm{km\,s<^>{-1}\,Mpc<^>{-1}} $ (stat+syst) when a flat Lambda CDM with Omega m = 0.30 +/- 0.02 (based on low-z measurements) was assumed. Validating the analysis of GCs based on their integrated light lays the foundation for extending this type of study to high redshift, where GCs have begun to appear in lensed fields, thanks to JWST.

Relics of ancient accretion events experienced by the Milky Way are predominantly located within the stellar halo of our Galaxy. However, debris from different objects display overlapping distributions in dynamical spaces, making it extremely challenging to properly disentangle their contribution to the build-up of the Galaxy. To shed light on this chaotic context, we initiated a program aimed at the homogeneous chemical tagging of the local halo of the Milky Way, focusing on the component in retrograde motion, since this is expected to host a large fraction of stars accreted from past mergers. The A Walk on the Retrograde Side (WRS) project targets retrograde halo stars in the solar neighborhood with accurate 6D phase space information available, measuring the precise chemical abundance of several chemical elements from high-resolution spectroscopy. In this first paper, we present the project and the analysis of high-resolution spectra obtained with UVES at VLT and at LBT for 186 stars. We obtained accurate radial velocity and chemical abundances for several elements for all the target stars. In particular, we focus on the chemical composition of a specific subset of substructures that have been dynamically identified in the literature. Our study reveals that two among the more recently discovered structures in the retrograde halo, namely, Antaeus/L-RL64 and ED-3, have identical chemical patterns and similar integrals of motion, suggesting a common origin. In turn, the abundance patterns of this unified system differ from that of Gaia-Enceladus, confirming that it is an independent structure. Finally, Sequoia exhibits a different chemistry with respect to that of Gaia-Enceladus at [Fe/H] < −1.5 dex, showcasing an excess of stars with lower Mg and Ca in the common metallicity range.

We used the spectro-photometric information of similar to 219 million stars from Gaia's Data Release 3 (DR3) to calculate synthetic, narrowband, metallicity-sensitive CaHK magnitudes that mimic the observations of the Pristine survey, a survey of photometric metallicities of Milky Way stars that has been mapping more than 6500 deg(2) of the northern sky with the Canada-France-Hawaii Telescope since 2015. These synthetic magnitudes were used for an absolute recalibration of the deeper Pristine photometry and, combined with broadband Gaia information, synthetic and Pristine CaHK magnitudes were used to estimate photometric metallicities over the whole sky. The resulting metallicity catalogue is accurate down to [Fe/H]similar to-3.5 and is particularly suited for the exploration of the metalpoor Milky Way ([Fe/H] < -1.0). We make available here the catalogue of synthetic CaHKsyn magnitudes for all stars with BP/RP information in Gaia DR3, as well as an associated catalogue of more than similar to 30 million photometric metallicities for high signal-to-noise FGK stars. This paper further provides the first public data release of the Pristine catalogue in the form of higher quality recalibrated Pristine CaHK magnitudes and photometric metallicities for all stars in common with the BP/RP spectro-photometric information in Gaia DR3. We demonstrate that, when available, the much deeper Pristine data greatly enhance the quality of the derived metallicities, in particular at the faint end of the catalogue (G(BP) greater than or similar to 16). Combined, both photometric metallicity catalogues include more than two million metal-poor star candidates ([Fe/H](phot) < -1.0) as well as more than 200 000 and similar to 8000 very and extremely metal-poor candidates ([Fe/H](phot) < -2.0 and < -3.0, respectively). Finally, we show that these metallicity catalogues can be used efficiently, among other applications, for Galactic archaeology, to hunt for the most metal-poor stars, and to study how the structure of the Milky Way varies with metallicity, from the flat distribution of disk stars to the spheroid-shaped metal-poor halo.

In this study, we report the results of Fe, Mg, Al, and Si abundances analysis for a sample of 439 stars in Omega Centauri, using high-resolution spectra obtained with the VLT/FLAMES multi-object spectrograph. Our analysis reveals the presence of four distinct Fe populations, with the main peak occurring at low metallicity, consistent with previous literature findings. We observe a discrete and pronounced Mg-Al anti-correlation, which exhibits variations in shape and extension as a function of metallicity. Specifically, this anti-correlation is present in stars with metallicities lower than approximately -1.3 dex, while it becomes less evident or absent for higher [Fe/H] values. Additionally, we detect (anti-) correlations between Mg and Si, and between Al and Si, whose extensions also vary with metallicity, similar to the Mg-Al anti-correlation. These results suggest that the MgAl cycle plays a crucial role in the formation of multiple populations in Omega Centauri, with the presence of all (anti-) correlations at metallicities lower than -1.3 dex providing evidence for the burning of Mg at very high temperatures (> 10^8 K), at least in the metal-poor regime. Furthermore, we observe a clear trend of stars with [Al/Fe] > +0.5 dex as a function of metallicity, confirming for the first time the existence of the two channels of Al production and destruction. This evidence can help to provide further constraints on the potential nature of the polluters responsible for the observed chemical anomalies in this stellar system. Finally, we find that the two most metal-poor populations identified in our sample are compatible with null or very small metallicity dispersion and we discuss how this result fit into a scenario where Omega Centauri is the remnant of a disrupted nucleated dwarf galaxy.

We present our analysis of VLT/UVES and X-shooter observations of six very metal-poor stars, including four stars at [Fe/H] ≈ −3 in the Fornax and Carina dwarf spheroidal (dSph) galaxies. To date, this metallicity range in these two galaxies has not yet been investigated fully, or at all in some cases. The chemical abundances of 25 elements are presented, based on 1D and local thermodynamic equilibrium (LTE) model atmospheres. We discuss the different elemental groups, and find thatα- and iron-peak elements in these two systems are generally in good agreement with the Milky Way halo at the same metallicity. Our analysis reveals that none of the six stars we studied exhibits carbon enhancement, which is noteworthy given the prevalence of carbon-enhanced metal-poor stars withouts-process enhancement (CEMP-no) in the Galaxy at similarly low metallicities. Our compilation of literature data shows that the fraction of CEMP-no stars in dSph galaxies is significantly lower than in the Milky Way, and than in ultra-faint dwarf galaxies. Furthermore, we report the discovery of the lowest metallicity, [Fe/H] = −2.92,r-process rich (r-I) star in a dSph galaxy. This star, fnx_06_019, has [Eu/Fe] = +0.8, and also shows enhancement of La, Nd, and Dy, [X/Fe] > +0.5. Our new data in Carina and Fornax help populate the extremely low metallicity range in dSph galaxies, and add to the evidence of a low fraction of CEMP-no stars in these systems.

Relics of ancient accretion events experienced by the Milky Way are predominantly located within the stellar halo of our Galaxy. However, debris from different objects display overlapping distributions in dynamical spaces, making it extremely challenging to properly disentangle their contribution to the build-up of the Galaxy. To shed light on this chaotic context, we initiated a program aimed at the homogeneous chemical tagging of the local halo of the Milky Way, focusing on the component in retrograde motion, since this is expected to host a large fraction of stars accreted from past mergers. The A Walk on the Retrograde Side (WRS) project targets retrograde halo stars in the solar neighborhood with accurate 6D phase space information available, measuring the precise chemical abundance of several chemical elements from high-resolution spectroscopy. In this first paper, we present the project and the analysis of high-resolution spectra obtained with UVES at VLT and at LBT for 186 stars. We obtained accurate radial velocity and chemical abundances for several elements for all the target stars. In particular, we focus on the chemical composition of a specific subset of substructures that have been dynamically identified in the literature. Our study reveals that two among the more recently discovered structures in the retrograde halo, namely, Antaeus/L-RL64 and ED-3, have identical chemical patterns and similar integrals of motion, suggesting a common origin. In turn, the abundance patterns of this unified system differ from that of Gaia-Enceladus, confirming that it is an independent structure. Finally, Sequoia exhibits a different chemistry with respect to that of Gaia-Enceladus at [Fe/H] < -1.5 dex, showcasing an excess of stars with lower Mg and Ca in the common metallicity range.

The Gaia Collaboration has recently reported the detection of a 33 M$_\odot$ black hole in a wide binary system located in the Solar neighbourhood. Here we explore the relationship between this black hole, known as Gaia BH3, and the nearby ED-2 halo stellar stream. We study the orbital characteristics of the Gaia BH3 binary and present measurements of the chemical abundances of ED-2 member stars derived from high-resolution spectra obtained with the VLT. We find that the Galactic orbit of the Gaia BH3 system and its metallicity are entirely consistent with being part of the ED-2 stream. The characteristics of the stream, particularly its negligible spread in metallicity and in other chemical elements as well as its single stellar population, suggest that it originated from a disrupted star cluster of low mass. Its age is comparable to that of the globular cluster M92 that has been estimated to be as old as the Universe. This is the first black hole unambiguously associated with a disrupted star cluster. We infer a plausible mass range for the cluster to be relatively narrow, between $2\times 10^3M_\odot$ and $4.2\times 10^4M_\odot$. This implies that the black hole could have formed directly from the collapse of a massive very-metal-poor star, but that the alternative scenario of binary interactions inside the cluster environment also deserves to be explored.

The Extremely Large Telescopes (ELTs), thanks to their large apertures and cutting-edge Multi-Conjugate Adaptive Optics (MCAO) systems, promise to deliver sharper and deeper data even than the JWST. SHARP is a concept study for a near-IR (0.95-2.45 mu m) spectrograph conceived to fully exploit the collecting area and the angular resolution of the upcoming generation of ELTs. In particular, SHARP is designed for the 2nd port of MORFEO@ELT. Composed of a Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER, MORFEO-SHARP will deliver high angular (similar to 30 mas) and spectral (R?300, 2000, 6000, 17000) resolution, outperforming NIRSpec@JWST (100 mas). SHARP will enable studies of the nearby Universe and the early Universe in unprecedented detail. NEXUS is fed by a configurable slit system deploying up to 30 slits with similar to 2.4" length and adjustable width, over a field of about 1.2'x1.2' (35 mas/pix). Each slit is fed by an inversion prism able to rotate by an arbitrary angle the field that can be seen by the slit. VESPER is composed of 12 probes of 1.7"x1.5" each (spaxel 31 mas) probing a field 24"x70". SHARP is conceived to exploit the ELT aperture reaching the faintest flux and the sharpest angular resolution by joining the sensitivity of NEXUS and the high spatial sampling of VESPER to MORFEO capabilities. This article provides an overview of the scientific design drivers, their solutions, and the resulting optical design of the instrument achieving the required optical performance.

Photometric investigations have revealed that Galactic globular clusters exhibit internal metallicity variations amongst the so-called first-population stars, until now considered to have a homogeneous initial chemical composition. This is not fully supported by the sparse spectroscopic evidence, which so far gives conflicting results. Here, we present a high-resolution re-analysis of five stars in the Galactic globular cluster NGC 2808 taken from the literature. Target stars are bright red giants with nearly identical atmospheric parameters belonging to the first population according to their identification in the chromosome map of the cluster, and we have measured precise differential abundances for Fe, Si, Ca, Ti, and Ni to the 0.03 dex level. Thanks to the very small uncertainties associated to the differential atmospheric parameters and abundance measurements, we find that target stars span a range of iron abundance equal to 0.25 +/- 0.06 dex. The individual elemental abundances are highly correlated with the position of the star along the extended sequence described by first population objects in the cluster chromosome map: bluer stars have a lower iron content. This agrees with inferences from the photometric analysis. The differential abundances for all other elements also show statistically significant ranges that point to intrinsic abundance spreads. The Si, Ca, Ti, and Ni variations are highly correlated with iron variations and the total abundance spreads for all elements are consistent within the error bars. This suggests a scenario in which short-lived massive stars exploding as supernovae contributed to the self-enrichment of the gas in the natal cloud while star formation was still ongoing.

The Small Magellanic Cloud (SMC) is the host of a rich system of globular clusters (GCs) that span a wide age range. The chemical composition of the SMC clusters is still poorly understood, despite their significance to chemical evolution studies. Here, we provide the first detailed chemical study of evolved giants in three distinct clusters, NGC 121 (10.5 Gyr), NGC 339 (6 Gyr), and NGC 419 (1.4 Gyr). Results are based on high-resolution spectra obtained with FLAMES at the Very Large Telescope. The chemical fingerprints of these clusters closely resemble those of SMC field stars, supporting the SMC's specific history of chemical enrichment relative to the Milky Way. The approximately solar-scaled [alpha/Fe] observed in all three clusters, independent of their [Fe/H], demonstrate the SMC's low star formation efficiency. Compared to their Milky Way counterparts, elements primarily produced by massive stars are severely underrepresented. Particularly, the young cluster NGC 419's extremely low [Zn/Fe] shows that hypernovae have contributed relatively little during the past two Gyr. The three GCs have high [Eu/Fe] values regardless of their age. This suggests that the production of the r-process elements in the SMC was extremely efficient up to 1.5 Gyr ago, with an enrichment timescale comparable to that from Type Ia supernovae. When the properties of the oldest SMC object NGC 121 are compared to those of in-situ Milky Way clusters and accreted clusters linked to the Gaia-Enceladus merger event, it is shown that the SMC had already attained the same metallicity as Gaia-Enceladus but with lower [Fe/H] ratios at the age of NGC 121. This suggests that the chemical enrichment histories of the early SMC and Gaia-Enceladus differed, and that the SMC probably had a lower mass in its early ages than Gaia-Enceladus.

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H]<-2.0) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457 and P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H]<-3.0) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]similar to-2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.