Ricardo Carrera

Context. Open clusters serve as key laboratories for studying the chemical evolution of the Milky Way. In particular, leveraging these coeval groups of stars to study elements beyond the iron peak provides insights into heavy-element nucleosynthesis, whose origins remain uncertain. Aims. This work aims to determine the Mo, Ru, and Zr abundances for 81 stars across 30 open clusters. We compare these new chemical patterns with those of key reference elements (Y, Sr, and Eu), which were previously derived by our group. This comparison seeks to disentangle the distinct contributions from various nucleosynthetic processes. Methods. Using the high-resolution spectra acquired within the Stellar Population Astrophysics programme using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo, we estimated chemical abundances through spectral synthesis with TSFitPy under local thermodynamic equilibrium (LTE) conditions. Results. This study provides the first Ru abundances for a large open cluster sample, alongside new measurements for Mo and Zr. We observe tight correlations between Mo, Ru, and other s -process elements (Sr, Y, and Zr), with slopes near unity, suggesting common enrichment timescales. Conversely, relations with the r -process element Eu show significant deviations, implying additional nucleosynthetic contributions. Crucially, chemical planes involving [Mo/Ru] and [s/Mo] ratios suggest systematic offsets when compared to theoretical s -process predictions.

Context . The recent discovery of filamentary stellar structures in the Milky Way disk raises the question of their formation in the context of the Galaxy evolution. Aims . In this work, we aim to kinematically and chemically characterize several filamentary stellar structures by looking for clues about their origin and formation mechanism. Methods . Recent works using machine-learning techniques and Gaia data have identified many previously unknown Galactic strings. We cross-matched such data with the kinematics derived from the most recent Gaia DR3 catalog as well as chemical data provided by the Galactic Archaeology with HERMES (GALAH) survey. Results . We found that most strings contain one or more open clusters and are kinematically hotter than open clusters (with internal velocity dispersions in the 1–7 km s ⁻¹ range) but cooler than field stars. 18 objects appear chemically homogeneous ( σ [ Fe/H ]≤0.1 dex), while two strings have a broad [Fe/H] distribution similar to the field stars but exhibit a different mean metallicity, which may identify them as migrating stellar structures. For seven objects the GALAH observations focus on the embedded open clusters; therefore, the chemical abundances are not representative of the whole structure. An object shows clues of chemical gradients along its extension in Galactic longitude. Conclusions . These objects may be evaporating or disrupted open clusters in which the chemical homogeneity is preserved in an unbound and expanding cloud of stars or co-moving stars belonging to a former and now disrupting star formation hub. In a few cases they appear to be moving groups with no chemical homogeneity, likely formed by the dynamical action of the Galactic bar or spiral arms. More data are needed to confirm such hypotheses.

Context . Open clusters are excellent tracers of the Galactic thin disk, providing insights into its formation and evolution. Precise cluster age determination is essential for studying cluster evolution as well as the evolution of the disk as a whole. Aims . With this work, our aim was to produce an updated catalog of cluster parameters (age, extinction, distance) by constraining cluster ages via newly available spectroscopic measurements of metallicity. Methods . Using high-quality astrometry from Gaia Data Release 3, we derived new cluster memberships via a machine learning-based clustering algorithm (AstroLink). We compiled metallicity measurements from multiple ground-based spectroscopic surveys (Gaia-ESO, GALAH DR3, APOGEE-OCCAM) and Gaia GSP-Spec into a uniform scale. The ages of 320 clusters were determined using a machine learning-accelerated approximate Bayesian isochrone-fitting code (based on ASteCA), adopting a multiband approach that incorporates Gaia XP and synthetic photometry. Results . This work resulted in a robust sample of open clusters with precisely determined parameters and uncertainties. In addition, this catalog may provide a foundation for machine learning models to infer parameters for a larger sample of objects without spectroscopic data, which is to be explored in future work.

Context . Of the thousands of newly discovered open clusters (OCs) thanks to the exquisite precision of the Gaia mission data, only a small fraction has been observed with high-resolution spectroscopy. Particularly, the population of OCs in the inner disc at relatively high altitudes ( Z ) from the Galactic plane remains poorly studied. Few such high-| Z | inner-disc OCs have been detected, and most are sparse groupings of stars that still await confirmation as real OCs. Aims . We performed a detailed spectroscopic analysis of the high-| Z | inner-disc OC UBC 1052, an old cluster located at a cylindrical Galactocentric radius R _GC = 6.1 kpc, where it is one of a few OCs situated at a considerable altitude ( Z = 340 pc). Methods . We used FLAMES/VLT to acquire high signal-to-noise ratio UVES spectra of four red clump (RC) members ( G ∼ 14 mag), from which we derived high-precision radial velocities and local thermodynamic equilibrium chemical abundances for 23 elements. A strict line-by-line differential analysis was carried out using a reference RC star and a solar analogue in the OC M 67, allowing us to derive very precise abundances for each star (a median precision in [X/H] of ≃0.06 dex). We also acquired GIRAFFE spectra for other candidate member stars and derived their radial velocities. Results . We determine that UBC 1052 has an age of 2.25 ± 0.25 Gyr, a distance of 3.11 ± 0.07 kpc, an extinction of A _V = 1.23 mag, and a mean radial velocity of v . We find that the four RC stars have fully compatible chemical abundances, thus confirming UBC 1052 as a real OC. It has [Fe/H] = +0.05 ± 0.01 dex, and with [X/H] dispersions among the four stars < 0.03 dex for 20 elements, we give conservative limits for chemical inhomogeneities at ≃0.05 dex for these species. Conclusions . UBC 1052 stands out as the oldest and highest-| Z | inner-disc OC studied at high resolution to date, being located in the poorly sampled inner Galactic region where old OCs and OCs with large maximum excursions from the plane are scarce. Its relatively low [Fe/H] at its R _GC suggests it is a rare candidate for an inward-migrated OC in the inner disc. Its detailed abundance pattern (e.g. [Ba/Zr] and [Nd/Y]) shows some interesting features that appear to be unique in the current census of OCs studied at high resolution, making it an interesting object for potential strong chemical-tagging searches for already dispersed member stars.

NGC 2509 is a distant (≈2.5 kpc) and little-studied open cluster located in the third Galactic quadrant. It is a moderately old cluster, whose age has not yet been precisely determined. The main-sequence stars in NGC 2509 follow a narrow distribution in the colormagnitude diagram, unlike other clusters of similar age. In addition, its chemical composition has never been investigated. To address these issues and characterize the cluster we performed moderate- and high-resolution spectroscopy with FLAMES@VLT of 132 stars, both dwarfs and giants, which represents a significant fraction (≈73%) of likely members. We provide atmospheric stellar parameters and, for the first time, chemical abundances for 21 species with atomic numbers up to 60. In our analysis we followed two different methodologies, both of which will be used for the incoming WEAVE stellar surveys. We find an average radial velocity for NGC 2509 of 58.6±1.3km s ⁻¹ and a mild supersolar metallicity ([Fe/H]≈0.1 dex). This value is slightly higher than expected according to its galactocentric distance, but still compatible with the Galactic gradient. From the lithium content of the dwarfs and the isochrone-fitting method we obtain an age for NGC 2509 of 1.26±0.3Gyr. The reddening across the cluster field is negligible ( A _V = 0.25 ± 0.02 mag). The cluster peculiar main sequence turnoff is due to a narrow distribution of the rotational velocities peaking at v sin i ≈ 80 km s ⁻¹ , with little dispersion. The chemical pattern of NGC 2509 follows the Galactic trends shown by other open clusters in the Galactic thin disk.

Context . Accurate determination of the chemical abundances in stars plays a pivotal role in understanding stellar structure and evolution, nucleosynthesis, and the chemical enrichment history of the Milky Way. Benchmark stars with precise and accurate atmospheric parameters and abundances are indispensable for calibrating spectroscopic surveys and testing stellar atmosphere models. Aims . This study focuses on the compilation of high-quality spectra and the determination of chemical abundances of iron-peak and α elements for the third version of the Gaia FGK benchmark stars (GBSv3). Methods . We compiled spectra of the GBSv3 from public archives and complemented these with our observations. We used fundamental atmospheric parameters to perform a spectroscopic analysis using the public code iSpec and derived the chemical abundances. Results . We compiled a homogeneous spectral library of high-resolution (42 000) and high signal-to-noise (>100) normalised spectra for 202 stars, including the 192 GBSv3, nine stars with indirect measurement of the angular diameter from previous Gaia FGK benchmark versions, and the Sun. Using four radiative transfer codes, we derived chemical abundances of 13 chemical species (Fe I, Fe II, Mg I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I). We performed an in-depth study of several sources of error. Conclusions . The GBSv3 contributes to the legacy samples of spectroscopic reference stars through improved statistics and homogeneity. This work offers the community a homogeneous spectral library and robust reference abundances for iron-peak and α elements, supported by an extensive analysis of the associated uncertainties.

Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE's operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of approximately 6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE's capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.

Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE’s operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of ∼6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE’s capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.

We use spectroscopic data for ∼6, 000 Red Giant Branch (RGB) stars in the Small Magellanic Cloud (SMC), together with proper motion data from Gaia Early Data Release 3 (EDR3), to build a mass model of the SMC. We test our Jeans mass modelling method (binulator + GravSphere) on mock data for an SMC-like dwarf undergoing severe tidal disruption, showing that we are able to successfully remove tidally unbound interlopers, recovering the dark matter density and stellar velocity anisotropy profiles within our 95% confidence intervals. We then apply our method to real SMC data, finding that the stars of the cleaned sample are isotropic at all radii (at 95% confidence) and that the inner dark matter density profile is dense, |$\rho _{\rm DM}(150\, {\rm pc}) = 1.58_{-0.58}^{+0.80}\times 10^8 M_{\odot } \rm kpc^{-3}$|⁠, consistent with a Λ Cold Dark Matter (ΛCDM) cusp. Our model gives a new estimate of the SMC’s total mass within 3 kpc (M_tot ≤ 3 kpc) of 2.29 ± 0.46 × 10⁹M_⊙. We also derive an astrophysical “J-factor” of 18.99 ± 0.16 GeV² cm⁻⁵ and a “D-factor” of 18.73 ± 0.04 GeV² cm⁻⁵, making the SMC a promising target for dark matter annihilation and decay searches. Finally, we combine our findings with literature measurements to test models in which dark matter is “heated up” by baryonic effects. We find good qualitative agreement with the Di Cintio et al. 2014 model but we deviate from the Lazar et al. 2020 model at high M_*/M₂₀₀ > 10⁻². We provide a new, analytic, density profile that reproduces dark matter heating behaviour over the range 10⁻⁴ < M_*/M₂₀₀ < 10⁻¹.

Context. Open clusters provide valuable information on stellar nucleosynthesis and the chemical evolution of the Galactic disk, as their age and distances can be measured more precisely with photometry than in the case of field stars. Aims. Our aim is to study the chemical distribution of the Galactic disk using open clusters by analyzing the existence of gradients with Galactocentric distance, azimuth, or height from the plane and dependency with age. Methods. We used the high-resolution spectra (R > 60 000) of 194 stars belonging to 36 open clusters to determine the atmospheric parameters and chemical abundances with two independent methods: equivalent widths and spectral synthesis. The sample was complemented with 63 clusters with high-resolution spectroscopy from literature. Results. We measured LTE abundances for 21 elements: α (Mg, Si, Ca, and Ti), odd-Z (Na and Al), Fe-peak (Fe, Sc, V, Cr, Mn, Co, Ni, Cu, and Zn), and neutron-capture (Sr, Y, Zr, Ba, Ce, and Nd). We also provide non-local thermodynamic equilibrium abundances for elements when corrections are available. We find inner disk young clusters enhanced in [Mg/Fe] and [Si/Fe] compared to other clusters of their age. For [Ba/Fe], we report an age trend flattening for older clusters (age < 2.5 Ga). The studied elements follow the expected radial gradients as a function of their nucleosynthesis groups, which are significantly steeper for the oldest systems. For the first time, we investigate the existence of an azimuthal gradient, finding some hints of its existence among the old clusters (age > Ga).