- 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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- 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/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/III/68
- Title:
- List of Early-Type Chemically Peculiar Stars
- Short Name:
- III/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue is a subset of the "CATALOGUE OF STELLAR GROUPS" (CSG, Jaschek M. and Egret D., 1981BICDS..20...36J). It provides a list of identifications, positions, UBV photometry, subgroup and references for chemically peculiar stars corresponding to the following groups: Table 1: Helium abnormal stars Table 2: Ap stars Table 3: Am stars A bibliography file is also included.
- ID:
- ivo://CDS.VizieR/J/A+A/371/943
- Title:
- Lithium abundances for 185 main-sequence stars
- Short Name:
- J/A+A/371/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This table presents stellar atmospheric parameters, absolute magnitude, mass, age, equivalent width of the {lambda}6708 Li line, and non-LTE Li abundance. For the majority of stars the absolute magnitude has been derived from Hipparcos parallaxes but in a few cases (marked by :) a photometric value derived from the c_1_ index is given. Most stellar ages have errors of around 20% but those marked with `:' are more uncertain, and for stars close to the ZAMS no age is given.
- ID:
- ivo://CDS.VizieR/J/A+A/372/862
- Title:
- Lithium abundances in IC 2602 and IC 2391
- Short Name:
- J/A+A/372/862
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances and [Fe/H] for a sample of late-type stars in the young open clusters IC 2602 and IC 2391. Abundances are based on high resolution spectra obtained at ESO (3.6m + CASPEC) and CTIO (4m + echelle spectrograph)
- ID:
- ivo://CDS.VizieR/J/A+A/363/239
- Title:
- Lithium abundances in single giant stars
- Short Name:
- J/A+A/363/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the present work, we study the link between rotation and lithium abundance in giant stars of luminosity class III, on the basis of a large sample of 309 single stars of spectral type F, G and K. We have found a trend for a link between the discontinuity in rotation at the spectral type G0III and the behavior of lithium abundances around the same spectral type. The present work also shows that giant stars presenting the highest lithium contents, typically stars earlier than G0III, are those with the highest rotation rates, pointing for a dependence of lithium content on rotation, as observed for other luminosity classes. Giant stars later than G0III present, as a rule, the lowest rotation rates and lithium contents. A large spread of about five magnitudes in lithium abundance is observed for the slow rotators. Finally, single giant stars with masses 1.5<M/M_{sun}_<=2.5 w a clearest trend for a correlation between rotational velocity and lithium abundance.
- ID:
- ivo://CDS.VizieR/J/A+A/442/961
- Title:
- Lithium content of the Galactic Halo stars
- Short Name:
- J/A+A/442/961
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to the accurate determination of the baryon density of the universe by the recent cosmic microwave background experiments, updated predictions of the standard model of Big Bang nucleosynthesis now yield the initial abundance of the primordial light elements with unprecedented precision. In the case of ^7^Li, the CMB+SBBN value is significantly higher than the generally reported abundances for Pop II stars along the so-called Spite plateau. In view of the crucial importance of this disagreement, which has cosmological, galactic and stellar implications, we decided to tackle the most critical issues of the problem by revisiting a large sample of literature Li data in halo stars that we assembled following some strict selection criteria on the quality of the original analyses. We dissect our sample in search of new constraints on Li depletion in halo stars. By means of the Hipparcos parallaxes, we derive the evolutionary status of each of our sample stars, and re-discuss our derived Li abundances.
- ID:
- ivo://CDS.VizieR/J/AJ/162/229
- Title:
- 13 Magellanic Clouds metal-poor stars
- Short Name:
- J/AJ/162/229
- Date:
- 15 Mar 2022
- Publisher:
- CDS
- Description:
- The chemical abundances of a galaxy's metal-poor stellar population can be used to investigate the earliest stages of its formation and chemical evolution. The Magellanic Clouds are the most massive of the Milky Way's satellite galaxies and are thought to have evolved in isolation until their recent accretion by the Milky Way. Unlike the Milky Way's less massive satellites, little is known about the Magellanic Clouds' metal-poor stars. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey and archival data to target nine LMC and four SMC giants for high-resolution Magellan/MIKE spectroscopy. These nine LMC giants with -2.4<~[Fe/H]<~-1.5 and four SMC giants with -2.6<~[Fe/H]<~-2.0 are the most metal-poor stars in the Magellanic Clouds yet subject to a comprehensive abundance analysis. While we find that at constant metallicity these stars are similar to Milky Way stars in their {alpha}, light, and iron-peak elemental abundances, both the LMC and SMC are enhanced relative to the Milky Way in the r-process element europium. These abundance offsets are highly significant, equivalent to 3.9{sigma} for the LMC, 2.7{sigma} for the SMC, and 5.0{sigma} for the complete Magellanic Cloud sample. We propose that the r-process enhancement of the Magellanic Clouds' metal-poor stellar population is a result of the Magellanic Clouds' isolated chemical evolution and long history of accretion from the cosmic web combined with r-process nucleosynthesis on a timescale longer than the core-collapse supernova timescale but shorter than or comparable to the thermonuclear (i.e., Type Ia) supernova timescale.
- ID:
- ivo://CDS.VizieR/J/PAZh/31/437
- Title:
- Magnetic peculiar stars elemental abundances
- Short Name:
- J/PAZh/31/437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Temperature dependance of the abundances of the chemical elements Si, Ca, Cr and Fe in the atmospheres of normal, metallic-line (Am), magnetic peculiar (Ap) and pulsating magnetic peculiar (r0Ap) stars in the range 6000-15000K.
