- 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.
Number of results to display per page
Search Results
- 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/ApJ/724/154
- Title:
- Lithium abundances in stars with planets
- Short Name:
- J/ApJ/724/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents a homogeneous determination of lithium abundances in a large sample of giant-planet-hosting stars (N=117) and a control sample of disk stars without detected planets (N=145). The lithium abundances were derived using a detailed profile fitting of the LiI doublet at 6708{AA} in LTE. The planet-hosting and comparison stars were chosen to have significant overlap in their respective physical properties, including effective temperatures, luminosities, masses, metallicities, and ages. The combination of uniform data and homogeneous analysis with well-selected samples makes this study well suited to probe for possible differences in the lithium abundances found in planet-hosting stars. An overall comparison between the two samples reveals no obvious differences between stars with and without planets. A closer examination of the behavior of the Li abundances over a narrow range of effective temperature (5700K<=T_eff_<=5850K) indicates subtle differences between the two stellar samples; this temperature range is particularly sensitive to various physical processes that can deplete lithium.
- ID:
- ivo://CDS.VizieR/J/ApJ/785/94
- Title:
- Lithium abundances of a large sample of red giants
- Short Name:
- J/ApJ/785/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The lithium abundances for 378 G/K giants are derived with non-local thermodynamic equilibrium correction considered. Among these are 23 stars that host planetary systems. The lithium abundance is investigated, as a function of metallicity, effective temperature, and rotational velocity, as well as the impact of a giant planet on G/K giants. The results show that the lithium abundance is a function of metallicity and effective temperature. The lithium abundance has no correlation with rotational velocity at v sin i<10 km/s. Giants with planets present lower lithium abundance and slow rotational velocity (v sin i<4 km/s). Our sample includes three Li-rich G/K giants, 36 Li-normal stars, and 339 Li-depleted stars. The fraction of Li-rich stars in this sample agrees with the general rate of less than 1% in the literature, and the stars that show normal amounts of Li are supposed to possess the same abundance at the current interstellar medium. For the Li-depleted giants, Li-deficiency may have already taken place at the main sequence stage for many intermediate mass (1.5-5 M_{sun}_)G/K giants. Finally, we present the lithium abundance and kinematic parameters for an enlarged sample of 565 giants using a compilation of the literature, and confirm that the lithium abundance is a function of metallicity and effective temperature. With the enlarged sample, we investigate the differences between the lithium abundance in thin-/thick-disk giants, which indicate that the lithium abundance in thick-disk giants is more depleted than that in thin-disk giants.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A36
- Title:
- Lithium abundances of bulge RGB stars
- Short Name:
- J/A+A/538/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A small number of K-type giants on the red giant branch (RGB) is known to be very rich in lithium (Li). This fact is not accounted for by standard stellar evolution theory. The exact phase and mechanism of Li enrichment is still a matter of debate. Our goal is to probe the abundance of Li along the RGB, from its base to the tip, to confine Li-rich phases that are supposed to occur on the RGB. For this end, we obtained medium-resolution spectra with the FLAMES spectrograph at the VLT in GIRAFFE mode for a large sample of 401 low-mass RGB stars located in the Galactic bulge. The Li abundance was measured in the stars with a detectable Li 670.8 nm line by means of spectral synthesis with COMARCS model atmospheres. A new 2MASS J-K-Teff calibration from COMARCS models is presented in the Appendix. Thirty-one stars with a detectable Li line were identified, three of which are Li-rich according to the usual criterion (log{epsilon}_Li_>1.5). The stars are distributed all along the RGB, not concentrated in any particular phase of the red giant evolution (e.g. the luminosity bump or the red clump). The three Li-rich stars are clearly brighter than the luminosity bump and red clump, and do not show any signs of enhanced mass loss. We conclude that the Li enrichment mechanism cannot be restricted to a clearly defined phase of the RGB evolution of low-mass stars (M~1M_{sun}_), contrary to earlier suggestions from disk field stars.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/45
- Title:
- Lithium abundances of F-K stars
- Short Name:
- J/PASJ/57/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An extensive profile-fitting analysis was performed for the Li(+Fe) 6707-6708{AA} feature of nearby 160 F-K dwarfs/subgiants (including 27 planet-host stars) in the Galactic disk (7000K>~Teff>~5000K, -1<~[Fe/H]<~+0.4), in order to establish the photospheric lithium abundances of these stars. The non-LTE effect (though quantitatively insignificant) was taken into account based on our statistical equilibrium calculations, which were carried out on an adequate grid of models. Our results confirmed most of the interesting observational characteristics revealed by recently published studies, such as the bimodal distribution of the Li abundances for stars at Teff>~6000K, the satisfactory agreement of the upper envelope of the A(Li) vs. [Fe/H] distribution with the theoretical models, the existence of a positive correlation between A(Li) and the stellar mass, and the tendency of lower lithium abundances of planet-host stars (as compared to stars without planets) at the narrow ``transition'' region of 5900K>~Teff>~5800K. The solar Li abundance derived from this analysis is 0.92 (H=12.00), which is by 0.24dex lower than the widely referenced standard value of 1.16.
- ID:
- ivo://CDS.VizieR/J/A+A/493/601
- Title:
- Lithium abundances of halo dwarfs
- Short Name:
- J/A+A/493/601
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of the Spite plateau in the abundances of ^7^Li^ for metal-poor stars led to the determination of an observationally deduced primordial lithium abundance. However, after the success of the Wilkinson Microwave Anisotropy Probe (WMAP) in determining the baryon density, {Omega}_B_h^2^, there was a discrepancy between observationally determined and theoretically determined abundances in the case of ^7^Li. One of the most important uncertain factors in the calculation of the stellar ^7^Li abundance is the effective temperature, Teff. We use sixteen metal-poor halo dwarfs to calculate new Teff values using the excitation energy method. With this temperature scale we then calculate new Li abundances for this group of stars in an attempt to resolve the ^7^Li discrepancy.
- ID:
- ivo://CDS.VizieR/J/ApJ/855/115
- Title:
- Lithium abundances of KOIs from CKS spectra
- Short Name:
- J/ApJ/855/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The lithium doublet at 6708{AA} provides an age diagnostic for main sequence FGK dwarfs. We measured the abundance of lithium in 1305 stars with detected transiting planets from the Kepler mission using high-resolution spectroscopy. Our catalog of lithium measurements from this sample has a range of abundance from A(Li)=3.11+/-0.07 to an upper limit of -0.84dex. For a magnitude-limited sample that comprises 960 of the 1305 stars, our Keck-HIRES spectra have a median signal-to-noise ratio of 45 per pixel at ~6700{AA} with spectral resolution {lambda}/{Delta}{lambda}=R=55000. We identify 80 young stars that have A(Li) values greater than the Hyades at their respective effective temperatures; these stars are younger than ~650Myr, the approximate age of the Hyades. We then compare the distribution of A(Li) with planet size, multiplicity, orbital period, and insolation flux. We find larger planets preferentially in younger systems, with an A-D two-sided test p-value=0.002, a>3{sigma} confidence that the older and younger planet samples do not come from the same parent distribution. This is consistent with planet inflation/photoevaporation at early ages. The other planet parameters (Kepler planet multiplicity, orbital period, and insolation flux) are uncorrelated with age.
- 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/613/A63
- Title:
- Lithium content for 148 Pleiades stars
- Short Name:
- J/A+A/613/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of lithium abundance over a star's lifetime is indicative of transport processes operating in the stellar interior. Aims. We revisit the relationship between lithium content and rotation rate previously reported for cool dwarfs in the Pleiades cluster. Methods. We derive new LiI 670.8nm equivalent width measurements from high-resolution spectra obtained for low-mass Pleiades members. We combine these new measurements with previously published ones, and use the Kepler/K2 rotational periods recently derived for Pleiades cool dwarfs to investigate the lithium-rotation connection in this 125Myr-old cluster. Results. The new data confirm the correlation between lithium equivalent width and stellar spin rate for a sample of 51 early K-type members of the cluster, where fast rotating stars are systematically lithium-rich compared to slowly rotating ones. The correlation is valid for all stars over the (J-Ks) color range 0.50-0.70mag, corresponding to a mass range from about 0.75 to 0.90M_{sun}_, and may extend down to lower masses. Conclusions. We argue that the dispersion in lithium equivalent widths observed for cool dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium abundances, and suggest that the physical origin of the lithium dispersion pattern is to be found in the pre-main sequence rotational history of solar-type stars.