arXiv subjects

Henrik Jönsson

Publications and source records attributed to Henrik Jönsson.

At least 19 recordsLinked to original sources

arXiv2026

Stellar Population Astrophysics (SPA) with the TNG. Beyond the iron peak: Galactic evolution of molybdenum, ruthenium and zirconium through open clusters

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, 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 estimate 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, 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.

astro-ph.GA↗

arXiv2026

PySME v1.0: improved modelling of stellar spectra for survey-scale applications

Stellar abundance analysis relies on flexible, high-performance spectral synthesis. To meet these needs, we present PySME v1.0, an updated Python implementation of Spectroscopy Made Easy (SME) designed for precise and survey-scale modelling of stellar spectra.A central challenge in SME based synthesis is the efficient treatment of very large line lists, including both the preselection of negligible lines and the subsequent formal synthesis. PySME v1.0 introduces a revised line-selection framework based on opacity ratio and line depth, together with dynamic line list construction and control of the effective wavelength span over which each line contributes to the synthetic spectrum. These workflows support parallel preprocessing of weak-line selection and reduce the line list passed to the synthesis core, thereby improving scalability while preserving synthetic accuracy. PySME v1.0 also incorporates an updated equation-of-state treatment that improves the modelling of hydrogen lines, particularly Balmer features, while maintaining close agreement with previous SME results for metal lines. The Python interface has further been extended to support parameter-dependent derived quantities updated during optimisation, and PySME provides non-local thermodynamic equilibrium (NLTE) departure-coefficient grids for 17 elements. Together, these developments establish PySME v1.0 as a robust and efficient framework for high-precision stellar abundance analyses in large spectroscopic surveys.

astro-ph.IM↗

arXiv2026

Classical Cepheids in the Galactic thin disk I. Abundance gradients via non-local thermodynamic equilibrium spectral analysis

Classical Cepheids (CCs) have long been considered excellent tracers of the chemical evolution of the Milky Way's young disk. We present a homogeneous, NLTE spectroscopic analysis of 401 Galactic CCs, based on 1,351 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 derive atmospheric parameters and abundances for key species tracing multiple nucleosynthetic channels. Our sample-the largest CC NLTE dataset to date-achieves high internal precision and enables robust modeling 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, and we also apply Gaussian Process 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 behavior rather than by single-slope linear models: logarithmic fits generally outperform simple linear models, while bilinear fits yield inconsistent break radii across elements. Gaussian Process 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. Comparison with recent literature shows overall agreement but highlights 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.

astro-ph.GA↗

arXiv2025

Stellar Population Astrophysics (SPA) with the TNG 23 IR elemental abundances of 114 giant stars in 41 Open Clusters

Open clusters have been extensively used as tracers of Galactic chemical evolution, as their constituent stars possess shared characteristics, including age, Galactocentric radius, metallicity, and chemical composition. By examining the trends of elemental abundances with metallicity, age, and Galactocentric radius, valuable insights can be gained into the distribution and nucleosynthetic origins of chemical elements across the Galactic disc. The infrared domain in particular facilitates the observation of some elemental abundances that can be challenging or impossible to discern in the optical, for example K and F. The objective of this study is to derive the stellar parameters and elemental abundances of up to 23 elements in 114 stars spanning 41 open clusters using high-resolution infrared spectroscopy. In addition, the present study aims to examine the chemical evolution of the Galactic disc. This is achieved by investigating radial abundance gradients, variations in abundance between clusters, and the dependence of chemical abundances on cluster age.

astro-ph.GA↗

arXiv2025

A Galactic Self-Portrait: Density Structure and Integrated Properties of the Milky Way Disk

The evolution history of the Milky Way disk is imprinted in the ages, positions, and chemical compositions of individual stars. In this study, we derive the intrinsic density distribution of different stellar populations using the final data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A total of 203,197 red giant branch stars are used to sort the stellar disk ($R \leq 20$ kpc) into sub-populations of metallicity ($Δ$[M/H]$= 0.1$ dex), age ($Δ\log(\frac{\textrm{age}}{\textrm{yr}})= 0.1$), and $α$-element abundances ([$α$/M]). We fit the present-day structural parameters and density distribution of each stellar sub-population after correcting for the survey selection function. The low-$α$ disk is characterized by longer scale lengths and shorter scale heights, and is best fit by a broken exponential radial profile for each population. The high-$α$ disk is characterized by shorter scale lengths and larger scale heights, and is generally well-approximated by a single exponential radial profile. These results are applied to produce new estimates of the integrated properties of the Milky Way from early times to the present day. We measure the total stellar mass of the disk to be $5.27^{+0.2}_{-1.5} \times 10^{10}$ M$_\odot$ and the average mass-weighted scale length is $R_{d} = 2.37 \pm 0.2$ kpc. The Milky Way's present-day color of $(g-r) = 0.72 \pm 0.02$ is consistent with the classification of a red spiral galaxy, although it has only been in the "green valley" region of the galaxy color-mass diagram for the last $\sim 3$ Gyr.

astro-ph.GA↗

arXiv2025

Rubidium Abundances in Cool Giants from High-Resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution

The Galactic Center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the set of elements measurable in the near-IR, especially neutron-capture elements, improves our ability to trace nucleosynthesis and Galactic chemical evolution. This work aims to identify and characterize a spectral line suitable for determining rubidium (Rb) abundances. Rb is produced in roughly equal parts by the r- and s-processes. We analyze high-resolution (R = 45,000) IGRINS near-IR spectra of 40 M giants in the solar neighborhood, most observed with Gemini South. We perform spectral synthesis of the Rb I line at 15289.48 A, using new log(gf) values and including an astrophysical calibration of the blending Fe I lines. The resulting [Rb/Fe] ratios are compared to other neutron-capture elements and interpreted with chemical evolution models. We demonstrate that the used Rb line is a reliable abundance indicator in M giants and the coolest K giants, but becomes too weak at higher temperatures. [Rb/Fe] shows a decreasing trend with metallicity, mirroring that of ytterbium (Yb), another mixed r-/s-process element. Our results agree with optical studies, validating the use of this near-IR line. Comparisons with chemical evolution models confirm that both s- and r-process sources are needed to explain the Rb trend. This work adds Rb to the list of elements measurable in high-resolution H- and K-band spectra, enabling studies of one more neutron-capture element in dust-obscured regions like the Galactic Center and inner disk.

astro-ph.GA↗

arXiv2025

The elderly among the oldest: new evidence for extremely metal-poor RR Lyrae stars

We performed a detailed spectroscopic analysis of three extremely metal-poor RR Lyrae stars, exploring uncharted territories at these low metallicities for this class of stars. Using high-resolution spectra acquired with HARPS-N at TNG, UVES at VLT, and PEPSI at LBT, and employing Non-Local Thermodynamic Equilibrium (NLTE) spectral synthesis calculations, we provide abundance measurements for Fe, Al, Mg, Ca, Ti, Mn, and Sr. Our findings indicate that the stars have metallicities of [Fe/H] = -3.40 \pm 0.05, -3.28 \pm 0.02, and -2.77 \pm 0.05 for HD 331986, DO Hya, and BPS CS 30317-056, respectively. Additionally, we derived their kinematic and dynamical properties to gain insights into their origins. Interestingly, the kinematics of one star (HD 331986) is consistent with the Galactic disc, while the others exhibit Galactic halo kinematics, albeit with distinct chemical signatures. We compared the [Al/Fe] and [Mg/Mn] ratios of the current targets with recent literature estimates to determine whether these stars were either accreted or formed in situ, finding that the adopted chemical diagnostics are ineffective at low metallicities ([Fe/H] $\lesssim -$1.5). Finally, the established horizontal branch evolutionary models, indicating that these stars arrive at hotter temperatures on the Zero-Age Horizontal Branch (ZAHB) and then transition into RR Lyrae stars as they evolve, fully support the existence of such low-metallicity RR Lyrae stars. As a consequence, we can anticipate detecting more of them when larger samples of spectra become available from upcoming extensive observational campaigns.

astro-ph.SR↗

arXiv2024

Carbon enrichment in APOGEE disk stars as evidence of mass transfer in binaries

Carbon abundances in first-ascent giant stars are usually lower than those of their main-sequence counterparts. At moderate metallicities, stellar evolution of single stars cannot account for the existence of red-giant branch stars with enhanced carbon abundances. The phenomenon is usually interpreted as resulting from past mass transfer from an evolved binary companion now in the white dwarf evolutionary stage. Aims: We aim to confirm the links between [C/O] enhancement, s-process element enhancement and binary fraction using large-scale catalogues of stellar abundances and probable binary stars. Methods: We use a large data set from the 17 data release of the SDSS-IV/APOGEE~2 survey to identify carbon-enhanced stars in the Galactic disk. We identify a continuum of carbon enrichment throughout three different sub-populations of disk stars and explore links between the degree of carbon enrichment and binary frequency, metallicity and chemical compositions. Results: We verify a clear correlation between binary frequency and enhancement in the abundances of both carbon and cerium, lending support to the scenario whereby carbon-enhanced stars are the result of mass transfer by an evolved binary companion. In addition, we identify clustering in the carbon abundances of high-$α$ disk stars, suggesting that those on the high metallicity end are likely younger, in agreement with theoretical predictions for the presence of a starburst population following the gas-rich merger of the Gaia-Enceladus/Sausage system.

astro-ph.GA↗

arXiv2024

Exploring fluorine chemical evolution in the Galactic disk: the open cluster perspective

Open clusters are ideal tools for tracing the abundances of different elements because their stars are expected to have the same age, distance, and metallicity. Therefore, they serve as very powerful tracers for investigating the cosmic origins of elements. This paper expands on a recent study by us, where the element Fluorine was studied in seven previously open clusters, adding six open clusters as well as eight field stars. The primary objective is to determine the abundance of fluorine (F) to gain insight into its production and evolution. The magnesium (Mg) abundances were derived to categorize the field stars into high and low alpha disk populations. Additionally, cerium (Ce) abundances are determined to better understand the interplay between F and s-process elements. The spectra were obtained from the high-resolution near-infra-red GIANO-B instrument at the Telescopio Nazionale Galileo (TNG). For the derivation of the stellar parameters and abundances, the Python version of Spectroscopy Made Easy (PySME) was used. OH, CN, and CO molecular lines and band heads along with Fe I lines were used to determine the stellar parameters in the H-band region. Two HF lines in the K-band (λλ 2.28, 2.33 μm), three K-band Mg I lines (λλ 2.10, 2.11, 2.15 μm), and two Ce II lines in the H-band (λλ 1.66, and 1.71 μm) were used to derive the abundances of F, Mg, and Ce, respectively. F, Mg, and Ce abundances were derived for 14 stars from 6 OCs, as well as 8 field stars. The F and Ce abundances were investigated as a function of metallicity, age, and Galactocentric distances. Our results indicate that asymptotic giant branch stars and massive stars, including a subset of fast rotators (whose rotation speed likely increases as metallicity decreases), are necessary to explain the cosmic origin of F.

astro-ph.GA↗

arXiv2024

A perspective on the Milky Way Bulge-Bar as seen from the neutron-capture elements Cerium and Neodymium with APOGEE

This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of $\sim$2000 stars in the Galactic Bulge/bar spatially contained within $|X_{Gal}|<$5 kpc, $|Y_{Gal}|<$3.5 kpc, and $|Z_{Gal}|<$1 kpc, and spanning metallicities between $-$2.0$\lesssim$[Fe/H]$\lesssim$+0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our Bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd]$<$0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of Bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the Bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magneto-rotational supernovae.

astro-ph.GA↗

arXiv2024

Stellar Population Astrophysics (SPA) with TNG, Fluorine abundances in seven open clusters

The age, evolution, and chemical properties of the Galactic disk can be effectively ascertained using open clusters. Within the large program Stellar Populations Astrophysics at the Telescopio Nazionale Galileo, we specifically focused on stars in open clusters, to investigate various astrophysical topics, from the chemical content of very young systems to the abundance patterns of lesser studied intermediate-age and old open clusters. We investigate the astrophysically interesting element fluorine (F), which has an uncertain and intriguing cosmic origin. We also determine the abundance of cerium (Ce), as F abundance is expected to correlate with the s-process elements. High-resolution near-infrared spectra were obtained using the GIANO-B spectrograph. The Python version of Spectroscopy Made Easy (PySME), was used to derive atmospheric parameters and abundances. The stellar parameters were determined using OH, CN, and CO molecular lines along with Fe I lines. This paper presents the first F Galactic radial abundance gradient. Our results are also compared with literature estimates and with Galactic chemical evolution models that have been generated using different F production channels. Our results indicate a constant, solar pattern in the [F/Fe] ratios across clusters of different ages, supporting the latest findings that fluorine levels do not exhibit any secondary behavior for stars with solar or above-solar metallicity. By comparing our sample stars with the predictions of Galactic chemical evolution models, we came to the conclusion that both asymptotic giant branch stars and massive stars, including a fraction of fast rotators that increase with decreasing metallicity, are needed to explain the cosmic origin of F.

astro-ph.GA↗

arXiv2023

The APOGEE Value Added Catalogue of Galactic globular cluster stars

We introduce the SDSS/APOGEE Value Added Catalogue of Galactic Globular Cluster (GC) Stars. The catalogue is the result of a critical search of the APOGEE data release 17 (DR17) catalogue for candidate members of all known Galactic GCs. Candidate members are assigned to various GCs on the basis of position on the sky, proper motion, and radial velocity. The catalogue contains a total of 7,737 entries for 6,422 unique stars associated with 72 Galactic GCs. Full APOGEE DR17 information is provided, including radial velocities and abundances for up to 20 elements. Membership probabilities estimated on the basis of precision radial velocities are made available. Comparisons with chemical compositions derived by the GALAH survey, as well as optical values from the literature, show good agreement. This catalogue represents a significant increase in the public database of GC star chemical compositions and kinematics, providing a massive homogeneous data set that will enable a variety of studies. The catalogue in fits format is available for public download from the SDSS-IV DR17 value added catalogue website.

astro-ph.GA↗

arXiv2023

A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), $α$-element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low-$α$ disk, high-$α$ disk, and total population independently. The low-$α$ disk exhibits a negative radial metallicity gradient of $-0.06 \pm 0.001$ dex kpc$^{-1}$, which flattens with distance from the midplane. The high-$α$ disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]-[Fe/H] plane and in the [Mg/Fe]-age relation persist across the entire disk. The age estimates have typical uncertainties of $\sim0.15$ in $\log$(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.

astro-ph.GA↗

arXiv2023

Chemical clocks and their time zones: understanding the [s/Mg]--age relation with birth radii

The relative enrichment of s-process to $α$-elements ([s/$α$]) has been linked with age, providing a potentially useful avenue in exploring the Milky Way's chemical evolution. However, the age--[s/$α$] relationship is non-universal, with dependencies on metallicity and current location in the Galaxy. In this work, we examine these chemical clock tracers across birth radii ($\rm \text{R}_\text{birth}$), recovering the inherent trends between the variables. We derive $\rm \text{R}_\text{birth}$ and explore the [s/$α$]--age--$\rm \text{R}_\text{birth}$ relationship for 36,652 APOGEE DR17 red giant and 24,467 GALAH DR3 main sequence turnoff and subgiant branch disk stars using [Ce/Mg], [Ba/Mg], and [Y/Mg]. We discover that the age--[s/Mg] relation is strongly dependent on birth location in the Milky Way, with stars born in the inner disk having the weakest correlation. This is congruent with the Galaxy's initially weak, negative [s/Mg] radial gradient, which becomes positive and steep with time. We show that the non-universal relations of chemical clocks is caused by their fundamental trends with $\rm \text{R}_\text{birth}$ over time, and suggest that the tight age--[s/Mg] relation obtained with solar-like stars is due to similar $\rm \text{R}_\text{birth}$ for a given age. Our results are put into context with a Galactic chemical evolution model, where we demonstrate the need for data-driven nucleosynthetic yields.

astro-ph.GA↗

arXiv2023

A mean-field theory approach to 3D nematic phase transitions in microtubules

Microtubules are dynamic intracellular fibers that have been observed experimentally to undergo spontaneous self-alignment. We formulate a 3D mean-field theory model to analyze the nematic phase transition of microtubules growing and interacting within a 3D space then make a comparison with computational simulations. We identify a control parameter $G_\text{eff}$ and predict a unique critical value $G_\text{eff}=1.56$ for which a phase transition can occur. Furthermore, we show both analytically and using simulations that this predicted critical value does not depend on the presence of zippering. The mean-field theory developed here provides an analytical estimate of microtubule patterning characteristics without running time-consuming simulations and is a step towards bridging scales from microtubule behavior to multicellular simulations.

physics.bio-ph↗

arXiv2023

Stellar Characterization and Radius Inflation of Hyades M Dwarf Stars From the APOGEE Survey

We present a spectroscopic analysis of a sample of 48 M dwarf stars ($0.2 M_{\odot}< M < 0.6 M_{\odot}$) from the Hyades open cluster using high-resolution H-band spectra from the SDSS/APOGEE survey. Our methodology adopts spectrum synthesis with LTE MARCS model atmospheres, along with the APOGEE DR17 line list, to determine effective temperatures, surface gravities, metallicities, and projected rotational velocities. The median metallicity obtained for the Hyades M dwarfs is [M/H]= 0.09$\pm$0.03 dex, indicating a small internal uncertainty and good agreement with optical results for Hyades red-giants. Overall, the median radii are larger than predicted by stellar models by 1.6$\pm$2.3\% and 2.4$\pm$2.3\%, relative to a MIST and DARTMOUTH isochrone, respectively. We emphasize, however, that these isochrones are different and the fractional radius inflation for the fully- and partially-convective regimes have distinct behaviors depending on the isochrone. Using a MIST isochrone there is no evidence of radius inflation for the fully convective stars, while for the partially convective M-dwarfs the radii are inflated by 2.7$\pm$2.1\%, which is in agreement with predictions from models that include magnetic fields. For the partially-convective stars, rapid-rotators present on average higher inflation levels than slow-rotators. The comparison with SPOTS isochrone models indicates that the derived M dwarf radii can be explained by accounting for stellar spots in the photosphere of the stars, with 76\% of the studied M dwarfs having up to 20\% spot coverage, and the most inflated stars with $\sim$20 -- 40\% spot coverage.

astro-ph.SR↗

arXiv2023

A Comparative Analysis of the Chemical Compositions of Gaia-Enceladus/Sausage and Milky Way Satellites using APOGEE

We use data from the 17th data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to contrast the chemical composition of the recently discovered Gaia Enceladus/Sausage system (GE/S) to those of ten Milky Way (MW) dwarf satellite galaxies: LMC, SMC, Boötes I, Carina, Draco, Fornax, Sagittarius, Sculptor, Sextans and Ursa Minor. Our main focus is on the distributions of the stellar populations of those systems in the [Mg/Fe]-[Fe/H] and [Mg/Mn]-[Al/Fe] planes, which are commonly employed in the literature for chemical diagnosis and where dwarf galaxies can be distinguished from in situ populations. We show that, unlike MW satellites, a GE/S sample defined purely on the basis of orbital parameters falls almost entirely within the locus of "accreted" stellar populations in chemical space, which is likely caused by an early quenching of star formation in GE/S. Due to a more protracted history of star formation, stars in the metal-rich end of the MW satellite populations are characterized by lower [Mg/Mn] than those of their GE/S counterparts. The chemical compositions of GE/S stars are consistent with a higher early star formation rate than MW satellites of comparable and even higher mass, suggesting that star formation in the early universe was strongly influenced by other parameters in addition to mass. We find that the direction of the metallicity gradient in the [Mg/Mn]-[Al/Fe] plane of dwarf galaxies is an indicator of the early star formation rate of the system

astro-ph.GA↗

arXiv2022

The chemical characterisation of halo substructure in the Milky Way based on APOGEE

Galactic haloes in a $Λ$-CDM universe are predicted to host today a swarm of debris resulting from cannibalised dwarf galaxies. The chemo-dynamical information recorded in their stellar populations helps elucidate their nature, constraining the assembly history of the Galaxy. Using data from APOGEE and \textit{Gaia}, we examine the chemical properties of various halo substructures, considering elements that sample various nucleosynthetic pathways. The systems studied are Heracles, \textit{Gaia}-Enceladus/Sausage (GES), the Helmi stream, Sequoia, Thamnos, Aleph, LMS-1, Arjuna, I'itoi, Nyx, Icarus, and Pontus. Abundance patterns of all substructures are cross-compared in a statistically robust fashion. Our main findings include: {\it i)} the chemical properties of most substructures studied match qualitatively those of dwarf Milky Way satellites, such as the Sagittarius dSph. Exceptions are Nyx and Aleph, which are chemically similar to disc stars, implying that these substructures were likely formed \textit{in situ}; {\it ii)} Heracles differs chemically from {\it in situ} populations such as Aurora and its inner halo counterparts in a statistically significant way. The differences suggest that the star formation rate was lower in Heracles than in the early Milky Way; {\it iii)} the chemistry of Arjuna, LMS-1, and I'itoi is indistinguishable from that of GES, suggesting a possible common origin; {\it iv)} all three Sequoia samples studied are qualitatively similar. However, only two of those samples present chemistry that is consistent with GES in a statistically significant fashion; {\it v)} the abundance patterns of the Helmi stream and Thamnos are different from all other halo substructures.

astro-ph.GA↗