arXiv subjects

E. Spitoni

Publications and source records attributed to E. Spitoni.

At least 19 recordsLinked to original sources

arXiv2026

Reassessing the low-$\alpha$ massive sequence stars in Gaia RVS

Recently, a chemically depleted young massive stellar population was identified using the spectroscopic catalogue of Gaia DR3. To explain its characteristics, a recent enhanced star formation event, via a third infall occurring within the last 2 Gyr, has been evoked. In this paper we reassess the low alpha sequence of massive stars identified in the Gaia spectroscopic catalog and investigate their presence in other Milky Way spectroscopic survey catalogs. We select massive sequence stars and RGB stars from the Gaia DR3 catalogue using the same filtering strategy adopted in previous chemical cartography studies. These samples are then cross matched with APOGEE DR17, GALAH DR4, and Gaia CNN to enable a detailed comparison of stellar parameters and alpha abundances. Stellar masses are estimated by projecting their atmospheric parameters and infrared magnitudes onto PARSEC isochrones. For the massive star sample, we find large discrepancies in stellar parameters and calcium abundances between Gaia DR3 and the three external surveys. The external catalogues do not show a low ca sequence but rather resemble those of thin disc RGB stars. Other alpha elements (si in APOGEE and GALAH, and mg in GALAH) also do not show depleted values. In APOGEE, however, massive sequence stars with metallicities above -0.5 dex display lower mg abundances. We attribute this to APOGEE's use of macroturbulence velocities calibrated solely on metallicity. Our analysis does not show any evidence for alpha element depletion in massive sequence stars. Alpha abundances of massive sequence stars derived from the Gaia RVS spectra should therefore be used with caution. Nevertheless, the previously proposed three infall chemical evolution models remain plausible: even without a chemically depleted young massive population, scenarios involving only mild dilution could still account for recent star formation episodes.

astro-ph.GA↗

arXiv2026

The effects of yields from binary massive stars as functions of metallicity

Massive stars in binary systems that undergo mass transfer during their lifetime have a different evolution from that of single stars, possibly affecting their chemical yields. While massive stars produce most of the metals in the Universe, only few studies have investigated the effects of massive binary stars on the chemical evolution of the Milky Way. Following the most recent studies on massive binary-stripped star yields as functions of metallicity, we aim at improving previous results based on single-metallicity model grids. Here, by adopting a detailed model of chemical evolution for our Galaxy, we compute the evolution of 22 chemical species including C, N, O, $\alpha$-elements and Fe-peak elements, adopting novel prescriptions for single and binary massive star yields. Our main results can be summarised as follows: (i) consistently with previous predictions, we observe very small differences in both the predicted solar abundances and [X/Fe] vs [Fe/H] relations even when including massive binary yields depending on metallicity; (ii) when adopting the new set of stellar yields for massive single stars, as computed by Farmer et al. (2023), we are able to reproduce both the K solar abundance as well as the [K/Fe] vs [Fe/H] relation, without invoking ad hoc assumptions on nucleosynthesis prescriptions; (iii) our model adopting Farmer's yields both for single and binary massive stars is able to better reproduce the [X/Fe] versus [Fe/H] relation for both Mg and Ca, as compared with standard nucleosynthetic yields adopted in chemical evolution models; iv) we find that no models can well reproduce the [C/Fe] and [Ti/Fe] vs [Fe/H] when adopting the new yields as functions of metallicity.

astro-ph.GA↗

arXiv2026

Co-evolution of the Milky Way high- and low-{\alpha} sequences with chemical evolution models

Observational data have revealed a clear dichotomy in the [{\alpha}/Fe] vs. [Fe/H] diagram of the Milky Way thick and thin disc stars. Many recent studies have shown evidences of a co-evolution phase between the high- and low-{\alpha} disc sequences as well as the presence of very old low-{\alpha} stars. We aim to revise the parallel chemical evolution model that assumes two parallel histories of star formation for the two discs, by considering a pre-enriched delayed second infall episode in our revised scenario. By means of our chemical evolution models, we aim to explore the effects of a phase of co-evolution and the presence of old low-{\alpha} stars, as recently observed. We consider a new version of the parallel scenario for the Milky Way thick and thin disc formation, which consists into two distinct infall episodes of slightly pre-enriched gas. The gas is considered to be extragalactic but possibly contaminated by chemically enriched gas of a massive dwarf galaxy as Gaia-Enceladus, which merged with the Milky Way at least 10 Gyrs ago. Moreover, we test in our model observationally derived star formation histories of kinematically selected thick and thin discs, suggesting that the star formation is triggered by the passages of the Sagittarius galaxy. Our models can well explain the [{\alpha}/Fe] vs. [Fe/H] diagram from APOGEE DR17. Our revised chemical evolution model with a pre-enriched and delayed (roughly 1 Gyr) second infall episode, explains not only the abundance patterns of high- and low-{\alpha} stars but also stellar age distributions for the selected observational sample. We predict a short co-evolution period in between the two phases and we can explain the observed old low-{\alpha} stars, but still further data for precise stellar ages would be needed to put more stringent constraints on their physical nature.

astro-ph.GA↗

arXiv2026

The LEGARE Project. I. Chemical evolution model of the Nuclear Stellar Disc in a Bayesian framework

The Nuclear Stellar Disc (NSD) of the Milky Way is a dense, rotating stellar system in the central 200 pc. The NSD is thought to be primarily fuelled by bar-driven gas inflows from the inner Galactic disc. As part of the LEGARE project, we construct the first chemical evolution models for the NSD using a Bayesian approach tailored to reproduce the observed metallicity distribution functions (MDFs) and compared with the available abundance ratios for Mg, Si, Ca relative to Fe. We adopt a state-of-the-art chemical evolution model in which the gas responsible for the formation of the NSD is assumed to be driven by the Galactic bar-induced inflows. The chemical composition of the accreted material is assumed to reflect that of the Galactic disc at a radius of 4 kpc. A Bayesian MCMC framework is used to fit the MDFs of different samples of NSD stars. If we take the NSD data at face value, without considering a possible contamination from bulge stars, we find that a formation scenario based on the inner disc flowing gas is inconsistent with the low metallicity tail of the observed MDF. This is because the inner disc metallicity, at the epoch of bar formation, was already near solar. On the other hand, models invoking dilution from additional metal-poor inflows successfully reproduce the observations. The best-fit model requires inflow metallicity 5 times lower than the inner disc and a moderate star formation efficiency. The same model successfully reproduces the observed [$\alpha$/Fe] vs. [Fe/H] ratios and predicts a star formation history consistent with the most recent estimates. However, if we assume that the MDF is contaminated by metal poor bulge stars and restricted to [Fe/H] > -0.3 dex, gas dilution is no longer required. In this case, the best-fit model has a very low star formation efficiency and a mild galactic wind.

astro-ph.GA↗

arXiv2026

On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid

We introduce a new photometric catalog of RR Lyrae variables (RRLs, $\sim$300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and Blue Horizontal Branch [BHB] stars ever collected. This includes radial velocity measurements ($\sim$16,000) and iron abundances ($\Delta$S method for 8,140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated to the main Galactic components and their iron distribution function (IDF) becomes more metal-rich when moving from the Halo ([Fe/H]=-1.56) to the Thick (TCD; [Fe/H]=-1.47) and Thin (TND; [Fe/H]=-0.73) disk. Furthermore, Halo RRLs and RRLs in retrograde orbits are $\alpha$-enhanced ([$\alpha$/Fe]=0.27, $\sigma$=0.18), while TCD RRLs are either $\alpha$-enhanced ([Fe/H]$\le$-1.0) or $\alpha$-poor ([Fe/H]$>$-1.0), and TND RRLs are mainly $\alpha$-poor ([$\alpha$/Fe]=-0.01, $\sigma$=0.20). We also identified RRLs associated to the main stellar streams (Gaia-Sausage-Enceladus [GSE]; Sequoia, Helmi, Sagittarius) and we found that their IDFs are quite similar to Halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their $\alpha$-element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD and Halo RRLs is negative and it decreases from -0.026, to -0.010, and to -0.002 dex/kpc. The iron radial gradient based on dry Halo (Halo without substructures) RRLs is, within the errors, equal to the global Halo. We also found a strong similarity between iron and [$\alpha$/Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples.

astro-ph.GA↗

arXiv2025

Elemental abundance ratios for the bulge of M31

We present radial trends of metallicity ([Fe/H]) and abundance ratios ([X/Fe]) for several chemical elements -- including C, N, Na, and the so-called alpha-elements (O, Mg, Si, Ca, and Ti) -- in the bulge of M31, out to ~0.6kpc from the center. We estimated abundances using full-spectrum fitting, full-index fitting, and line-strength analysis, in combination with different stellar population models. We first tested these techniques on mock spectra and SDSS stacked spectra of ETGs, and then applied them to high-quality long-slit spectroscopy of the M31 bulge obtained with the OSIRIS spectrograph at the GTC. We find that O, N, and Na are significantly enhanced relative to Fe across the bulge, with typical abundances >0.3~dex. In particular, N and Na show steep central enhancements, reaching ~0.5dex. C, Mg, and Si exhibit intermediate enhancements of [X/Fe]~0.2dex, with C and Mg decreasing toward the center to <~0.1dex; while Ca, and to a lesser extent Ti, closely follow Fe, with [X/Fe]<0.1dex. Applying the same analysis to SDSS stacked spectra of ETGs revealed that the abundance pattern of the M31 bulge closely resembles that of the most massive galaxies, except for N, which is significantly more enhanced (by ~0.1dex) in the bulge. For the bulk of the bulge, chemical evolution models assuming high star-formation efficiency and a short gas infall timescale reproduce the overall trends in [Fe/H] and [X/Fe]. In the central region (<~100pc), the high metallicity content of the bulge can be explained by either an IMF flatter than Salpeter at high mass, or a prolonged star formation. Additional processes, such as differential galactic winds, appear necessary to account for the observed decoupling among alpha elements and the strong central N enhancement. Our results support a scenario whereby the bulk of the M31 bulge formed during a fast and intense episode of star formation.

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arXiv2025

Shaping Galactic Habitability: the impact of stellar migration and gas giants

In exoplanet research, the focus is increasingly on identifying Earth analogs, planets similar in density and habitability potential. As the number of rocky exoplanets grows, parallel discussions have emerged on system architectures and Galactic environments that may support life, drawing comparisons to our own Earth. This has brought renewed attention to the concept of the Galactic Habitable Zone (GHZ) as a broader context for interpreting the diversity of planetary environments. This study is the first to use detailed chemical evolution models to investigate the impact of stellar migration, modeled through a parametric approach, on the GHZ. Our findings reveal that stellar migration significantly enhances the number of stars capable of hosting habitable planets in the outer Galactic regions, with an increase of up to a factor of five at 18 kpc relative to a baseline value of unity at 6 kpc. Furthermore, we explore a novel scenario where the presence of gas giant planets increases the probability for the formation of terrestrial ones. We find that this increased probability is higher in the inner Galactic disc, but is also mitigated by stellar migration. In particular, at the present time, the number of FGK stars hosting terrestrial planets with minimum habitability conditions in the ring centered at 4 kpc is approximately 1.4 times higher than in scenarios where gas giants are assumed to hinder the formation and evolution of Earth-like planets. Without stellar migration, this factor increases to 1.5. Even larger ratios are predicted for terrestrial planets orbiting retired A stars, reaching 2.8 in models with stellar migration and 3.3 in models without it.

astro-ph.GA↗

arXiv2025

The Galactic inner spiral arms revealed by the Gaia ESO Survey chemical abundances. Metallicity and [Mg/Fe] ratios

Recent observational advances, such as Gaia DR3 GSP-Spec, have highlighted the potential of chemical abundances in tracing and revealing the structure of spiral arms. Building on these studies, we aim to trace the Milky Way's inner spiral arms using chemical abundance data from the Gaia-ESO Survey (GES). By mapping over-densities in [Fe/H] and [Mg/Fe], we seek to identify spiral arms in both radial and vertical planes, detect substructures, and compare our results with recent Galactic chemical evolution models. We used chemical abundance data from the Gaia-ESO Survey to create spatial maps of [Fe/H], [Mg/H], and [Mg/Fe] excess across the Galactic inner disc. We compared our results with the spiral arm models proposed by Spitoni et al. (2023) and Barbillon et al. (2024). For the first time, the inner spiral arms were revealed using chemical abundance patterns. We detected [Fe/H] enhancements and [Mg/Fe] under-abundances that consistently trace the Scutum and Sagittarius arms. A connecting spur between these arms is observed in the [Mg/H] plane. The alignment between our observations and the results of our 2D chemical evolution models reinforces the significance of spiral arm transits in driving both azimuthal and radial variations in chemical abundances. Our results confirm that spiral arms can be traced using stellar chemical abundances with GES data, providing a new perspective on the structure of the inner Galaxy. The consistency between enhanced [Fe/H] and lower [Mg/Fe] ratios, as observed in previous studies, further strengthens the reliability of our findings. The observed spur, bifurcation, and vertical substructures align well with recent models and studies, indicating that chemical maps can significantly contribute to our understanding of Galactic spiral arms.

astro-ph.GA↗

arXiv2025

MINCE III. Detailed chemical analysis of the UVES sample

Context. The MINCE (Measuring at Intermediate Metallicity Neutron-Capture Elements) project aims to provide high quality neutron-capture abundances measurements in several hundred stars at intermediate metallicity,-2.5 < [Fe/H] < -1.5. This project will shed light on the origin of the neutron-capture elements and the chemical enrichment of the Milky Way. Aims. The goal of this work is to chemically characterize the second sample of the MINCE project and compare the abundances with the galactic chemical evolution model at our disposal. Methods. We performed a standard abundance analysis based on 1D LTE model atmospheres on high-resolution and high-signal-to-noise-ratio UVES spectra. Results. We provide the kinematic classification (i.e., thin disk, thick disk, thin-to-thick disk, halo, Gaia Sausage Enceladus, Sequoia) of 99 stars and the atmospheric parameters for almost all stars. We derive the abundances for light elements (from Na to Zn) and neutron-capture elements (Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu) in a subsample of 32 stars in the metallicity range -2.5 < Fe/H] < -1.00. In the subsample of 32 stars, we identify 8 active stars exhibiting (inverse) P-Cygni profile and one Li-rich star, CD 28-11039. We find a general agreement between the chemical abundances and the stochastic model computed for the chemical evolution of the Milky Way halo for the elements Mg, Ca, Si, Ti, Sc, Mn, Co, Ni, Zn, Rb, Sr, Y, Zr, Ba, La, and Eu . Conclusions. The MINCE project has already significantly increased the number of neutron-capture elements measurements in the intermediate metallicity range. The results from this sample are in perfect agreement with the previous MINCE sample. The good agreement between the chemical abundances and the chemical evolution model of the Galaxy supports the nucleosynthetic processes adopted to describe the origin of the n-capture elements.

astro-ph.GA↗

arXiv2024

Yields from massive stars in binaries. Chemical evolution of the Milky Way disk

A large fraction of massive stars in the Galaxy reside in binary systems and their evolution is different from that of single stars. The yields of massive stars, which are the main responsible for the production of metals, can be therefore affected by the binary nature of the systems. Recently, Farmer et al. (2023) computed new grids of yields for single and binary-stripped massive stars with solar chemical composition. The main purpose of this paper is to test these yields on the chemical evolution of Galactic stars. To do that, we adopt well-tested chemical evolution models for the Milky Way disk, implementing both yields for single and binary-stripped massive stars. In particular, we assume different percentages of massive binary systems within the initial mass function. We compute the evolution of 22 chemical species starting from $^{4}$He to $^{64}$Zn. Our main results can be summarized as follows: i) when adopting the yields of Farmer et al. (2023), large differences are found relative to the predicted solar abundances by chemical evolution models adopting "standard" massive star yields from the literature for $^{12}$C, $^{14}$N, $^{24}$Mg, $^{39}$K, $^{40}$Ca, $^{55}$Mn and $^{59}$Co. Generally, the yields for single stars reproduce slightly better the observed solar abundances, although for several elements a large fraction of binaries helps in reproducing the observations; ii) different fractions of massive binaries (from 50% to 100%) produce negligible differences in the predicted solar abundances, whereas the differences are more marked between models with and without binary-stripped stellar yields; iii) for the [X/Fe] vs. [Fe/H] relations, the yields including massive stars in binaries produce the best results for $^{52}$Cr, while for $^{12}$C, $^{39}$K, $^{40}$Ca and $^{24}$Mg the best results are obtained with Farmer's yields with no binaries.

astro-ph.GA↗

arXiv2024

Chemical Abundances in the Nuclear Star Cluster of the Milky Way: alpha-Element Trends and Their Similarities with the Inner Bulge

A chemical characterization of the Galactic Center is essential for understanding its formation and structural evolution. Trends of alpha-elements, such as Mg, Si, and Ca, serve as powerful diagnostic tools, offering insights into star-formation rates and gas-infall history. However, high extinction has previously hindered such studies. In this study, we present a detailed chemical abundance analysis of M giants in the Milky Way's Nuclear Star Cluster (NSC), focusing on alpha-element trends with metallicity. High-resolution, near-infrared spectra were obtained using the IGRINS spectrograph on the Gemini South telescope for nine M giants. Careful selection of spectral lines, based on a solar-neighborhood control sample of 50 M giants, was implemented to minimize systematic uncertainties. Our findings show enhanced alpha-element abundances in the predominantly metal-rich NSC stars, consistent with trends in the inner bulge. The NSC stars follow the high-[alpha/Fe] envelope seen in the solar vicinity's metal-rich population, indicating a high star-formation rate. The alpha-element trends decrease with increasing metallicity, also at the highest metallicities. Our results suggest the NSC population likely shares a similar evolutionary history with the inner bulge, challenging the idea of a recent dominant star formation burst. This connection between the NSC and the inner-disk sequence suggests that the chemical properties of extragalactic NSCs of Milky Way type galaxies could serve as a proxy for understanding the host galaxies' evolutionary processes.

astro-ph.GA↗

arXiv2024

Constraints on the history of Galactic spiral arms revealed by Gaia GSP-Spec alpha-elements

The distribution of chemical elements in the Galactic disc can reveal fundamental clues on the physical processes that led to the current configuration of our Galaxy. We map chemical azimuthal variations in the disc using individual stellar chemical abundances and discuss their possible connection with the spiral arms and other perturbing mechanisms. Using Gaia Data Release 3, we examine [Ca/Fe] and [Mg/Fe] fluctuations in a ~4 kpc region around the Sun, focusing on bright giant stars. We implemented a kernel density estimator technique to enhance the chemical inhomogeneities. We observe radial gradients and azimuthal fluctuations in [alpha/Fe] for young (<150 Myr) and old (>2 Gyr) stars, with amplitudes varying according to the studied element. In young stars, those within spiral arms (e.g., Sagittarius-Carina and Local arms) are generally more metal and calcium-rich (~0-0.19 dex) but show lower [Ca/Fe] (~0.06 dex) and [Mg/Fe] (~0.05 dex) compared to inter-arm regions, suggesting enhanced iron production in spiral arms. These [alpha/Fe] depletions are analysed in light of theoretical scenarios and compared to a 2D chemical evolution model with multiple spiral patterns. For the old sample, [Ca/Fe] maps reveal deficiencies along a segment of the Local arm identified by young stars. We caution that, for this old sample, the quality of the obtained maps might be limited along a specific line-of-sight, due to the Gaia scanning law. This study transitions our understanding of disc chemical evolution from a 1D radial view to a more detailed 2D framework incorporating radial, azimuthal, and small-scale variations. Individual chemical abundances prove essential for tracing spiral arms in disc galaxies. We recommend models and simulations incorporate alpha-abundance trends to better address spiral arm lifetimes.

astro-ph.GA↗

arXiv2024

The AMBRE Project: Lead abundance in Galactic stars

The chemical evolution of neutron capture elements in the Milky Way is still a matter of debate. Although more and more studies investigate their chemical behaviour, there is still a lack of a significant large sample of abundances of a key heavy element: lead. Lead is the final product of the s-process nucleosynthesis channel and is one of the most stable heavy elements. We analysed high-resolution spectra from the ESO UVES and FEROS archives. Atmospheric parameters were taken from the AMBRE parametrisation. We used the automated abundance method GAUGUIN to derive lead abundances in 653 slow-rotating FGK-type stars from the 368.34nm Pb I line. We present the largest catalogue of homogeneous LTE and non-LTE lead abundances ever published with metallicities ranging from -2.9 to 0.6dex and [Pb/Fe] from -0.7 to 3.3dex. Within this sample, no lead-enhanced Asymptotic Giant Branch (AGB) stars were found, but nine lead-enhanced metal-poor stars ([Pb/Fe] > 1.5) were detected. Most of them were already identified as carbon-enhanced metal-poor stars with enrichments in other s-process species. The lead abundance of 13 Gaia Benchmark Stars are also provided. We then investigated the Pb content of the Milky Way disc by computing vertical and radial gradients and found a slightly decreasing [Pb/Fe] radial trend with metallicity. This trend together with other related ratios ([Pb/Eu], [Pb/Ba], and [Pb/alpha]) are interpreted thanks to chemical evolution models. The two-infall model closely reproduces the observed trends with respect to the metallicity. It is also found that the AGB contribution to the Pb Galactic enrichment has to be strongly reduced. Moreover, the contribution of massive stars with rather high rotational velocities should be favoured in the low-metallicity regime.

astro-ph.SR↗

arXiv2024

A Census of Sun's Ancestors and their Contributions to the Solar System Chemical Composition

In this work we compute the rates and numbers of different types of stars and phenomena (supernovae, novae, white dwarfs, merging neutron stars, black holes) that contributed to the chemical composition of the Solar System. This process is called "chemical evolution". In particular, we analyse the death rates of stars of all masses, dying either quiescently or explosively. These rates and total star numbers are computed in the context of a revised version of the two-infall model for the chemical evolution of the Milky Way, which reproduces fairly well the observed abundance patterns of several chemical species, the global solar metallicity, and the current gas, stellar, and total surface mass densities. We compute also the total number of stars ever born and still alive as well as the number of stars born up to the formation of the Solar System with a mass and metallicity like the Sun. This latter number will account for all the possible existing Solar Systems which can host life in the solar vicinity. We conclude that, among all the stars (from 0.8 to 100 M$_{\odot}$) born and died from the beginning up to the Solar System formation epoch, which contributed to its chemical composition, 93.00\% are represented by stars dying as single white dwarfs (without interacting significantly with a companion star) and originating in the mass range 0.8-8 M$_{\odot}$, while 5.24$\%$ are neutron stars and 0.73$\%$ are black holes, both originating from supernovae core-collapse (M > 8 M$_{\odot}$); 0.64$\%$ are Type Ia supernovae and 0.40$\%$ are nova systems, both originating from the same mass range as the white dwarfs. The number of stars similar to the Sun born from the beginning up to the Solar System formation, with metallicity in the range 12+log(Fe/H)= 7.50 $\pm$ 0.04 dex is $ \sim 31 \cdot$ 10$^{7}$, and in particular our Sun is the $\sim 2.61 \cdot$ 10$^7$-th star of this kind.

astro-ph.SR↗

arXiv2024

Chemical evolution of the Galactic bulge with different stellar populations

The metallicity distribution function (MDF) of the Galactic bulge features a multi-peak shape, with a metal-poor peak at [Fe/H]=-0.3 dex and a metal-rich peak at [Fe/H]=+0.3 dex. This bimodality is also seen in [alpha/Fe] versus [Fe/H] ratios, indicating different stellar populations in the bulge. We aim to replicate the observed MDF by proposing a scenario where the metal-poor bulge stars formed in situ during an intense star formation burst, while the metal-rich stars formed during a second burst and/or were accreted from the inner Galactic disk due to a growing bar. We used a chemical evolution model that tracks various chemical species with detailed nucleosynthesis, focusing on Fe production from both Type Ia supernovae and massive stars, including rotating massive stars with varying velocities. Our model also accounts for gas infall, outflow, and the effect of stellar migration. Results are compared to 13,000 stars from the SDSS/APOGEE survey within 3.5 kpc of the Galactic center. Our model successfully reproduces the double-peak shape of the bulge MDF and the alpha-element abundance trends relative to Fe by assuming (i) a multi-burst star formation history with a 250 Myr quenching of the first burst and (ii) stellar migration from the inner disk due to a growing bar. We estimate that about 40% of the bulge-bar's stellar mass originates from the inner disk. Nucleosynthesis models that assume either no rotation for massive stars or a rotational velocity distribution favoring slow rotation at high metallicities best match the observed MDF and [alpha/Fe] and [Ce/Fe] versus [Fe/H] abundance patterns.

astro-ph.GA↗

arXiv2024

(Re)mind the gap: a hiatus in star formation history unveiled by APOGEE DR17

The analysis of several spectroscopic surveys indicates the presence of a bimodality between the disc stars in the abundance ratio space of [${\alpha}$/Fe] versus [Fe/H]. The two stellar groups are commonly referred to as the high-${\alpha}$ and low-${\alpha}$ sequences. Some models capable of reproducing such a bimodality, invoke the presence of a hiatus in the star formation history in our Galaxy, whereas other models explain the two sequences by means of stellar migration. Our aim is to show that the existence of the gap in the star formation rate between high-$\alpha$ and low-$\alpha$ is evident in the stars of APOGEE DR17, if one plots [Fe/$\alpha$] versus [$\alpha$/H], thus confirming previous suggestions by Gratton et al. (1996) and Fuhrmann (1998). Then we try to interpret the data by means of detailed chemical models. We compare the APOGEE DR17 red giant stars with the predictions of a detailed chemical evolution model based on the two-infall paradigm, taking also into account possible accretion of dwarf satellites. The APOGEE DR17 abundance ratios [Fe/$\alpha$] versus [$\alpha$/H] exhibit a sharp increase of [Fe/$\alpha$] at a nearly constant [$\alpha$/H] (where $\alpha$ elements considered are Mg, Si, O) during the transition between the two disc phases. This observation strongly supports the hypothesis that a hiatus in star formation occurred during this evolutionary phase. Notably, the most pronounced growth in the [Fe/$\alpha$] versus [$\alpha$/H] relation is observed for oxygen, as this element is exclusively synthesised in core-collapse supernovae. A chemical model predicting a stop in the star formation of a duration of roughly 3.5 Gyr, and where the high-$\alpha$ disc starts forming from pre-enriched gas by a previous encounter with a dwarf galaxy can well explain the observations.

astro-ph.GA↗

arXiv2024

MINCE II. Neutron capture elements

The MINCE (Measuring at Intermediate metallicity Neutron-Capture Elements) project aims to gather the abundances of neutron-capture elements but also of light elements and iron peak elements in a large sample of giant stars in this metallicity range. T The aim of this work is to study the chemical evolution of galactic sub-components recently identified (i.e. Gaia Sausage Enceladus (GSE), Sequoia). We used high signal-to-noise ratios, high-resolution spectra and standard 1D LTE spectrum synthesis to determine the detailed abundances. We could determine the abundances for up to 10 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm and Eu) in 33 stars. The general trends of abundance ratios [n-capture element/Fe] versus [Fe/H] are in agreement with the results found in the literature. When our sample is divided in sub-groups depending on their kinematics, we found that the run of [Sr/Ba] vs [Ba/H] for the stars belonging to the GSE accretion event shows a tight anti-correlation. The results for the Sequoia stars, although based on a very limited sample, shows a [Sr/Ba] systematically higher than the [Sr/Ba] found in the GSE stars at a given [Ba/H] hinting at a different nucleosynthetic history. Stochastic chemical evolution models have been computed to understand the evolution of the GSE chemical composition of Sr and Ba. The first conclusions are that the GSE chemical evolution is similar to the evolution of a dwarf galaxy with galactic winds and inefficient star formation. Detailed abundances of neutron-capture elements have been measured in high-resolution, high signal-to-noise spectra of intermediate metal-poor stars, the metallicity range covered by the MINCE project. These abundances have been compared to detailed stochastic models of galactic chemical evolution.

astro-ph.SR↗

arXiv2024

Cosmic Type Ia SN rate and constraints on SN Ia progenitors

Type Ia supernovae play a key role in the evolution of galaxies by polluting the interstellar medium with a fraction of iron peak elements larger than that released in the core collapse supernova events. Their light-curve, moreover, is widely used in cosmological studies as it constitutes a reliable distance indicator at extra-galactic scales. Among the mechanisms proposed to explain the Type Ia SNe, the single and double degenerate channels are thought to be the dominant ones, which imply a different distribution of time delays between the progenitor formation and the explosion. In this paper, we aim at determining the dominant mechanism by comparing a compilation of Type Ia SN rates with those computed from various cosmic star formation histories coupled with different delay time distribution functions, and evaluating the relative contributions of both channels. By using a least-squares fitting procedure, we model the observations of Type Ia SN rates assuming different combinations of three recent cosmic star formation rates and seven delay time distributions. The goodness of these fits are statistically quantified by the chi-squared test. For two of the three cosmic star formation rates, the single degenerate scenario provides the most accurate explanation for the observations, while a combination of 34% single degenerate and 66% double degenerate delay time distributions is more plausible for the remaining tested cosmic star formation rates. The wide double degenerate scenario mechanism slightly under-predicts the observations at redshift z>1, unless the cosmic SFR flattens in that regime. On the contrary, although the purely close double degenerate scenario can be ruled out, we cannot rule out a mixed scenario with single and double degenerate progenitors.

astro-ph.CO↗