- ID:
- ivo://CDS.VizieR/J/A+AS/102/361
- Title:
- Li abundances in galactic C-stars
- Short Name:
- J/A+AS/102/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The equivalent widths and abundances of Lithium in galactic carbon stars are presented in Table 1. The observations were made during 1990 and 1991 in 3 different observatories: Roque de los Muchachos and Calar Alto (Spain), and La Silla (Chile). The resolving power of the spectra is 15000-2000 for the spanish observations, and about 60000 for the stars observed at La Silla.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/468/663
- Title:
- Li abundances in solar-analog stars
- Short Name:
- J/A+A/468/663
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is known that the surface lithium abundances of field solar-analog G dwarfs show a large dispersion of >~2dex (among which our Sun is located at the lower end) despite the similarity of stellar parameters, and planet-host stars tend to show comparatively lower Li abundances in the narrow Teff range. To investigate the reason for these phenomena, an extensive study of Li abundances and their dependence on stellar parameters was carried out for a homogeneous sample of 118 selected solar analogs based on high-dispersion spectra obtained at Okayama Astrophysical Observatory.
- ID:
- ivo://CDS.VizieR/J/A+A/515/A93
- Title:
- Li abundances in solar-analog stars. II.
- Short Name:
- J/A+A/515/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We previously attempted to ascertain why the LiI 6708 line-strengths of Sun-like stars differ so significantly despite the superficial similarities of stellar parameters. We carried out a comprehensive analysis of 118 solar analogs and reported that a close connection exists between the Li abundance (A_Li_) and the line-broadening width (v_r+m_) mainly contributed by rotational effect), which led us to conclude that stellar rotation may be the primary control of the surface Li content. To examine our claim in more detail, we study whether the degree of stellar activity exhibits a similar correlation with the Li abundance, which is expected because of the widely believed close connection between rotation and activity.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A106
- Title:
- Li abundances in the FGK dwarfs
- Short Name:
- J/A+A/547/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of the present study is to determine the Li abundances for a large set of the FGK dwarfs and to analyse the connections between the Li content, stellar parameters, and activity. The atmospheric parameters, rotational velocities and the Li abundances were determined from a homogeneous collection of the echelle spectra with high resolution and a high signal-to-noise ratio. The rotational velocities vsini were determined by calibrating the cross-correlation function. The effective temperatures Teff were estimated by the line depth ratio method. The surface gravities logg were computed by two methods: the iron ionization balance and the parallax. The LTE Li abundances were computed using synthetic spectra method. The behaviour of the Li abundance was examined in correlation with Teff, [Fe/H], as well as with vsini and the level of activity in three stellar groups of the different temperature range. The stellar parameters and the Li abundances are presented for 150 slow rotating stars of the lower part of MS. The studied stars show a decline in the Li abundance with decreasing temperature Teff and a significant spread, which should be due to the difference of age of stars. The correlations between the Li abundances, rotational velocities vsini, and the level of the chromospheric activity were discovered for the stars with 6000>Teff>5700K, and it is tighter for the stars with 5700>Teff>5200K. The target stars with Teff<5200K do not show any correlation between log A(Li) and vsini. The relationship between the chromospheric and coronal fluxes in active with detected Li as well as in less active stars gives a hint that there exist different conditions in the action of the dynamo mechanism in those stars. We found that the Li-activity correlation is evident only in a restricted temperature range and the Li abundance spread seems to be present in a group of low chromospheric activity stars that also show a broad spread in the chromospheric vs. coronal activity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1368
- Title:
- Li abundances & vsini for star-planet systems
- Short Name:
- J/MNRAS/403/1368
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine Li abundances and vsini values from new spectra of 53 stars with Doppler-detected planets not included in our previous papers in this series. We also examine two sets of stars without detected planets, which together serve as our comparison sample. Using the method of comparison of Li abundances and vsini values between two sets of stars we introduced in Gonzalez, we confirm that these two quantities are smaller among stars with planets (SWPs) compared to stars without detected planets near the solar temperature. The transition from low to high Li abundance among SWPs occurs near 5850K, a revision of about 50K from our previous determination. The transition from low to high vsini occurs near 6000K, but this temperature is not as well constrained.
- ID:
- ivo://CDS.VizieR/J/AJ/158/163
- Title:
- Li abundance values for stars in NGC 6819
- Short Name:
- J/AJ/158/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopy of 333 NGC 6819 stars and Gaia astrometry are used to map Li evolution from the giant branch tip to 0.5 mag below the Li dip. Isochrone comparison with [Fe/H]=-0.04, based upon neural network spectroscopic analysis, produces an age of 2.25 (2.4) Gyr for E(B-V)=0.16 (0.14) and (m-M)=12.40 (12.29). Despite originating outside the Li dip, only 10% of single subgiants/giants have measurable Li. Above the Li dip, the limiting A(Li) for single stars is 3.2+/-0.1 but the lower range is comparable to that found within the dip. The F-dwarf Li dip profile agrees with the Hyades/Praesepe, evolved forward. The Li level among stars populating the plateau fainter than the Li dip is A(Li)=2.83+/-0.16; the dispersion is larger than expected from spectroscopic error alone. Comparison of Li and V_ROT_ distributions among turnoff stars in NGC 7789, NGC 2506, NGC 3680, and NGC 6819 indicates that rotational spindown from the main sequence is critical in defining the boundaries of the Li dip. For higher-mass dwarfs, spindown is likewise correlated with Li depletion, creating a second dip, but at higher mass and on a longer timescale. The Li distribution among evolved stars of NGC 6819 is more representative of the older M67, where subgiant and giant stars emerge from within the Li dip, than the younger NGC 7789, where a broad range in V_ROT_ among the turnoff stars likely produces a range in mass among the giants.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A157
- Title:
- Li and Na in globular cluster M4
- Short Name:
- J/A+A/539/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundance inhomogeneities of light elements observed in globular clusters (GCs), and notably the ubiquitous Na-O anti-correlation, are generally interpreted as evidence that GCs comprise several generations of stars. There is an on-going debate as to the nature of the stars, which produce the inhomogeneous elements, and investigating the behavior of several elements is a way to shed new light on this problem. We aim at investigating the Li and Na content of the GC M4, that is known to have a well defined Na-O anti-correlation. We obtained moderate resolution (R=17000-18700) spectra for 91 main sequence (MS)/sub-giant branch stars of M4 with the Giraffe spectrograph at the FLAMES/VLT ESO facility. Using model atmospheres analysis we measured lithium and sodium abundances.
- ID:
- ivo://CDS.VizieR/J/AJ/159/90
- Title:
- Li, C and O abundances of FGK stars
- Short Name:
- J/AJ/159/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abundances of lithium, carbon, and oxygen have been derived using spectral synthesis for a sample of 249 bright F, G, and K Northern Hemisphere dwarf stars from the high-resolution spectra acquired with the Vilnius University Echelle Spectrograph (VUES) at the Moletai Astronomical Observatory of Vilnius University. The sample stars have metallicities, effective temperatures, and ages between -0.7-0.4dex, 5000-6900K, 1-12Gyr, accordingly. We confirm a so far unexplained lithium abundance decrease at supersolar metallicities --A(Li) in our sample stars, which drop by 0.7dex in the [Fe/H] range from +0.10 to +0.55dex. Furthermore, we identified stars with similar ages, atmospheric parameters, and rotational velocities, but with significantly different lithium abundances, which suggests that additional specific evolutionary factors should be taken into account while interpreting the stellar lithium content. Nine stars with predominantly supersolar metallicities, i.e., about 12% among 78 stars with C and O abundances determined, have the C/O number ratios larger than 0.65, thus may form carbon-rich rocky planets. Ten planet-hosting stars, available in our sample, do not show a discernible difference from the stars with no planets detected regarding their lithium content.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/220
- Title:
- Lick indices for FGK stars
- Short Name:
- J/MNRAS/442/220
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present FEROS-Lick/SDSS, an empirical data base of Lick/SDSS spectral indices of FGK stars to be used in population synthesis projects for discriminating different stellar populations within the integrated light of galaxies and globular clusters. From about 2500 FEROS stellar spectra obtained from the European Southern Observatory Science Archive Facility, we computed line-strength indices for 1085 non-supergiant stars with atmospheric parameter estimates from the AMBRE project. Two samples of 312 dwarfs and of 83 subgiants} with solar chemical composition and no significant {alpha}-element abundance enhancement are used to compare their observational indices with the predictions of the Lick/SDSS library of synthetic indices. In general, the synthetic library reproduces very well the behaviour of observational indices as a function of temperature, but in the case of low-temperature (T_eff_<~5000K) dwarfs; low-temperature subgiants are not numerous enough to derive any conclusion. Several possible causes of the disagreement are discussed and promising theoretical improvements are presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/637/1102
- Title:
- Lick indices for metal-rich stars
- Short Name:
- J/ApJ/637/1102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present empirical calibrations that provide estimates of stellar metallicity, effective temperature, and surface gravity as a function of Lick IDS indices. These calibrations have been derived from a training set of 261 stars for which (1) high-precision measurements of [Fe/H], Teff, and log(g) have been made using spectral-synthesis analysis of HIRES spectra, and (2) Lick indices have also been measured.
