Heavy Element Abundances Research Articles

Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362

ABSTRACT NGC 362 is a non-common Type II Galactic globular cluster, showing a complex pseudo two-colour diagram or ‘chromosome map’. The clear separation of its stellar populations in the colour–magnitude diagram and the distribution of the giant stars in the chromosome map strongly suggests that NGC 362 could host stars with both cluster-nominal, as well as enhanced heavy-element abundances, and one of them could be iron. However, despite previous spectroscopic observations of NGC 362, no such iron variation has been detected. Our main goal is to confirm or disprove this result by searching for any internal variation of [Fe/H], which would give us insight into the formation and evolution of this interesting globular cluster. In this paper, we present the abundance analysis for a sample of 11 red giant branch members based on high-resolution and high S/N spectra obtained with the MIKE echelle spectrograph mounted at the Magellan-Clay telescope. HST and GAIA photometry and astrometry has been used to determine atmospheric parameters and membership. We obtained Teff, log(g), and vt for our target stars and measured the mean iron content of the sample and its dispersion with three different methods, which lead to [Fe/H]1 = −1.10 ± 0.02, [Fe/H]2 = −1.09 ± 0.01, and [Fe/H]3 = −1.10 ± 0.01, while the internal dispersion turned out to be $\sigma _{[\text{Fe/H}]_1}$ = 0.06 ± 0.01, $\sigma _{[\text{Fe/H}]_2}$ = 0.03 ± 0.01, and $\sigma _{[\text{Fe/H}]_3}$ = 0.05 ± 0.01, respectively. The error analysis gives an internal dispersion due to observational error of 0.05 dex. Comparing the observed dispersion with the internal errors, we conclude that NGC 362 does not show any trace of an internal iron spread.

Determination of the Cosmic-Ray Chemical Composition: Open Issues and Prospects

Cosmic rays are relativistic particles that come to the Earth from outer space. Despite a great effort made in both experimental and theoretical research, their origin is still unknown. One of the main keys to understand their nature is the determination of its chemical composition as a function of primary energy. In this paper, we review the measurements of the mass composition above 1015 eV. We first summarize the main aspects of air shower physics that are relevant in composition analyses. We discuss the composition measurements made by using optical, radio, and surface detectors and the limitations imposed by current high-energy hadronic interaction models that are used to interpret the experimental data. We also review the photons and neutrinos searches conducted in different experiments, which, in addition to being important to understand the nature of cosmic rays, can provide relevant information related to the abundance of heavy or light elements in the flux at the highest energies. Finally, we summarize the future composition measurements that are currently being planned or under development.

The internal rotation of the Sun and its link to the solar Li and He surface abundances

The Sun serves as a natural reference for the modelling of the various physical processes at work in stellar interiors. Helioseismology results, which inform us on the characterization of the interior of the Sun (such as, for example, the helium abundance in its envelope), are, however, at odds with heavy element abundances. Moreover, the solar internal rotation and surface abundance of lithium have always been challenging to explain. We present results of solar models that account for transport of angular momentum and chemicals by both hydrodynamic and magnetic instabilities. We show that these transport processes reconcile the internal rotation of the Sun, its surface lithium abundance, and the helioseismic determination of the envelope helium abundance. We also show that the efficiency of the transport of chemicals required to account for the solar surface lithium abundance also predicts the correct value of helium, independently from a specific transport process.

Direct search for primordial 244Pu in Bayan Obo bastnaesite

The abundances of heavy elements produced in r-process nucleosynthesis in the early solar system need experimental verification. 244Pu could be the heaviest primordial nuclide produced before the formation of the Earth still being detectable today. As recent attempts failed to confirm the discovery of 244Pu signals at a concentration of 1.0 × 10−18 g/g in bastnaesite reported by Hoffman et al. in this study, the total primordial 244Pu in 450 g bastnaesite sample from Bayan Obo ore (China) was measured using ultra-sensitive compact accelerator mass spectrometry (AMS). As no 244Pu signal was detected, an upper limit for the 244Pu in our bastnaesite sample was estimated to be 2.1 × 10−20 g/g at 99% confidence level.

METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble Program. III. Interstellar Depletions, Dust-to-Metal, and Dust-to-Gas Ratios versus Metallicity

Abstract The metallicity and gas density dependence of interstellar depletions, the dust-to-gas (D/G), and dust-to-metal (D/M) ratios have important implications for how accurately we can trace the chemical enrichment of the universe, either by using FIR dust emission as a tracer of the ISM or by using spectroscopy of damped Lyα systems to measure chemical abundances over a wide range of redshifts. We collect and compare large samples of depletion measurements in the Milky Way (MW), Large Magellanic Cloud (LMC) (Z = 0.5 Z ⊙), and Small Magellanic Cloud (SMC) (Z = 0.2 Z ⊙). The relations between the depletions of different elements do not strongly vary between the three galaxies, implying that abundance ratios should trace depletions accurately down to 20% solar metallicity. From the depletions, we derive D/G and D/M. The D/G increases with density, consistent with the more efficient accretion of gas-phase metals onto dust grains in the denser ISM. For log N(H) > 21 cm−2, the depletion of metallicity tracers (S, Zn) exceeds −0.5 dex, even at 20% solar metallicity. The gas fraction of metals increases from the MW to the LMC (factor 3) and SMC (factor 6), compensating for the reduction in total heavy element abundances and resulting in those three galaxies having the same neutral gas-phase metallicities. The D/G derived from depletions are respective factors of 2 (LMC) and 5 (SMC) higher than the D/G derived from FIR, 21 cm, and CO emission, likely due to the combined uncertainties on the dust FIR opacity and on the depletion of carbon and oxygen.

Ultra-Refractory Peridotites of Phanerozoic Mantle Origin: the Papua New Guinea Ophiolite Mantle Tectonites

AbstractHarzburgites and dunites forming the base of the Late Cretaceous–Paleocene Papuan Ultramafic Belt (PUB) and Marum ophiolites of Papua New Guinea (PNG) are among the most refractory mantle peridotites on Earth. We present a new integrated dataset of major element, bulk plus mineral trace element and Re–Os isotopic analyses aimed at better understanding the genesis of these peridotites. The PUB harzburgites contain olivine (Fo92–93), low-Al enstatite (less than or equal to 0.5 wt. % Al2O3 and CaO), and Cr-rich spinel (Cr# = 0.90–0.95). The Marum harzburgites are less refractory with olivine (Fo91.9–92.7), enstatite (~0.5–1.0 wt. % Al2O3 and CaO), minor clinopyroxene (diopside), and spinel (Cr# = 0.71–0.77). These major element characteristics reflect equivalent or greater levels of melt depletion than that experienced by Archean cratonic peridotites.Whereas bulk-rock heavy rare earth element (HREE) abundances mirror the refractory character indicated by the mineral chemistry and major elements, large-ion lithophile elements indicate a more complex melting and metasomatic history. In situ olivine and orthopyroxene REE measurements show that harzburgites and dunites have experienced distinct melt-rock interaction processes, with dunite channels/lenses, specifically, showing higher abundances of HREE in olivine. Distinctive severe inter-element fraction of platinum group elements and Re result in complex patterns that we refer to as ‘M-shaped’. These fractionated highly siderophile element (HSE) patterns likely reflect the dissolution of HSE-rich phases in highly depleted peridotites by interaction with subduction-related melts/fluids, possibly high-temperature boninites.Osmium isotope compositions of the PNG peridotites are variable (187Os/188Os = 0.1204 to 0.1611), but fall within the range of peridotites derived from Phanerozoic oceanic mantle, providing no support for ancient melt depletion, despite their refractory character. This provides further evidence that highly depleted peridotites can be produced in the modern Earth, in subduction zone environments. The complex geochemistry indicates a multi-stage process for the formation of the PNG mantle peridotites in a modern geodynamic environment. The first stage involves partial melting at low-pressure (<2 GPa) and high-temperature (~1250°C–1350°C) to form low-K, low-Ti tholeiitic magmas that formed the overlying cumulate peridotite–gabbro and basalt (PUB only) sequences of the ophiolites. This is inferred to have occurred in a fore-arc setting at the initiation of subduction. Later stages involved fluxing of the residual harzburgites with hydrous fluids and melts to form replacive dunites and enstatite dykes and interaction of the residual peridotites in the overlying mantle wedge with high-temperature hydrous melts from the subducting slab to generate the extremely refractory harzburgites. This latter stage can be linked to the eruption of low-Ca boninites at Cape Vogel, and other arc-related volcanics, in a nascent oceanic island arc. Both ophiolites were emplaced shortly after when the embryonic oceanic island arc collided with the Australian continent.

On the possible contribution of cationic oxygenated carbon chains CnO+, HCnO+, and OCnO+ (n = 4–9) to the diffuse interstellar bands

ABSTRACT Only four of the diffuse interstellar bands (DIBs) are currently accounted for, ascribed to electronic transitions of C$_{60}^+$. Investigations into carriers of other DIBs historically focus on charged and neutral hydrocarbons, and little information is available regarding oxygenated carbon and hydrocarbon species that result from the two most abundant heavy elements in the interstellar medium, C and O. In this study, we assess whether CnO+, HCnO+, and OCnO+ (n = 4–9) cations are viable candidates to account for DIBs using both density-functional theory (DFT) and coupled cluster single-double and perturbative triple theory, CCSD(T). For these species, the linear structures are the most stable isomers with the lowest dissociation threshold corresponding to CO loss. Optical absorptions of the oxygenated carbon chain cations are characterized by calculated vertical excitation wavelengths and their corresponding oscillator strengths using the equation-of-motion CCSD (EOM-CCSD) method. Aside from HC4O+ and HC2n +1O+, all of the species considered in this study have calculated electronic transitions that lie in the visible or near-infrared spectral regions. Minimal column densities necessary for these cations to account for DIBs have been estimated. Based on present results and the known column densities for neutral oxygenated carbon chains in TMC-1, the growth rate of charged O-bearing carbon chains via ion-neutral reaction mechanisms is judged to be too low to form a sufficient population to give rise to DIBs.

The peculiar abundances of HE 1005–1439

Context. Understanding the surface chemical composition of carbon-enhanced metal-poor (CEMP) stars with enhanced abundances of heavy elements remains problematic. Aims. One of the primary objectives is to investigate the origin of the peculiar abundance pattern observed in the carbon-enhanced extremely metal-poor object HE 1005–1439, which is enriched with both s-process and i-process nucleosynthesis products and thus forms a new class of object with a distinct abundance pattern. Methods. We performed a detailed, high-resolution spectroscopic analysis of this object based on SUBARU/HDS spectra with a resolution R of ∼50 000. We utilised the line analysis method with measured equivalent widths of neutral and ionised lines due to various elements. Moreover, we calculated the spectrum synthesis of carbon molecular bands and lines due to elements with hyperfine structures to determine the elemental abundances. Abundances of ten light elements from C through Ni and 12 heavy elements Sr, Y, Ba, La, Ce, Pr, Nd, Eu, Dy, Er, Hf, and Pb were determined. We also performed a parametric-model-based analysis of the abundances of the heavy elements to understand the origin of the observed abundance pattern. Results. For the first time, we came across an object with a surface chemical composition that exhibits contributions from both slow (s) and intermediate (i) neutron-capture nucleosynthesis. The observed abundance pattern is quite unique and has never been observed before in any CEMP stars. The star is found to be a CEMP-s star based on the CEMP stars’ classification criteria. However, the observed abundance pattern could not be explained based on theoretical s-process model predictions. On the contrary, our parametric-model based analysis clearly indicates its surface chemical composition being influenced by similar contributions from both the s- and i-process. We critically examined the observed abundances and carefully investigated the formation scenarios involving the s-process and the i-process that are available in literature, and we found that none of them could explain the observed abundances. We note that the variation we see in our radial velocity estimates obtained from several epochs may indicate the presence of a binary companion. Considering a binary system, we therefore propose a formation scenario for this object involving effective proton ingestion episodes triggering i-process nucleosynthesis followed by s-process asymptotic giant branch (AGB) nucleosynthesis with a few third-dredge-up episodes in the now extinct companion AGB star. Results obtained from the parametric-model-based analysis are discussed in light of existing stellar evolutionary models.

Probing Massive Star Nucleosynthesis with Data on Metal-Poor Stars and the Solar System

Metal-poor stars were formed during the early epochs when only massive stars had time to evolve and contribute to the chemical enrichment. Low-mass metal-poor stars survive until the present and provide fossil records of the nucleosynthesis of early massive stars. On the other hand, short-lived radionuclides (SLRs) in the early solar system (ESS) reflect the nucleosynthesis of sources that occurred close to the proto-solar cloud in both space and time. Both the ubiquity of Sr and Ba and the diversity of heavy-element abundance patterns observed in single metal-poor stars suggest that some neutron-capture mechanisms other than the r-process might have operated in early massive stars. Three such mechanisms are discussed: the weak s-process in non-rotating models with initial carbon enhancement, a new s-process induced by rapid rotation in models with normal initial composition, and neutron-capture processes induced by proton ingestion in non-rotating models. In addition, meteoritic data are discussed to constrain the core-collapse supernova (CCSN) that might have triggered the formation of the solar system and provided some of the SLRs in the ESS. If there was a CCSN trigger, the data point to a low-mass CCSN as the most likely candidate. An 11.8 M⊙ CCSN trigger is discussed. Its nucleosynthesis, the evolution of its remnant, and the interaction of the remnant with the proto-solar cloud appear to satisfy the meteoritic constraints and can account for the abundances of the SLRs 41Ca, 53Mn, and 60Fe in the ESS.

MUSE spectroscopy of planetary nebulae with high abundance discrepancies

ABSTRACT We present MUSE deep integral-field unit spectroscopy of three planetary nebulae (PNe) with high-abundance discrepancy factors (ADF > 20): NGC 6778, M 1–42, and Hf 2–2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (Te), electron density (ne), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N ii] and [O ii] lines on Te and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low Te values and a downward gradient of Te are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with ‘normal’ metal content. We have simultaneously constructed, for the first time, the ADF maps of O+ and O2+ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H i emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order.

Planetary core formation via multispecies pebble accretion

ABSTRACT In the general classical picture of pebble-based core growth, planetary cores grow by accretion of single pebble species. The growing planet may reach the so-called pebble isolation mass, at which it induces a pressure bump that blocks inward drifting pebbles exterior to its orbit, thereby stalling core growth by pebble accretion. In recent hydrodynamic simulations, pebble filtration by the pressure bump depends on several parameters including core mass, disc structure, turbulent viscosity and pebble size. We have investigated how accretion of multiple, instead of single, pebble species affects core growth rates, and how the dependence of pebble isolation mass on turbulent viscosity and pebble size sets the final core masses. We performed numerical simulations in a viscous one-dimensional disc, where maximal grain sizes were regulated by grain growth, fragmentation and drift limits. We confirm that core growth rates and final core masses are sensitive to three key parameters: the threshold velocity at which pebbles fragment on collision, the turbulent viscosity and the distribution of pebble species, which yield a diversity of planetary cores. With accretion of multiple pebble species, planetary cores can grow very fast, reaching over 30–40 ME in mass. Potential cores of cold gas giants were able to form from embryos initially implanted as far as 50 au. Our results suggest that accretion of multispecies pebbles could explain: the estimated 25–45 ME heavy element abundance inside Jupiter’s core; the massive cores of extrasolar planets; the disc rings and gaps at wider orbits; and the early and rapid formation of planetary bodies.

Demonstrating the Relationship between the Colour and Heavy Element Abundance of Globular Clusters

Extragalactic globular clusters are viewed as single points of light, as the density of their stars make them individually indiscernible. The aim of this study was to find a correlation between the integrated colour of globular star clusters and the metallicity of their individual stars. This was accomplished by using the colour magnitudes and metallicities of individual stars from 11 cluster models based on work from Girardi et al. Integrated colour-metallicity diagrams found the relationship between clusters to be an increasing two-step linear function for each of the six colour ratios examined. To validate the findings, the F475W-F814W relationship was applied to integrated colour data of 5557 clusters from the real galaxy NGC 6166. Histograms taken of the colour and metallicity both showed non-gaussian distributions. Bimodal gaussian fits were applied to both and found that each exhibited the presence of subpopulations: one metal-poor (μ = -1.59), and one metal-rich (μ = -0.41). This suggests the occurrence of galactic mergers with NGC 6166 to create the population structure of clusters that is currently seen.

Observational Evidence Points at AGB Stars as Possible Progenitors of CEMP-s and CEMP-r/s Stars*

Abstract The origin of enhanced abundance of heavy elements observed in the surface chemical composition of carbon-enhanced metal-poor (CEMP) stars still remains poorly understood. Here, we present detailed abundance analysis of seven CEMP stars based on high-resolution (R ∼ 50,000) spectra that reveal enough evidence of asymptotic giant branch (AGB) stars being possible progenitors for these objects. For the objects HE 0110−0406, HE 1425−2052, and HE 1428−1950, we present for the first time a detailed abundance analysis. Our sample is found to consist of one metal-poor ([Fe/H] < −1.0) and six very metal-poor ([Fe/H] < −2.0) stars with enhanced carbon and neutron-capture elements. We have critically analyzed the observed abundance ratios of [O/Fe], [Sr/Ba], and [hs/ls] and examined the possibility of AGB stars being possible progenitors. The abundance of oxygen estimated in the program stars is characteristic of AGB progenitors except for HE 1429−0551 and HE 1447+0102. The estimated values of [Sr/Ba] and [hs/ls] ratios also support AGB stars as possible progenitors. The locations of the program stars in the absolute carbon abundance A(C) versus [Fe/H] diagram, along with the Group I objects, hint at the binary nature of the object. We have studied the chemical enrichment histories of the program stars based on abundance ratios [Mg/C], [Sc/Mn], and [C/Cr]. Using [C/N] and 12C/13C ratios, we have examined whether any internal mixing had modified their surface chemical compositions. Kinematic analysis shows that the objects HE 0110−0406 and HE 1447+0102 are thick-disk objects and the remaining five objects belong to the halo population of the Galaxy.

Formation, diffusion, and accreting pollution of DB white dwarfs

Context. Over 1500 DBZ or DZ white dwarfs (WDs) have been observed so far, and polluted atmospheres with metal elements have been found among these WDs. The surface heavy element abundances of known DBZ or DZ WDs show an evolutionary sequence. Cooling, diffusion, and accretion are important physical processes in WD evolution which can alter the element abundances of the WD surface. Aims. Using the stellar evolutionary code, we investigated the DB WD formation and the effects of input parameters −, including the mixing length parameter (αMLT), thermohaline mixing efficiency (αth), and the metallicity (Z) −, on the structures of these DB WDs. The impacts of the convective zone mass (Mcvz), cooling timescales, diffusive timescales (τdiff), and the mass-accretion rate (Ṁa) on the element abundances of the WDs’ surfaces are discussed. By comparing the theoretical model results with observations, we try to understand the evolutionary sequence of the heavy element abundance on DBZ WD surfaces. Methods. By using Modules for Experiments in Stellar Evolution, we created DB WDs, and simulated the element diffusion due to high gravitational fields and the metal-rich material accretion coming from the planet disrupted by the WD. Then, we calculated the element abundances of these DB WDs for a further comparison with observations. Results. In our models, the input parameters (αMLT, αth, and Z) have a very weak effect on DB WD structures, including interior temperatures, chemical profiles, and convective zones. They hardly affect the evolution of the heavy elements on the surface of DB WDs. The mass-accretion rate and the effective temperature of DB WDs determine the abundances of heavy elements. The evolutionary sequence of the Ca element for about 1500 observed DB or DBZ WDs cannot be explained by the model with a constant mass-accretion rate, but it is very consistent with the model in which the mass-accretion rate decreases by one power law when Teff > 10 kK and it slightly increases by another power law when Teff < 10 kK. Conclusions. The observed DB WD evolutionary sequence of heavy element abundances originates from WD cooling and the change in the mass-accretion rate.

UVES analysis of red giants in the bulge globular cluster NGC 6522

Context. NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H] ~ −1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy. Aims. The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r-process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na–Al, Na–N, and Mg–Al correlations, while we cannot identify the Na–O anti-correlation from our data. Methods. High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe I and Fe II lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out. Results. The present analysis combined with previous UVES results gives a mean radial velocity of vrhel = −15.62±7.7 km s−1 and a metallicity of [Fe/H] = −1.05 ± 0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe] = +0.38, [Mg/Fe] = ≈+0.28, [Si/Fe] ≈ +0.19, and [Ca/Fe] ≈ +0.13, together with the iron-peak element [Ti/Fe] ≈ +0.13, and the r-process element [Eu/Fe] = +0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and −0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances.

Fifty Years of 3He-Rich Events

The early 1970s saw a new and surprising feature in the composition of solar energetic particles (SEPs), resonant enhancements up to 10,000-fold in the ratio 3He/4He that could even make 3He dominant over H in rare events. It was soon learned that these events also had enhancements in the abundances of heavier elements, such as a factor of ∼10 enhancements in Fe/O, which was later seen to be part of a smooth increase in enhancements vs. mass-to-charge ratio A/Q from H to Pb, rising by a factor of ∼1000. These events were also associated with streaming 10–100 keV electrons that produce type III radio bursts. In recent years we have found these “impulsive” SEP events to be accelerated in islands of magnetic reconnection from plasma temperatures of 2–3 MK on open field lines in solar jets. Similar reconnection on closed loops traps the energy of the particles to produce hot (>10 MK), bright flares. Sometimes impulsive SEP intensities are boosted by shock waves when the jets launch fast coronal mass ejections. No single theory yet explains both the sharp resonance in 3He and the smooth increase up to heavier elements; two processes seem to occur. Sometimes the efficient acceleration even exhausts the rare 3He in the source region, limiting its fluence.

NGC 1261: An r-process enhanced globular cluster from the Gaia-Enceladus event

Our Milky Way (MW) has witnessed a series of major accretion events in the past. One of the later additions, the Gaia-Enceladus merger, has contributed a considerable mass to the inner Galaxy, but also generously donated to the outer halo. So far, associations with present-day MW globular clusters (GCs) have been chiefly based on their kinematics and ages. In this work, we present a chemical abundance study of the outer halo (RGC ∼ 18 kpc) GC NGC 1261, which has been suggested to be an accreted object based on its younger age. We measured 31 species of 29 elements in two stars from high-resolution Magellan/MIKE spectra and find that the cluster is moderately metal poor, at [Fe/H] = −1.26, with a low scatter of 0.02 dex. NGC 1261 is moderately α-enhanced to the 0.3 dex level. While from the small sample alone it is difficult to assert any abundance correlations, the light elements Na, O, Mg, and Al differ significantly between the two stars in contrast to the majority of other elements with smaller scatter; this argues in favor of multiple generations of stars coexisting in this GC. Intriguingly for its metallicity, NGC 1261 shows heavy element abundances that are consistent with r-process nucleosynthesis and we discuss their origin in various sites. In particular the Eu overabundance quantitatively suggests that one single r-process event, such as a neutron-star neutron-star merger or a rare kind of supernova, can be responsible for the stellar enhancement or even the enrichment of the cluster with the excess r material. Its heavy element pattern makes NGC 1261 resemble the moderately enhanced r-I stars that are commonly found in the halo and have been detected in Gaia-Enceladus as well. Therefore, combining all kinematical, age, and chemical evidence we conclude that NGC 1261 is a chemically intriguing GC that was born in the Gaia-Enceladus galaxy and has been subsequently accreted into the MW halo.

APOGEE-2S Discovery of Light- and Heavy-element Abundance Correlations in the Bulge Globular Cluster NGC 6380

Abstract We derive abundance ratios for nine stars in the relatively high-metallicity bulge globular cluster NGC 6380. We find a mean cluster metallicity between [Fe/H] = −0.80 and −0.73, with no clear evidence for a variation in iron abundances beyond the observational errors. Stars with strongly enhanced [N/Fe] abundance ratios populate the cluster and are anticorrelated with [C/Fe], trends that are considered a signal of the multiple-population phenomenon in this cluster. We detect an apparent intrinsic star-to-star spread (≳0.27 dex) in the slow neutron-capture process element (s-element) Ce ii. Moreover, the [Ce/Fe] abundance ratio exhibits a likely correlation with [N/Fe], and a somewhat weaker correlation with [Al/Fe]. If confirmed, NGC 6380 could be the first high-metallicity globular cluster where a N–Ce correlation is detected. Furthermore, this correlation suggests that Ce may also be an element involved in the multiple-population phenomenon. Currently, a consensus interpretation for the origin of the this apparent N–Ce correlation in high-metallicity clusters is lacking. We tentatively suggest that it could be reproduced by different channels—low-mass asymptotic giant branch stars in the high-metallicity regime or fast-rotating massive stars (“spinstars”), due to the rotational mixing. It may also be the cumulative effect of several pollution events including the occurrence of peculiar stars. Our findings should guide stellar nucleosynthesis models, in order to understand the reasons for its apparent exclusivity in relatively high-metallicity globular clusters.

In-depth analysis of evolving binary systems that produce nova eruptions

ABSTRACT This study is the direct continuation of a previous work performed by Hillman et al., where they used their feedback dominated numerical simulations to model the evolution of four initial models with white dwarf (WD) masses of 0.7 and $1.0\, \mathrm{M}_\odot$ and red dwarf (RD) masses of 0.45 and $0.7\, \mathrm{M}_\odot$ from first Roche lobe contact of the donor RD, over a few times 109 yr, until the RD was eroded down to below $0.1\, \mathrm{M}_\odot$. This study presents an in-depth analysis of their four models complimented by three models with a higher WD mass of $1.25\, \mathrm{M}_\odot$, one of which comprises an oxygen-neon (ONe) core. Common features were found for all seven models on a secular time-scale as well as on a cyclic time-scale. On the other hand, certain features were found that are strongly dependent either on the WD or the RD mass but are indifferent to the other of the two. Additionally, a model with a WD composed of an ONe core was compared with its corresponding carbon oxygen (CO) core WD model and found to have a significant impact on the heavy element abundances in the ejecta composition.

S stars and s-process in the Gaia era

Context. S stars are late-type giants that are transition objects between M-type stars and carbon stars on the asymptotic giant branch (AGB). They are classified into two types: intrinsic or extrinsic, based on the presence or absence of technetium (Tc). The Tc-rich or intrinsic S stars are thermally pulsing (TP-)AGB stars internally producing s-process elements (including Tc) that are brought to their surface via the third dredge-up (TDU). The Tc-poor or extrinsic S stars gained their s-process overabundances via the accretion of s-process-rich material from an AGB companion that has since turned into a dim white dwarf. Aims. Our goal is to investigate the evolutionary status of Tc-rich S stars by locating them in a Hertzsprung-Russell (HR) diagram using the results of Gaia Early Data Release 3 (EDR3). We combine the current sample of 13 Tc-rich stars with our previous studies of 10 Tc-rich stars to determine the observational onset of the TDU in the metallicity range [−0.7; 0]. We also compare our abundance determinations with dedicated AGB nucleosynthesis predictions. Methods. We derived the stellar parameters using an iterative tool that combines HERMES high-resolution spectra, accurate Gaia EDR3 parallaxes, stellar evolution models, and tailored MARCS model atmospheres for S-type stars. Using these stellar parameters, we determined the heavy-element abundances by line synthesis. Results. In the HR diagram, the intrinsic S stars are located at higher luminosities than the predicted onset of the TDU. These findings are consistent with Tc-rich S stars being genuine TP-AGB stars. The comparison of the derived s-process abundance profiles of our intrinsic S stars with the nucleosynthesis predictions provide an overall good agreement. Stars with highest [s/Fe] tend to have the highest C/O ratios.