- ID:
- ivo://CDS.VizieR/J/ApJ/882/40
- Title:
- Lanthanide fraction distribution of metal-poor stars
- Short Name:
- J/ApJ/882/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multimessenger observations of the neutron star merger GW170817 and its kilonova proved that neutron star mergers can synthesize large quantities of r-process elements. If neutron star mergers in fact dominate all r-process element production, then the distribution of kilonova ejecta compositions should match the distribution of r-process abundance patterns observed in stars. The lanthanide fraction (X_La_) is a measurable quantity in both kilonovae and metal-poor stars, but it has not previously been explicitly calculated for stars. Here we compute the lanthanide fraction distribution of metal-poor stars ([Fe/H]{<}-2.5) to enable comparison to current and future kilonovae. The full distribution peaks at log X_La_~-1.8, but r-process-enhanced stars ([Eu/Fe]>0.7) have distinctly higher lanthanide fractions: logX_La_>~-1.5. We review observations of GW170817 and find general consensus that the total logX_La_=-2.2+/-0.5, somewhat lower than the typical metal-poor star and inconsistent with the most highly r-enhanced stars. For neutron star mergers to remain viable as the dominant r-process site, future kilonova observations should be preferentially lanthanide-rich (including a population of ~10% with logX_La_>-1.5). These high-X_La_ kilonovae may be fainter and more rapidly evolving than GW170817, posing a challenge for discovery and follow-up observations. Both optical and (mid-)infrared observations will be required to robustly constrain kilonova lanthanide fractions. If such high-X_La_ kilonovae are not found in the next few years, that likely implies that the stars with the highest r-process enhancements have a different origin for their r-process elements.
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Search Results
- ID:
- ivo://CDS.VizieR/J/PASJ/57/109
- Title:
- Late-G giants abundances
- Short Name:
- J/PASJ/57/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Towards clarifying the properties of late-G giants, for which we are currently conducting a planet-search project at Okayama Astrophysical Observatory, an extensive spectroscopic study has been performed for our first target sample of fifty-seven G6-G9 III stars, in order to establish the atmospheric parameters (Teff, logg, vt, and [Fe/H]), the stellar mass along with the evolutionary status, and the photospheric abundances of various elements. It was confirmed that the conventional spectroscopic method of parameter determination using Fe I / II lines with the assumption of LTE works successfully for these evolved stars. We determined the abundances (relative to the Sun) of 19 elements, and examined how their [X/Fe] ratios behave themselves with the run of [Fe/H].
- ID:
- ivo://CDS.VizieR/J/A+A/631/A43
- Title:
- Late-type stars FeI & FeII NLTE line formation
- Short Name:
- J/A+A/631/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Iron plays a crucial role in studies of late-type stars. In their atmospheres, neutral iron is the minority species and lines of FeI are subject to the departures from local thermodynamic equilibrium (LTE). In contrast, one believes that LTE is a realistic approximation for FeII lines. The main source of the uncertainties in the non-LTE (NLTE) calculations for cool atmospheres is a treatment of inelastic collisions with hydrogen atoms. We investigate the effect of FeI+HI and FeII+HI collisions and their different treatment on the FeI/FeII ionisation equilibrium and iron abundance determinations for Galactic halo benchmark stars HD 84937, HD 122563, and HD 140283 and a sample of 38 very metal-poor (VMP) giants in the dwarf galaxies with well known distances. We perform the NLTE calculations for FeI-FeII with applying quantum-mechanical rate coefficients for collisions with HI from recent papers of Barklem (2018, Cat. J/A+A/612/A90B18), Yakovleva, Belyaev, and Kraemer (2018CP....515..369Y, YBK18), and Yakovleva, Belyaev, and Kraemer (2019MNRAS.483.5105Y , YBK19). We find that collisions with HI serve as efficient thermalisation processes for FeII, such that the NLTE abundance corrections for FeII lines do not exceed 0.02dex, in absolute value, for [Fe/H]~>-3 and reach +0.06dex at [Fe/H]~-4. For a given star, different treatments of FeI+HI collisions by B18 and YBK18 lead to similar average NLTE abundances from the FeI lines, although there exist discrepancies in the NLTE abundance corrections for individual lines. With using quantum-mechanical collisional data and the Gaia based surface gravity, we obtain consistent abundances from the two ionisation stages, FeI and FeII, for a red giant HD 122563. For a turn-off star HD 84937 and a subgiant HD 140283, we analyse the iron lines in the visible and the ultra-violet (UV, 1968 to 2990{AA}) range. For either FeI or FeII, abundances from the visible and UV lines are found to be consistent in each star. The NLTE abundances from the two ionisation stages agree within 0.10dex, when using the YBK18 data, and 0.13dex in case of B18. The FeI/FeII ionisation equilibrium is achieved for each star of our stellar sample in the dwarf galaxies, with the exception of stars at [Fe/H]~<-3.7.
- ID:
- ivo://CDS.VizieR/J/AJ/134/566
- Title:
- Leo II stellar kinematics
- Short Name:
- J/AJ/134/566
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the projected velocity dispersion profile for the remote (d=233kpc) Galactic dwarf spheroidal (dSph) galaxy Leo II, based on 171 discrete stellar radial velocities that were obtained from medium-resolution spectroscopy using the FLAMES/GIRAFFE spectrograph at the European Southern Observatory, Chile.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A84
- Title:
- Li abundance and mixing in giant stars
- Short Name:
- J/A+A/651/A84
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, idr6, and from the Gaia Early Data Release 3, EDR3. We selected a sample of main-sequence, sub-giant, and giant stars in which the Li abundance is measured by the Gaia-ESO survey. These stars belong to 57 open clusters with ages from 130Myr to about 7Gyr and to Milky Way fields, covering a range in [Fe/H] between -1.0 and +0.5dex, with few stars between -1.0 and -2.5dex. We studied the behaviour of the Li abundances as a function of stellar parameters. We inferred the masses of giant stars in clusters from the main-sequence turn-off masses, and for field stars through comparison with stellar evolution models using a maximum likelihood technique. We compared the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. The comparison with stellar evolution models confirms that classical models cannot reproduce the observed lithium abundances in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to~2 dex), making lithium the best element with which to constrain stellar mixing processes in low-mass stars. We discuss the nature of a sample of Li-rich stars. We demonstrate that the evolution of the surface abundance of Li in giant stars is a powerful tool for constraining theoretical stellar evolution models, allowing us to distinguish the effect of different mixing processes. For stars with well-determined masses, we find a better agreement of observed surface abundances and models with rotation-induced and thermohaline mixing. Rotation effects dominate during the main sequence and the first phases of the post-main-sequence evolution, and the thermohaline induced mixing after the bump in the luminosity function.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A92
- Title:
- Li abundance in solar analogues
- Short Name:
- J/A+A/562/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We want to study the effects of the formation of planets and planetary systems on the atmospheric Li abundance of planet host stars. In this work we present new determinations of lithium abundances for 326 main sequence stars with and without planets in the Teff range 5600-5900K. The 277 stars come from the HARPS sample, the remaining targets were observed with a variety of high-resolution spectrographs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/4038
- Title:
- Li abundance of giants in 3 globular clusters
- Short Name:
- J/MNRAS/449/4038
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of multiple populations in globular clusters has been well established thanks to high-resolution spectroscopy. It is widely accepted that distinct populations are a consequence of different stellar generations: intra-cluster pollution episodes are required to produce the peculiar chemistry observed in almost all clusters. Unfortunately, the progenitors responsible have left an ambiguous signature and their nature remains unresolved. To constrain the candidate polluters, we have measured lithium and aluminium abundances in more than 180 giants across three systems: NGC 1904, NGC 2808, and NGC 362. The present investigation along with our previous analysis of M12 and M5 affords us the largest database of simultaneous determinations of Li and Al abundances. Our results indicate that Li production has occurred in each of the three clusters. In NGC 362 we detected an M12-like behaviour, with first and second-generation stars sharing very similar Li abundances favouring a progenitor that is able to produce Li, such as AGB stars. Multiple progenitor types are possible in NGC 1904 and NGC 2808, as they possess both an intermediate population comparable in lithium to the first generation stars and also an extreme population, that is enriched in Al but depleted in Li. A simple dilution model fails in reproducing this complex pattern. Finally, the internal Li variation seems to suggest that the production efficiency of this element is a function of the cluster's mass and metallicity - low-mass or relatively metal-rich clusters are more adept at producing Li.
- ID:
- ivo://CDS.VizieR/J/A+A/409/251
- Title:
- Li abundances and velocities in F and G stars
- Short Name:
- J/A+A/409/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances have been determined in 127 F and G Pop I stars based on new measurements of the equivalent width of the {lambda}6707{AA} Li I line from their high resolution CCD spectra. Distances and absolute magnitudes of these stars have been obtained from the Hipparcos Catalogue (<I/239>) and their masses and ages derived, enabling us to investigate the behaviour of lithium as a function of these parameters. Based on their location on the HR diagram superposed on theoretical evolutionary tracks, the sample of the stars has been chosen to ensure that they have more or less completed their Li depletion on the main sequence.
- ID:
- ivo://CDS.VizieR/J/MNRAS/253/610
- Title:
- Li abundances for 81 F dwarfs
- Short Name:
- J/MNRAS/253/610
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances are presented for 81 main-sequence stars with effective temperatures of about 5800-6700K.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A69
- Title:
- Li abundances in F stars
- Short Name:
- J/A+A/576/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim, on the one hand, to study the possible differences of Li abundances between planet hosts and stars without detected planets at effective temperatures hotter than the Sun, and on the other hand, to explore the Li dip and the evolution of Li at high metallicities. We present lithium abundances for 353 main sequence stars with and without planets in the T_eff_ range 5900-7200K. We observed 265 stars of our sample with HARPS spectrograph during different planets search programs. We observed the remaining targets with a variety of high-resolution spectrographs. The abundances are derived by a standard local thermodynamic equilibrium analysis using spectral synthesis with the code MOOG and a grid of Kurucz ATLAS9 atmospheres. We find that hot jupiter host stars within the T_eff_ range 5900-6300K show lower Li abundances, by 0.14dex, than stars without detected planets. This offset has a significance at the level 7{sigma}, pointing to a stronger effect of planet formation on Li abundances when the planets are more massive and migrate close to the star. However, we also find that the average vsini of (a fraction of) stars with hot jupiters is higher on average than for single stars in the same T_eff_ region, suggesting that rotational-induced mixing (and not the presence of planets) might be the cause for a greater depletion of Li. We confirm that the mass-metallicity dependence of the Li dip is extended towards [Fe/H]~0.4dex (beginning at [Fe/H]~-0.4dex for our stars) and that probably reflects the mass-metallicity correlation of stars of the same T_eff_ on the main sequence. We find that for the youngest stars (<1.5Gyr) around the Li dip, the depletion of Li increases with vsini values, as proposed by rotationally-induced depletion models. This suggests that the Li dip consists of fast rotators at young ages whereas the most Li-depleted old stars show lower rotation rates (probably caused by the spin-down during their long lifes). We have also explored the Li evolution with [Fe/H] taking advantage of the metal-rich stars included in our sample. We find that Li abundance reaches its maximum around solar metallicity, but decreases in the most metal-rich stars, as predicted by some models of Li Galactic production.
