Lithium Abundances In Stars Research Articles

The evolution of lithium in FGK dwarf stars

This work aims to investigate the behaviour of the lithium abundance in stars with and without detected planets. Our study is based on a sample of 1332 FGK main-sequence stars with measured lithium abundances, for 257 of which planets were detected. Our method reviews the sample statistics and is addressed specifically to the influence of tides and orbital decay, with special attention to planets on close orbits, whose stellar rotational velocity is higher than the orbital period of the planet. In this case, tidal effects are much more pronounced. The analysis also covers the orbital decay on a short timescale, with planets spiralling into their parent star. Furthermore, the sample allows us to study the relation between the presence of planets and the physical properties of their host stars, such as the chromospheric activity, metallicity, and lithium abundance. In the case of a strong tidal influence, we cannot infer from any of the studies described that the behaviour of Li differs between stars that host planets and those that do not. Our sample includes stars with super-solar metallicity ([Fe/H] > 0.15 dex) and a low lithium abundance (A(Li) < 1.0 dex). This enabled us to analyse scenarios of the origin and existence of these stars. Considering the possible explanation of the F dip, we show that it is not a plausible scenario. Our analysis is based on a kinematic study and concludes that the possible time that elapsed in the travel from their birth places in the central regions of the Galaxy to their current positions in the solar neighbourhood is not enough to explain the high lithium depletion. It is remarkable that those of our high-metallicity low-lithium stars with the greatest eccentricity (e > 0.2) are closest to the Galactic centre. A dedicated study of a set of high-metallicity low-Li stars is needed to test the migration-depletion scenario.

Rotation and Lithium Confirmation of a 500 pc Halo for the Open Cluster NGC 2516*

Abstract Recent analyses of the Gaia data have identified diffuse stellar populations surrounding nearby open clusters. It is important to verify that these “halos,” “tails,” and “strings” are of similar ages and compositions as stars in the denser part of the cluster. We present an analysis of NGC 2516 (≈150 Myr), which has a classical tidal radius of 10 pc and an apparent halo of stars spanning 500 pc (20° on-sky). Combining photometry from Gaia, rotation periods from TESS, and lithium measurements from Gaia-ESO and GALAH, we find that the halo of NGC 2516 is the same age as the cluster’s core. Two-thirds of kinematically selected halo members out to 250 pc from the cluster center have rotation periods consistent with a gyrochronological age of 150 Myr. A comparison sample of field stars shows no such trend. The lithium abundances of stars in the halo are higher than in the field and correlated with the stellar rotation rate and binarity fraction, as has been noted in other young open clusters. Broadly speaking, this work supports a new paradigm wherein the halos of open clusters are often more populous than their cores. We highlight implications for spectroscopic survey targeting, open cluster dispersal, and planet searches around young stars.

Lithium abundance in a turnoff halo star on an extreme orbit

The lithium abundance in turnoff stars of the old population of our Galaxy is remarkably constant in the metallicity interval -2.8\textless{}[Fe/H] \textless{}-2.0, defining a plateau. The Li abundance of these turnoff stars is clearly lower than the abundance predicted by the primordial nucleosynthesis in the frame of the standard Big Bang nucleosynthesis. Different scenarios have been proposed for explaining this discrepancy, along with the very low scatter of the lithium abundance around the plateau. The recently identified very high velocity star, WISE J072543.88-235119.7 appears to belong to the old Galactic population, and appears to be an extreme halo star on a bound, retrograde Galactic orbit. In this paper, we study the abundance ratios and, in particular the lithium abundance, in this star. The available spectra (ESO-Very Large Telescope) are analyzed and the abundances of Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba are determined.The abundance ratios in WISE J072543.88-235119.7 are those typical of old turnoff stars. The lithium abundance in this star ~is in close agreement with the lithium abundance found in the metal-poor turnoff stars located at moderate distance from the Sun. This high velocity star confirms, in an extreme case, that the very small scatter of the lithium plateau persists independent of the dynamic and kinematic properties of the stars.

Chromospheric activity and lithium line variations in the spectra of the spotted star LQ Hydrae

Context. Although the relationship between lithium abundance in stars and their magnetic activity is commonly accepted, it is still unclear how the different phenomena related to it can increase the amount of Li, reduce its depletion, or be a source of bias for the measurements. Aims. We study the rotational modulation of chromospheric and photospheric parameters of the young, active, single K2 dwarf LQ Hya and their connection with the variability of the Li i 6708 A line. Methods. A total of 199 high-resolution STELLA spectra and quasi-simultaneous photometry were used to compute effective temperature, gravity, and chromospheric activity indicators such as Hα and Hβ emission, Balmer decrement, and chromospheric electron density, as a function of the rotational phase. The variation of the Li i 6708 A line was characterized in terms of equivalent width, abundance, and of 6 Li/ 7 Li isotopic ratio in the form of line shifts. Results. Photospheric and chromospheric parameters show clear rotational modulation. Effective temperatures and continuum variations reveal a higher concentration of cool spots on the side of the star on which we also detect stronger chromospheric activity. Increased electron densities and the modulation of the He i D3 line suggest that the source of this activity can be a combination of plages and repeated low-intensity flares. The Li line and other temperature-sensitive lines are clearly enhanced by the spots located on the most active side of the star. Li abundances calculated taking into account the temperature variations simultaneously show, although with high dispersion, a small overabundance of this element that correlates well with the surface magnetic activity. In addition, the Li line center is more intensely redshifted than in the other hemisphere, which might be interpreted as a weak enrichment of 6 Li.

Lithium abundance in the metal-poor open cluster NGC 2243

Lithium is a fundamental element for studying the mixing mechanisms acting in the stellar interiors, for understanding the chemical evolution of the Galaxy and the Big Bang nucleosynthesis. The study of Li in stars of open clusters (hereafter OC) allows a detailed comparison with stellar evolutionary models and permits us to trace its galactic evolution. The OC NGC 2243 is particularly interesting because of its low metallicity ([Fe/H]=$-0.54 \pm0.10$ dex). We measure the iron and lithium abundance in stars of the metal-poor OC NGC 2243. The first aim is to determine whether the Li dip extends to such low metallicities, the second is to compare the results of our Li analysis in this OC with those present in 47 Tuc, a globular cluster of similar metallicity. We performed a detailed analysis of high-resolution spectra obtained with the multi-object facility FLAMES at the ESO VLT 8.2m telescope. Lithium abundance was derived through line equivalent widths and the OSMARCS atmosphere models. We determine a Li dip center of 1.06 $M_\odot$, which is much smaller than that observed in solar metallicity and metal-rich clusters. This finding confirms and strengthens the conclusion that the mass of the stars in the Li dip strongly depends on stellar metallicity. The mean Li abundance of the cluster is $\log n{\rm (Li)}=2.70$ dex, which is substantially higher than that observed in 47 Tuc. We estimated an iron abundance of [Fe/H]=$-0.54 \pm0.10$ dex for NGC 2243, which is similar (within the errors) to previous findings. The [$ \alpha$/Fe] content ranges from $0.00\pm0.14$ for Ca to $0.20\pm0.22$ for Ti, which is low when compared to thick disk stars and to Pop II stars, but compatible with thin disk objects. We found a mean radial velocity of 61.9 $\pm$ 0.8 \kms for the cluster.

Mixing at young ages: beryllium abundances in cool main-sequence stars of the open clusters IC 2391 and IC 2602

The determination of lithium abundances in stars of young clusters have shown that they deplete Li by different degrees during their pre-main sequence phase. Beryllium abundances are complementary to the lithium ones, and can help tracing the mixing processes in the stellar interiors. Our aim is to derive beryllium abundances in a sample of G- and K-type stars of two young pre-main sequence open clusters, IC 2391 and IC 2602. The Be abundances are used to investigate the mixing of internal material in these stars. The reliability of the Be lines as abundance indicators in low-temperatures is also investigated in detail. We derived Be abundances from high-resolution, high signal-to-noise UVES/VLT spectra using spectrum synthesis and model atmospheres. Atmospheric parameters and other elemental abundances are adopted from a previous work. The sample stars have masses in the range between 0.80 < M/Msun < 1.20. They have been shown to differ in lithium abundance by about 0.60 dex, with lower A(Li) in cooler and lower mass stars. Here, we find that all the stars have the same Be abundance within the uncertainties. These observations show that the Be abundance is not affected by the mixing events in the pre-main sequence, in this mass range, in agreement with the expectation of evolutionary models. A comparison with Be abundances in older clusters shows that, contrary to the models, cool stars deplete Be during their main-sequence lifetime, confirming what has been previously suggested in the literature.

Lithium in stars with exoplanets

AbstractOur recent study of solar-type stars from the HARPS GTO sample provides highly accurate information with regard to Lithium abundances in stars with and without detected planets (Israelian et al. 2009). When the Li abundances of planet bearing stars are compared with the “single” stars, we find an excess of Li depletion in planet hosts with effective temperatures in the range 5700-5850 K. We also found that small amounts of Li have survived in the atmospheres of some planet-host solar analogs. Enhanced Li depletion in planet host stars puts constraints on mixing processes responsible for this phenomenon. We show that neither age nor metallicity are responsible for this observational fact.

Trojan Horse estimate of bare nucleus astrophysical S(E)-factor for the $\mathsf{^{6}}$Li(p,α)$^{\mathsf{3}}$He reaction and its astrophysical implications

The 6 Li(p, α) 3 He bare nucleus cross-section at astrophysical energies has been indirectly measured in the framework of the Trojan-Horse Method, finding an agreement within the experimental errors with the results of data extrapolations from direct methods. This result is thus an independent check of the extrapolation method used until now. The method of measure is recalled and the results are shown with particular attention to the bare cross section value at the Gamow energy. The quoted agreement between direct and indirect methods is discussed in the context of the surface lithium abundances in stars. It is shown that the problem of stellar lithium abundances is not at the nuclear physics level but it is an astrophysics problem that requires improvements in our knowledge of the mixing mechanisms, the reduction of the uncertainties on the other (non-nuclear) physical inputs, and more precise observational data.

Lithium abundances of the local thin disc stars

Lithium abundances are presented for a sample of 181 nearby F and G dwarfs with accurate Hipparcos parallaxes. The stars are on circular orbits about the Galactic centre and, hence, are identified as belonging to the thin disc. This sample is combined with two published surveys to provide a catalogue of lithium abundances, metallicities ([Fe/H]), masses, and ages for 451 F-G dwarfs, almost all belonging to the thin disc. The lithium abundances are compared and contrasted with published lithium abundances for F and G stars in local open clusters. The field stars span a larger range in [Fe/H] than the clusters for which [Fe/H] ≃ 0.0 ± 0.2. The initial (i.e. interstellar) lithium abundance of the solar neighbourhood, as derived from stars for which astration of lithium is believed to be unimportant, is traced from log ∈(Li) = 2.2 at [Fe/H] = -1 to log ∈(Li) = 3.2 at +0.1. This form for the evolution is dependent on the assumption that astration of lithium is negligible for the stars defining the relation. An argument is advanced that this latter assumption may not be entirely correct, and, the evolution of lithium with [Fe/H] may be flatter than previously supposed. A sharp Hyades-like Li dip is not seen among the field stars and appears to be replaced by a large spread among lithium abundances of stars more massive than the lower mass limit of the dip. Astration of lithium by stars of masses too low to participate in the Li dip is discussed. These stars show little to no spread in lithium abundance at a given [Fe/H] and mass.

Beryllium and Lithium Abundances in Stars with a Range of Metallicities

AbstractWe present new beryllium abundances for three unevolved stars with [Fe/H] in the range −0.4 to −1.6. The Be II doublet is detected in the three stars. A spectral synthesis analysis has been conducted to derive the abundances. We briefly discuss their Be and Li abundances, together with a wide sample of stars from the literature, in the context of mixing processes below the convection zone.

Lithium dilution through main-sequence mass loss

view Abstract Citations (88) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lithium Dilution through Main-Sequence Mass Loss Swenson, Fritz J. ; Faulkner, John Abstract We investigate the consequences of main-sequence mass loss for surface lithium abundances in stars through the use of evolving, mass-losing stellar models. In particular, we attempt to model lithium depletion observed in three areas: the sun, the Hyades G dwarfs, and the Hyades F dwarfs. Mass loss as an explanation for lithium depletion has mixed success. We conclude that mass loss can be marginal explanation for the solar lithium problem. In the case of the Hyades G dwarfs (the classical Hyades lithium problem) we find, contrary to preliminary investigations by ourselves and others, that mass loss cannot be a significant contributor to the depletion seen in these stars. Furthermore, we show that quasi-analytical means alone are sufficiently accurate to model the quantitative consequences of mass loss in these stars. For the Hyades F dwarfs, mass loss is a viable, although not particularly aesthetic, explanation. We highlight features that a theory of mass loss must posses to explain the remarkable pattern of lithium depletion seen among F dwarfs in the Hyades, in other clusters, and in the field. With the results of our calculations we limit the amount of mass that may have been lost on the main sequence by Hyades F and G dwarfs. Publication: The Astrophysical Journal Pub Date: August 1992 DOI: 10.1086/171686 Bibcode: 1992ApJ...395..654S Keywords: Lithium; Main Sequence Stars; Stellar Evolution; Stellar Mass Ejection; Stellar Models; Beryllium Isotopes; Dwarf Stars; Lithium Isotopes; Star Clusters; Astrophysics; ATOMIC DATA; STARS: ABUNDANCES; STARS: EVOLUTION; STARS: MASS LOSS; GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL full text sources ADS | data products SIMBAD (8)

Lithium Abundances of Stars in Open Clusters.

Lithium Abundances of Stars in Open Clusters.