Li Abundance Research Articles

Hamilton Echelle Spectrograph Observations of Solar Analog Field Stars: Lithium Abundance and Activity

We measured lithium (Li) abundance and instantaneous chromospheric Ca ii HK activity in Hamilton Echelle Spectrograph observations of 211 solar analog field stars, with one objective being potential identification of grand minimum candidates for ongoing multiyear observation. At the zero-age main sequence, Li abundance for a typical late-type dwarf begins at the local interstellar medium abundance and over the main sequence lifetime is steadily depleted by convection at a rate dependent on details of the star’s convection and mixing processes. Our Li abundance measurements show an overall decrease in Li abundance with age and effective temperature, consistent with earlier surveys. In our activity measurements, 41 stars show log R′HK ≤ −5.0, which can be considered very inactive. Of the very inactive stars closest to solar effective temperature, 24 show Li abundances within the range typically observed for midlife Sun-like stars. Another three show very low Li abundance, which, combined with the low activity, suggest an older main sequence star or a slightly evolved star. We suggest that the combination of relatively undepleted Li and instantaneous very low activity might make these stars promising candidates for long time-series observations to determine if they are in a grand minimum state. The Hamilton Echelle Spectrograph observations are publicly available for download and are potentially useful for a variety of survey tasks involving Sun-like stars.

Proton ingestion in asymptotic giant branch stars as a possible explanation for J-type stars and AB2 grains

J-type stars are a subclass of carbon stars that are generally Li-rich, not enriched in s-elements, and have low 12C/13C ratios. They were suggested to be the manufacturers of the pre-solar grains of type AB2 (having low 12C/13C and supersolar 14N/15N). In this Letter, we investigate the possibility that J-type stars are early asymptotic giant branch (AGB) stars that experienced a proton ingestion event (PIE). We used the stellar evolution code STAREVOL to compute AGB stellar models with initial masses of 1, 2, and 3 and metallicities Fe/H $= -0.5$ and 0.0. We included overshooting above the thermal pulse and used a network of 1160 nuclei coupled to the transport equations. The outputs of these models were compared to observations of J-type stars and AB2 grains. In solar-metallicity AGB stars, PIEs can be triggered if a sufficiently high overshoot is considered. These events lead to low 12C/13C ratios, high Li abundances, and no enrichment in s-elements. We find that the $2-3$ AGB models experiencing a PIE can account for most of the observational features of J-type stars and AB2 grains. The remaining tensions between models and observations are (1) the low 14N/15N ratio of some AB2 grains and of 2 out of 13 J-type stars, (2) the high 26Al/27Al of some AB2 grains, and (3) the J-type stars with A(Li) $<2$. Extra mixing mechanisms can alleviate some of these tensions, such as thermohaline or rotation. This work highlights a possible match between AGB stellar models that undergo a PIE and J-type stars and AB2 grains. To account for other types of carbon stars, such as N-type stars, PIEs should only develop in a fraction of solar-metallicity AGB stars. Additional work is needed to assess how the occurrence of PIEs depends on mixing parameters and initial conditions, and therefore to further confirm or exclude the proposed scenario.

Evolution of lithium in the disc of the Galaxy and the role of novae

Lithium plays a crucial role in probing stellar physics, stellar and primordial nucleosynthesis, and the chemical evolution of the Galaxy. Stars are considered to be the main source of Li, yet the identity of its primary stellar producer has long been a matter of debate. In light of recent theoretical and observational results, we investigate in this study the role of two candidate sources of Li enrichment in the Milky Way, namely asymptotic giant branch (AGB) stars and, in particular, novae. We utilised a one-zone Galactic chemical evolution (GCE) model to assess the viability of AGB stars and novae as stellar sources of Li. We used recent theoretical Li yields for AGB stars, while for novae we adopted observationally inferred Li yields and recently derived delay time distributions (DTDs). Subsequently, we extended our analysis by using a multi-zone model with radial migration to investigate spatial variations in the evolution of Li across the Milky Way disc and compared the results with observational data for field stars and open clusters. Our analysis shows that AGB stars clearly fail to reproduce the meteoritic Li abundance. In contrast, novae appear as promising candidates within the adopted framework, allowing us to quantify the contribution of each Li source at the Sun's formation and today. Our multi-zone model reveals the role of the differences in the DTDs of Type Ia supernovae and novae in shaping the evolution of Li in the various galactic zones. Its results are in fair agreement with the observational data for most open clusters, but small discrepancies appear in the outer disc.

Chemical Evolution of R-process Elements in Stars (CERES). II. The impact of stellar evolution and rotation on light and heavy elements

Carbon, nitrogen, and oxygen are the most abundant elements throughout the universe, after hydrogen and helium. Studying these elements in low-metallicity stars can provide crucial information on the chemical composition in the early Galaxy and possible internal mixing processes that can alter the surface composition of the stars. This work aims to investigate the chemical abundance patterns for CNO elements and Li in a homogeneously analyzed sample of 52 metal-poor halo giant stars. From these results, we have been able to determine whether internal mixing processes have taken place in these stars. We used high-resolution spectra with a high signal-to-noise ratio (S/N) to carry out a spectral synthesis to derive detailed C, N, O, and Li abundances for a sample of stars with metallicities in the range of$-$3.58 leq Fe/H leq $-$1.79\,dex. Our study was based on the assumption of one-dimensional (1D) local thermodynamic equilibrium (LTE) atmospheres. Based on carbon and nitrogen abundances, we investigated the deep mixing taking place within stars along the red giant branch (RGB). The individual abundances of carbon decrease towards the upper RGB while nitrogen shows an increasing trend, indicating that carbon has been converted into nitrogen. No signatures of ON-cycle processed material were found for the stars in our sample. We computed a set of galactic chemical evolution (GCE) models, implementing different sets of massive star yields, both with and without including the effects of stellar rotation on nucleosynthesis. We confirm that stellar rotation is necessary to explain the highest N/Fe and N/O ratios observed in unmixed halo stars. The predicted level of N enhancement varies sensibly in dependence of the specific set of yields that are adopted. For stars with stellar parameters similar to those of our sample, heavy elements such as Sr, Y, and Zr appear to have unchanged abundances despite the stellar evolution mixing processes. The unmixed RGB stars provide very useful constraints on chemical evolution models of the Galaxy. As they are more luminous than unevolved (main sequence and turnoff) stars, they also allow for stars to be probed at greater distances. The stellar CN-cycle clearly changes the atmospheric abundances of the lighter elements, but no changes were detected with respect to the heavy elements.

Are lithium-rich giants binaries? A radial velocity variability analysis of 1400 giants

Context. The existence of low-mass giants with large amounts of lithium (Li) in their surfaces has challenged stellar evolution for decades. One of the possibilities usually discussed in the literature to explain these Li-rich giants involves the interaction with a close binary companion, a scenario that predicts that, when compared against their non-enriched counterparts, Li-rich giants should preferentially be found as part of binary systems. Aims. We aim to assemble the largest possible sample of low-mass giants with well-measured Li abundances, to determine with high statistical significance the close binary fractions of Li-rich and Li-normal giants, and thus test the binary interaction scenario for the emergence of Li-rich giants. Methods. We developed a method that uses radial velocities (RVs) at three different epochs to quantify the degree of RV variability, which we used as a proxy for the presence of a close binary companion. The method was tested and calibrated against samples of known RV standard stars and known spectroscopic binaries. We then assembled a sample of 1418 giants with available RVs from RAVE, GALAH, and Gaia, as well as stellar parameters and Li abundances from GALAH, to which we applied our variability classification. We could determine an evolutionary state for 1030 of these giants. We also compared the results of our RV variability analysis with binarity indicators from the Gaia mission. Results. When applying our methodology to the control samples, we found that the accuracy of the classification is controlled by the precision of the RVs used in the analysis. For the set of RVs available for the giants, this accuracy is 80–85%. Consistent with seismic studies, the resulting sample of giants contains a fraction of Li-rich objects in the red clump (RC) that is twice as large as that in the first ascent red giant branch (RGB). Among RC giants, the fractions of Li-rich objects with a high RV variability and with no RV variability are the same as those for Li-normal objects, but we find some evidence that these fractions may be different for giants in the first-ascent RGB. Analysis of binary indicators in Gaia DR3 shows a smaller fraction of binary giants than our criteria, but no relation can be seen between Li enrichment and binarity either. Conclusions. Our RV variability analysis indicates that there is no preference for Li-rich giants in the RC to be part of binary systems, thus arguing against a binary interaction scenario for the genesis of the bulk of Li-rich giants at that evolutionary stage. On the other hand, Li-rich giants in the RGB appear to have a small but measurable preference for having close companions, something that deserves further scrutiny with more and better data. Additional measurements of the RVs of these giants at a higher RV precision would greatly help in confirming and more robustly quantifying these results.

A coherent view of Li depletion and angular momentum transport to explain the Li plateau – from Population II to Population I stars

Context. The discrepancy between the predictions of Big Bang nucleosynthesis and the lithium abundance observed in the oldest stars of our Galaxy, known as the cosmological lithium problem, has long been regarded as a challenge to the fields of both cosmology and astrophysics. Aims. In light of recent theoretical advances concerning the transport of chemicals and angular momentum in Population I low-mass stars, we re-examine the stellar depletion hypothesis to explain the lithium plateau, which spans a wide range of metallicities over a specific range of stellar effective temperature. Methods. We computed stellar evolution models with the code STAREVOL, including the same input physics that enable self-consistent reproduction of the Li depletion in the Sun and stars in open clusters, while accounting for internal rotation consistent with asteroseismic constraints. In addition to atomic diffusion and parametric turbulence, which were considered in previous studies of Li depletion along the plateau, our models include rotation-induced hydrodynamical processes and additional parametric viscosity for the transport of angular momentum as well as penetrative convection with a rotational dependence, and magnetic braking. Results. As in the case of Pop I stars, the mixing obtained with the current prescriptions for vertical and horizontal shear turbulence induced by rotation is insufficient to reproduce the Li constraints, and parametric turbulence is required. Even if the nature of the turbulence has yet to be identified, we show that the compactness of Pop II low-mass dwarf stars shall naturally lead to similar Li depletion over a large domain in the [Fe/H]–Teff plane, resulting in a plateau with little dispersion. We calibrated the efficiency of the turbulence to fit the abundance of Li in Pop II stars selected from the GALAH DR3 spectroscopic survey and from an homogeneous reanalysis of abundances from the literature. This calibration also enables the reproduction of lithium and magnesium trends in post-turnoff stars of the globular cluster NGC 6752. The same stellar structure considerations consistently explain the observed change of Li depletion and the dispersion regime for [Fe/H] above −1.5 dex, that is, at the transition in metallicity between Pop II to Pop I stars. Conclusions. Our results provide new constraints to the physical processes that transport chemicals and angular momentum in stellar interiors. They offer a comprehensive way to reproduce the observed Li patterns in low-mass dwarf stars across the entire Galactic metallicity range covered by spectroscopic surveys, including the most Fe-poor regime, as supported by the Li value in the non-CEMP star that lies on the plateau at [Fe/H] below −5.8 dex. Our careful analysis of the other very metal-poor stars with lower Li abundances supports the environmental origin of the so-called meltdown regime. Finally, the expected plateau-to-scatter transition pattern further supports the stellar solution to the cosmological problem.

Li enrichment in peridotites and chromitites tracks mantle-crust interaction

The ultramafic massifs of the Serranía de Ronda in southern Spain are the Earth's largest exposures of subcontinental lithospheric mantle (SCLM) peridotites (∼450 km2). These ultramafic massifs experienced asthenosphere melt percolation during their crustal emplacement. Mixing of these mafic melts with anatectic melts and fluids led to the formation of a world's unique Ni-arsenide-rich chromitite ores (hereafter CrNi ores) associated with orthopyroxenite and/or cordieritite (i.e., > 90 % volume of cordierite) hosted within the peridotites. This study uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate the Li in rock-forming minerals of peridotite and CrNi ores to evaluate the role of Li as crustal tracer. Clinopyroxene crystallized from asthenospheric melts exhibits high Li contents (up to 8.5 ppm), exceeding the average values of the upper mantle (∼ 0.7 ppm), whereas orthopyroxene, olivine, and Cr-spinel from peridotite are mostly Li-depleted. In contrast, all rock-forming minerals of CrNi ores have abnormally high Li contents, displaying an overall Li enrichment trend toward the external parts of ultramafic massifs, on the way to the crustal rocks. This trend is evident in Cr-spinel from the CrNi ores, which display 6.9–7.9 ppm Li in the deepest portions of the massif (Arroyo de la Cala CrNi ore) up to 1.4–8.5 ppm in the shallowest part (La Gallega CrNi ore), as well as in orthopyroxenes that have 31.3–44.7 ppm Li in Arroyo de la Cala, and 45.1–51.4 ppm Li in La Gallega. Cordierite is present only in the CrNi ores situated in the external part of the ultramafic massifs, exhibiting 113.15–160.82 ppm Li in the Barranco de las Acedías CrNi ore and 36.5–60.5 ppm Li in La Gallega CrNi ore. Similarly to Li, LREE, fluid-mobile elements (K, Rb, Ba), and Sr in orthopyroxenes from the CrNi ores display enrichment from the inner to the outer parts of the ultramafic massif. These geochemical variations suggest that Li enrichment in CrNi ores and host peridotites was a twofold process: (1) asthenospheric melt percolation slightly increased Li abundances in the SCLM peridotites by modal and cryptic metasomatism involving clinopyroxene; (2) additional infiltration of Li-bearing crustally-derived fluids during the intracrustal emplacement of the mantle section boosted the Li contents of minerals in the CrNi ores. Our results highlight that Li may effectively track the interaction of the SCLM with crustal components.

Discovery of a Metal-poor Red Giant Star with the Highest Ultralithium Enhancement

We present the discovery of 2MASS J05241392−0336543 (hereafter J0524−0336), a very metal-poor ([Fe/H] = −2.43 ± 0.16), highly r-process-enhanced ([Eu/Fe] = +1.34 ± 0.10) Milky Way halo field red giant star, with an ultrahigh Li abundance of A(Li, 3D, NLTE) = 6.15 ± 0.25 and [Li/Fe] = +7.64 ± 0.25, respectively. This makes J0524−0336 the most lithium-enhanced giant star discovered to date. We present a detailed analysis of the star’s atmospheric stellar parameters and chemical abundance determinations. Additionally, we detect indications of infrared excess, as well as observe variable emission in the wings of the Hα absorption line across multiple epochs, indicative of a potential enhanced mass-loss event with possible outflows. Our analysis reveals that J0524−0336 lies either between the bump and the tip of the red giant branch (RGB), or on the early asymptotic giant branch (e-AGB). We investigate the possible sources of lithium enrichment in J0524−0336, including both internal and external sources. Based on current models and on the observational evidence we have collected, our study shows that J0524−0336 may be undergoing the so-called lithium flash that is expected to occur in low-mass stars when they reach the RGB bump and/or the e-AGB.

All Inorganic Scintillating Fiber for Thermal Neutron Detection

AbstractThermal neutron detection with scintillating fibers has excellent scientific and technological potential for remote and spatially resolved detection. However, most fibers are polymers, and developing all‐inorganic scintillating fibers remains a significant challenge. Herein, all‐inorganic scintillating fibers and prototype neutron detection devices are successfully constructed for neutron detection. The scintillating fibers with a perfect waveguide configuration and tunable size have been fabricated through the melt‐in‐tube method. The interactions between the thermal neutron and scintillating fiber have been theoretically analyzed. The dependence of the neutron absorption ability on the core diameter, cladding thickness, and 6Li abundance has been investigated. Guided by the above experimental and theoretical results, the configuration of the scintillating fiber and the corresponding neutron detection prototype device has been built. Its practical application for neutron detection has been demonstrated, and importantly, the single thermal neutron event can be successfully monitored. The device shows great promise for neutron detection applications in special scenarios such as tiny space and electromagnetic interference environments.

The true nature of HE 0057-5959, the most metal-poor, Li-rich star

The Li-rich stars are a class of rare objects with a surface lithium abundance, A(Li), that exceeds that of other stars in the same evolutionary stage. The origin of these stars is still debated, and valuable routes to look at include the Cameron-Fowler mechanism, a mass-transfer process in a binary system, or the engulfment of rocky planets or brown dwarfs. Metal-poor ([Fe/H]<−1 dex) stars are only a small fraction of the entire population of Li-rich stars. We observed the metal-poor ([Fe/H]=−3.95±0.11 dex) giant star HE 0057–5959 with MIKE at the Magellan Telescope, deriving A(Li)NLTE=+2.09±0.07 dex. Such an Li abundance is significantly higher, by about 1 dex, than that of other stars at the same evolutionary stage. A previous analysis of the same target suggested that its high A(Li) reflects an ongoing first-dredge-up process. We revised the nature of HE 0057-5959 by comparing its stellar parameters and A(Li) with appropriate stellar evolution models describing Li depletion due to the deepening of the convective envelope. This comparison rules out that HE 0057-5959 is caught during its first dredge-up, the latter having already ended according to the parameters of this star. Its A(Li), remarkably higher than the typical lithium plateau drawn by similar giant stars, demonstrates that HE 0057-5959 joins the class of the rare metal-poor, Li-rich stars. HE 0057-5959 is the most metal-poor, Li-rich star discovered so far. We considered different scenarios to explain this star also comparing it with the other metal-poor, Li-rich stars. No internal mixing able to activate the Cameron-Fowler mechanism is known for metal-poor stars at this evolutionary stage. The engulfment of planets is also disfavoured because such metal-poor stars should not host planets. Finally, HE 0057-5959 is one of the most Na-rich among the Li-rich stars, and we found that a strong excess of Na abundance is common to all three Li-rich stars with [Fe/H]<–3 dex. This finding could support the scenario of mass transfer from a massive companion star (able to simultaneously produce large amounts of both elements) in a binary system, even if we found no evidence of radial velocity variations.

Primordial Lithium from Globular Cluster Turnoff Stars: M13 and M71

During Big Bang nucleosynthesis (BBN) in the first 15 minutes of the Universe, some 7Li was created along with isotopes of H and He. The determination of that primordial value of Li can help constrain the conditions at that time. The oldest stars with known ages can be found in globular clusters which have well-determined ages through stellar evolution models. High-resolution spectra of Li have been obtained with the Keck I Telescope and HIRES in several unevolved stars in the clusters M13 and M71 with V magnitudes of 17.6–17.9. Abundances of Li have been determined with spectrum synthesis techniques and show a range of a factor of 4. We attribute that spread to differences in initial angular momentum resulting in different amounts of spin-down, related mixing, and destruction of Li. Our results are compared with similar results for main-sequence and turnoff stars in other globular clusters. The range in age of these clusters is 11.2–14.2 Gyr for an age span of 3 Gyr. These clusters range in [Fe/H] from −0.75 to −2.24 corresponding to a factor of 30 in metallicity. The maximum in the Li abundance for these unevolved stars in all eight clusters is the same corresponding to Li/H = 3.16 × 10−10, while the predicted Li abundance, based on the deuterium abundance and the BBN predictions, is 5.24 × 10−10.

The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals

Context. Despite the large number of studies focused on the characterisation of Li-rich stars and understanding the mechanisms leading to such enrichment, their origin remains a mystery. Aims. Magnetic activity, particularly the phenomena usually associated with it (e.g. spots and plages), and the Li abundance (A(Li)) of stars, are in general thought to be connected. As of today, however, just how they are connected is unclear. In this work, we study a sample of young but evolved intermediate-mass red giants that are inhabitants of open clusters where planets have been searched for. Our aim is to use radial velocity (RV) and stellar activity indicator signals to look for relations between Li abundances and stellar activity or variability. Methods. We explored how the standard deviation (STD), peak-to-peak amplitude (PTP), mean, and median of typical stellar activity indicators (BIS, FWHM, Teff, and Hα index) change as a function of the Li content of 82 red giants. Furthermore, we computed weighted Pearson correlation coefficients (ρw) between time series of RV measurements and the stellar activity indicators for the stars in our sample. To aid our results, we also studied generalized Lomb–Scargle periodograms (GLSP) to capture possible significant periodic temporal variations in our data. Results. Our analysis indicates that the STD and PTP of BIS and FWHM, the mean and median of the Hα index, and υ sin(i) increase exponentially with A(Li) in our sample of red giants. Significant temporal variations and correlations between RVs and activity indicators also tend to be found preferentially for stars where high A(Li) is observed. Most of the Li-rich stars in our sample either show strong correlations of RV with at least one of the stellar activity indicators or reveal significant periodic temporal variations in their GLSPs of stellar activity indicators that are consistent with those found for RV.

Study of a Red Clump Giant, KIC 11087027, with High Rotation and Strong Infrared Excess—Evidence of Tidal Interaction for High Lithium Abundance

This Letter presents results from Kepler photometric light curves and a high-resolution spectroscopic study of a super-Li-rich giant KIC11087027. Using the light-curve analysis, we measured the star’s rotational period P rot = 30.4 ± 0.1 days, which translates to rotational velocity V rot = 19.5 ± 1.7 km s−1. The star’s location in the Hertzsprung–Russell diagram, derived values of 12C/13C = 7 ± 1 and [C/N] = −0.95 ± 0.2, and the inferred asteroseismic parameters from secondary calibration based on spectra suggest the star is a low-mass red clump giant in the He-core burning phase. Using Gaia data, we found evidence of variation in radial velocity and proper motion, indicative of presence of an unresolved binary. The large V rot is probably a result of tidal synchronization combined with the aftereffects of He flash, in which the size of the star is reduced significantly. The simultaneous presence of features like high rotation, very high Li abundance, strong dust shell, and strong flares in a single star is relatively uncommon, suggesting that the star experiencing tidal synchronization has recently undergone He flash. The results pose a question whether the binary interaction, hence the high rotation, is a prerequisite for the dredging up of the high amounts of Li from the interior to the photosphere during or immediately after the He-flash event.

Evolution of magma compositions and phosphorus availability in early Earth’s crust: New constraints from zircon-melt partitioning experiments

Abstract Zircons are the oldest remaining witnesses of Earth’s near-surface processes, and conditions in the Hadean and Archaean crust are derived predominantly from their trace element and isotopic compositions. However, quantitative assessment of element and isotope partitioning between zircon and melt remains incomplete. We experimentally determined the effect of phosphorus (P) abundance on zircon-melt partition coefficients of Al (DAl), Li (DLi), and P (DP). Results indicate that P content has opposite effects on DAl and DLi, whereas the partitioning of P itself and other trace elements is independent of P abundance. Parametrization of our results yields new assessments of the aluminum saturation index (ASI) and P and Li contents of Hadean magmas. Magma ASI values are ~0.5 lower than previously thought and consistently remain below 1 during the first ~1 Ga of Earth evolution, suggesting involvement of only igneous protoliths. First peraluminous (ASI > 1) melts do not appear until ca. 3.6 Ga, supporting the hypothesis that a transition from a tectonic style dominated by vertical motion to horizontal tectonics accompanied by partial melting of sediments did not occur before that time. New calculated magma Li concentrations for young zircons are in much better agreement with the continental crust Li abundance. Average calculated Archaean and Hadean magma Li concentrations are unrealistically large (>1000 ppm), suggesting that Li in zircons formed before 2 Ga is not primary. Calculated magma P abundances are uniform (~1900 ± 400 ppm) throughout Earth history, suggesting sufficient crustal P was available throughout the Hadean to support the origin of life.

Extragalactic 85Rb/87Rb and 6Li/ ^7Li ratios in the Small Magellanic Cloud

The line of sight toward Sk 143 (AzV 456), an O9.5 Ib star in the Small Magellanic Cloud (SMC), shows significant absorption from neutral atoms and molecules. We report a new study of this line of sight by means of high-resolution spectra obtained with the ESPRESSO spectrograph at the VLT of ESO. The absorption from neutral and ionized species is well characterized by a single component at v$_ hel $ approx +132 that was modeled with the ASTROCOOK code. The rubidium Rb I 780.0 nm line is detected for the first time outside the Galaxy, and we derive Rb/H = -1.86 pm 0.09. As a result of the high resolution, the 85Rb and 87Rb isotope lines are also exceptionally well resolved. The 85Rb/87Rb isotope ratio is 0.46, which is opposite of the meteoritic value of 2.43. This implies that Rb is made through a dominant contribution of the $r$-process, which is dominant for the 87Rb isotope. We also confirm the presence of 670.7 nm and set a limit on the isotopic ratio of $^6$Li/$^7Li$ < 0.1. The dominance of the 87Rb isotope implies that Rb is made through a dominant contribution of the $r$-process. At the low metallicity of the cloud of Zn/H = -1.28 pm 0.09 , neutron rich material may have occurred in rotating metal-poor massive stars. Moreover, the low metallicity of the cloud leads to an absolute Li abundance of A($^7$Li) approx 2.2, which differs from the expectation from big bang nucleosynthesis. Because the gas-phase abundance is not affected by stellar depletion, the burning of Li inside the halo stars is probably not the solution for the cosmological $^7$Li problem.

Constraining MeV to 10 GeV Majorons by big bang nucleosynthesis

We estimate the big bang nucleosynthesis (BBN) constraint on the majoron in the mass range between 1 MeV to 10 GeV which dominantly decays into the standard model neutrinos. When the Majoron lifetime is shorter than 1 sec, the injected neutrinos mainly heat up background plasma, which alters the relation between photon temperature and background neutrino temperature. For a lifetime longer than 1 sec, most of the injected neutrinos directly contribute to the protons-to-neutrons conversion. In both cases, deuterium and helium abundances are enhanced, while the constraint from the deuterium is stronger than that from the helium. Li7 abundance gets decreased as a consequence of additional neutrons, but the parameter range that fits the observed Li7 abundance is excluded by the deuterium constraint. We also estimate other cosmological constraints and compare them with the BBN bound. Published by the American Physical Society 2024

Slow 7Be and the primordial 7Li abundance

The cross sections of neutron-induced nuclear reactions are commonly large at low energies. Given this feature, the 7Be(n, p)7Li process with slow 7Be is studied in connection with the cosmological lithium problem. An idea is tested whether slow (non-Maxwellian) 7Be born in the radiative capture 3He(α, γ)7Be reaction can boost the 7Be(n, p)7Li(p, α)α mechanism of 7Li burn-up in the early universe, reducing the amount of primordial 7Li. The rate of this sequential process is examined and its effect on the 7Li abundance is clarified. In the absence of 7Be thermalization in the primordial plasma, the above mechanism can decrease 7Li/H by several percent, leaving unchanged the abundances of D and 4He which are consistent with observations. However, taking into account the 7Be thermalization due to scattering off electrons, positrons, nuclei, and photons radically suppresses the effect. It is found that the typical thermalization time of 7Be is less than 10−5 s, while the fraction of non-Maxwellian particles in the 7Be component is at most 2 × 10−7. Under this condition, the corresponding impact on 7Li/H is estimated to be no more than 10−5%.

Slab melting boosts the mantle wedge contribution to Li-rich magmas

The lithium cycling in the supra-subduction mantle wedge is crucial for understanding the generation of Li-rich magmas that may potentially source ore deposition in continental arcs. Here, we look from the mantle source perspective at the geological processes controlling the Li mobility in convergent margins, by characterizing a set of sub-arc mantle xenoliths from the southern Andes (Coyhaique, western Patagonia). The mineral trace element signatures and oxygen fugacity estimates (FMQ > + 3) in some of these peridotite xenoliths record the interaction with arc magmas enriched in fluid-mobile elements originally scavenged by slab dehydration. This subduction-related metasomatism was poorly effective on enhancing the Li inventory of the sub-arc lithospheric mantle, underpinning the inefficiency of slab-derived fluids on mobilizing Li through the mantle wedge. However, major and trace element compositions of mantle minerals in other xenoliths also record transient thermal and chemical anomalies associated with the percolation of slab window-related magmas, which exhibit an “adakite”-type geochemical fingerprint inherited by slab-derived melts produced during ridge subduction and slab window opening event. As these melts percolated through the shallow (7.2–16.8 kbar) and hot (952–1054 °C) lithospheric mantle wedge, they promoted the crystallization of metasomatic clinopyroxene having exceptionally high Li abundances (6–15 ppm). Numerical modeling shows that low degrees (< 10%) of partial melting of this Li-rich and fertile sub-arc lithospheric mantle generates primitive melts having two-fold Li enrichment (~13 ppm) compared with average subduction-zone basalts. Prolonged fractional crystallization of these melts produces extremely Li-enriched silicic rocks, which may stoke the Li inventory of mineralizing fluids in the shallow crust.

Lithium, rotation and metallicity in the open cluster M35

Context. Lithium (Li) abundance is an age indicator for G, K, and M stellar types, as its abundance decreases over time for these spectral types. However, despite all of the observational efforts made over the past few decades, the role of rotation, stellar activity, and metallicity in the depletion of Li is still unclear. Aims. Our purpose is to investigate how Li depletion is affected by rotation and metallicity in G and K members of the roughly Pleiades-aged open cluster M35. Methods. We have collected an initial sample of 165 candidate members observed with the WIYN/Hydra spectrograph. In addition, we have taken advantage of three previous spectroscopic studies of Li in M35. As a result, we have collected a final sample of 396 stars observed with the same instrument, which we have classified as non-members, possible non-members, possible members, and probable members of the cluster. We have measured iron abundances, Li equivalent widths, and Li abundances for the 110 M35 members added to the existing sample by this study. Finally, rotation periods for cluster members have been obtained from the literature or derived from Zwicky Transient Facility light curves. Results. We have confirmed that fast G and K rotators are Li-rich in comparison with slow rotators of similar effective temperature. This trend, which is also seen in previous studies, is more evident when binaries are not taken into account. Furthermore, while we derived an average metallicity of [Fe/H] = −0.26 ± 0.09 from our spectra, the distribution of Li in M35 is similar to those observed for the Pleiades and M34 open clusters, which have solar metallicity and slightly different ages. In addition, we have shown that an empirical relationship proposed to remove the contribution of the Fe I line at 670.75 nm to the blended feature at 670.78 nm overestimates by 5–15 mÅ the contribution of this iron line for M35 members. Conclusions. M35 fast G and K rotators have depleted less Li than their slower counterparts. Furthermore, a 0.2−0.3 dex difference in metallicity appears to make little difference in the Li distributions of open clusters with ages between 100 and 250 Myr.

Re-examining the Lithium abundance problem in Big-Bang nucleosynthesis

One of the three testaments in favor of the big bang theory is the prediction of the primordial elemental abundances in the big-bang nucleosynthesis (BBN). The Standard BBN is a parameter-free theory due to the precise knowledge of the baryon-to-photon ratio of the Universe obtained from studies of the anisotropies of cosmic microwave background radiation. Although the computed abundances of light elements during primordial nucleosynthesis and those determined from observations are in good agreement throughout a range of nine orders of magnitude, there is still a disparity of 7Li abundance overestimated by a factor of ∼2.5 when calculated theoretically. The number of light neutrino flavors, the neutron lifetime and the baryon-to-photon ratio in addition to the astrophysical nuclear reaction rates determine the primordial abundances. We previously looked into the impact of updating baryon-to-photon ratio and neutron lifetime and changing quite a few reaction rates on the yields of light element abundances in BBN. In this work, calculations are performed using new reaction rates for 3H(p, γ)4He, 6Li(p, γ)7Be, 7Be(p, γ)8B, 13N(p, γ)14O, 7Li(n, γ)8Li and 11B(n, γ)12B along with the latest measured value of neutron lifetime. We observe from theoretical calculations that these changes result in improvement by causing further reduction in the abundance of 7Li than calculated earlier.