- ID:
- ivo://CDS.VizieR/J/MNRAS/412/81
- Title:
- Lithium abundance in M4 red giants
- Short Name:
- J/MNRAS/412/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Li and Fe abundances for 87 stars in the globular cluster M4, obtained by using high-resolution spectra collected with GIRAFFE at the Very Large Telescope. The targets range from the turn-off up to the red giant branch bump. The Li abundance in the turn-off stars is uniform, with an average value equal to A(Li)=2.30+/-0.02dex (sigma=0.10dex), consistent with the upper envelope of Li content measured in other globular clusters and in the halo field stars, confirming also for M4 the discrepancy with the primordial Li abundance predicted by Wilkinson Microwave Anisotropy Probe+ big bang nucleosynthesis (WMAP+BBNS).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/716/L166
- Title:
- Lithium abundances in red giants of M4
- Short Name:
- J/ApJ/716/L166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of Li and proton-capture element abundances in globular cluster (GC) giants allows us to constrain several key questions on the multiple population scenarios in GCs, from formation and early evolution to pollution and dilution mechanisms. In this Letter, we present our results on Li abundances for a large sample of giants in the intermediate-metallicity GC NGC 6121 (M4), for which Na and O have been already determined by Marino et al. (2008, Cat. J/A+A/490/625). The stars analyzed are both below and above the red giant branch bump luminosity. We found that the first and second generation stars share the same Li content, suggesting that a Li production must have occurred. This provides strong observational evidence supporting the scenario in which asymptotic giant branch stars are GC polluters.
- ID:
- ivo://CDS.VizieR/J/ApJ/713/L1
- Title:
- Lithium and proton-capture elements in 47 Tuc
- Short Name:
- J/ApJ/713/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous surveys in a few metal-poor globular clusters (GCs) showed that the determination of abundances for Li and proton-capture elements offers a key tool to address the intracluster pollution scenario. In this Letter, we present Na, O, and Li abundances in a large sample of dwarf stars in the metal-rich GC 47 Tucanae. We found a clear Na-O anticorrelation, in good agreement with what obtained for giant members by Carretta et al. (2009, Cat. J/A+A/505/117). While lithium and oxygen abundances appear to be positively correlated with each other, there is a large scatter, well exceeding observational errors, and no anticorrelation with sodium. These findings suggest that Li depletion, due to mechanisms internal to the stars (which are cooler and more metal-rich than those on the Spite plateau), combines with the usual pollution scenario responsible for the Na-O anticorrelation.
- ID:
- ivo://CDS.VizieR/J/A+A/519/L3
- Title:
- Lithium content of {omega} Cen
- Short Name:
- J/A+A/519/L3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A discrepancy has emerged between the cosmic lithium abundance inferred by the WMAP satellite measurement coupled with the prediction of the standard big-bang nucleosynthesis theory, and the constant Li abundance measured in metal-poor halo dwarf stars (the so-called Spite plateau). Several models are being proposed to explain this discrepancy, involving either new physics, in situ depletion, or the efficient depletion of Li in the pristine Galaxy by a generation of massive first stars. The realm of possibilities may be narrowed considerably by observing stellar populations in different galaxies, which have experienced different evolutionary histories. The omega Centauri stellar system is commonly considered as the remnant of a dwarf galaxy accreted by the Milky Way. We investigate the lithium content of a conspicuous sample of unevolved stars in this object.
- ID:
- ivo://CDS.VizieR/J/A+A/505/L13
- Title:
- Lithium in globular NGC 6397
- Short Name:
- J/A+A/505/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most globular clusters are believed to host a single stellar population. They can thus be considered a good place to study the Spite plateau and to search for possible evolutionary modifications of the Li content. We want to determine the Li content of subgiant (SG) and main sequence (MS) stars of the old, metal-poor globular cluster NGC 6397. This work was aimed not only at studying possible Li abundance variations but also to investigate the cosmological Li discrepancy.
- ID:
- ivo://CDS.VizieR/J/A+A/653/A13
- Title:
- Lithium in NGC 2243 and NGC 104
- Short Name:
- J/A+A/653/A13
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to determine the initial Li content of two clusters of similar metallicity but very different age, the old open cluster NGC 2243 and the metal-rich globular cluster NGC 104. We compare the lithium abundances derived for a large sample of stars (from the turn-off to the red giant branch) in each cluster. For NGC 2243, the Li abundances are taken from the catalogues released by the Gaia-ESO Public Spectroscopic Survey, while for NGC 104 we measured the Li abundance using FLAMES/GIRAFFE spectra, which include both archival data and new observations.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A33
- Title:
- Lithium in the LRGB of 5 globular clusters
- Short Name:
- J/A+A/657/A33
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Lithium is one of the few elements produced during the Big Bang Nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of different astrophysical problems. Stars in the lower red giant branch allow studying globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/135
- Title:
- Lithium-rich giants in globular clusters
- Short Name:
- J/ApJ/819/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2+/-0.1)% for the RGB, (1.6+/-1.1)% for the AGB, and (0.3+/-0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.
- ID:
- ivo://CDS.VizieR/J/AJ/153/154
- Title:
- LMC NIR survey. IV. Type II Cepheid variables
- Short Name:
- J/AJ/153/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHK_s_) wavelengths. Our sample consists of 81 variables with accurate periods and optical (VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and K_s_-band data in the Galactic bulge from VISTA Variables in Via Lactea survey (2010NewA...15..433M) and use them to obtain robust mean magnitudes. We derive period-luminosity (P-L) relations in the near-infrared and Period-Wesenheit (P-W) relations by combining optical and near-infrared data. Our P-L and P-W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P-L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 (Cat. I/337) for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic K_s_-band P-L relation, resulting in a distance modulus to the LMC of {mu}_LMC_=18.54+/-0.08 mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within 2{sigma}) with estimates based on the M_V_-[Fe/H] relation for horizontal branch stars.
- ID:
- ivo://CDS.VizieR/J/AJ/142/48
- Title:
- LMC star clusters structural parameters
- Short Name:
- J/AJ/142/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze the radial luminosity profiles of a sample of 1066 stellar clusters in the Large Magellanic Cloud (LMC). By design, this study closely follows the compilation by Hill & Zaritsky (2006, Cat. J/AJ/131/414 of the structural parameters of stellar clusters in the Small Magellanic Cloud (SMC). Both King and Elson-Fall-Freeman model profiles are fit to V-band surface brightness profiles measured from the Magellanic Cloud Photometric Survey images. We tabulate the concentration, central surface brightness, tidal radii, 90% enclosed luminosity radii (r_90_), and local background luminosity density. Over two-thirds of the clusters in the sample are adequately fit by one or both of these models. One notable and systematic exception, as in the SMC, is those clusters that lack a central brightness concentration, the "ring" clusters. While the bulk properties of the clusters are similar between the LMC and SMC populations, we find that the LMC lacks clusters that are as large, either in terms of core radii or r90, as the largest in the SMC, perhaps a signature of larger tidal stresses in the LMC.
