- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/610/A38
- Title:
- Li enrichment histories of the thick/thin disc
- Short Name:
- J/A+A/610/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundance in most of the warm metal-poor main sequence stars shows a constant plateau (A(Li)~2.2dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium at the solar system formation time, show a lithium abundance A(Li)~3.26dex. This pattern reflects the Li enrichment history of the interstellar medium during the Galaxy lifetime. After the initial Li production in Big Bang Nucleosynthesis, the sources of the enrichment include AGB stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalog and find a Li-[alpha/Fe] anticorrelation independent of [Fe/H], Teff, and log(g). Since in stellar evolution different {alpha} enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/ApJ/795/23
- Title:
- Line list for stellar chemical abundances
- Short Name:
- J/ApJ/795/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The achievable level of precision on photospheric abundances of stars is a major limiting factor on investigations of exoplanet host star characteristics, the chemical histories of star clusters, and the evolution of the Milky Way and other galaxies. While model-induced errors can be minimized through the differential analysis of spectrally similar stars, the maximum achievable precision of this technique has been debated. As a test, we derive differential abundances of 19 elements from high-quality asteroid-reflected solar spectra taken using a variety of instruments and conditions. We treat the solar spectra as being from unknown stars and use the resulting differential abundances, which are expected to be zero, as a diagnostic of the error in our measurements. Our results indicate that the relative resolution of the target and reference spectra is a major consideration, with use of different instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of the same instrument at different epochs for the two spectra has a much smaller effect (~0.007 dex). The asteroid used to obtain the solar standard also has a negligible effect (~0.006 dex). Assuming that systematic errors from the stellar model atmospheres have been minimized, as in the case of solar twins, we confirm that differential chemical abundances can be obtained at sub-0.01 dex precision with due care in the observations, data reduction, and abundance analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/146
- Title:
- Line-of-sight velocities from bar simulations
- Short Name:
- J/ApJ/812/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extract the resonant orbits from an N-body bar that is a good representation of the Milky Way, using the method recently introduced by Molloy et al. (2015ApJ...804...80M). By decomposing the bar into its constituent orbit families, we show that they are intimately connected to the boxy-peanut shape of the density. We highlight the imprint due solely to resonant orbits on the kinematic landscape toward the Galactic center. The resonant orbits are shown to have distinct kinematic features and may be used to explain the cold velocity peak seen in the Apache Point Observatory Galactic Evolution Experiment commissioning data. We show that high velocity peaks are a natural consequence of the motions of stars in the 2:1 orbit family and that stars on other higher order resonances can contribute to the peaks. The locations of the peaks vary with bar angle and, with the tacit assumption that the observed peaks are due to the 2:1 family, we find that the locations of the high velocity peaks correspond to bar angles in the range 10{deg}<~{theta}_bar_<~25{deg}. However, some important questions about the nature of the peaks remain, such as their apparent absence in other surveys of the Bulge and the deviations from symmetry between equivalent fields in the north and south. We show that the absence of a peak in surveys at higher latitudes is likely due to the combination of a less prominent peak and a lower number density of bar supporting orbits at these latitudes.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A18
- Title:
- Lithium abundances in AMBRE stars
- Short Name:
- J/A+A/595/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of this paper is to investigate the lithium stellar content of Milky Way stars in order to put constraints on the lithium chemical enrichment in our Galaxy, in particular in both the thin and thick discs. We show that the interstellar lithium abundance increases with metallicity by 1dex from [M/H]=-1dex to +0.0dex. Moreover, we find that this lithium ISM abundance decreases by about 0.5dex at super-solar metallicity. Based on a chemical separation, we also observed that the stellar lithium content in the thick disc increases rather slightly with metallicity while the thin disc shows a steeper increase. The lithium abundance distribution of alpha-rich metal-rich stars has a peak at A(Li)~3 dex. We conclude that the thick disc stars suffered of a low lithium chemical enrichment, showing lithium abundances rather close to the Spite plateau while the thin disc stars clearly show an increasing lithium chemical enrichment with the metallicity, probably thanks to the contribution of low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A151
- Title:
- Lithium abundances in 714 F and G dwarf stars
- Short Name:
- J/A+A/615/A151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a detailed analysis of Li in 714 nearby dwarf stars. Li abundances were determined through spectral line synthesis of the Li feature at 670.8 nm. The stellar sample traces the evolution of the Galactic thin and thick disks in the solar neighbourhood, and is the same as previously analysed by Bensby et al. (2014, Cat. J/A+A/562/A71) where stellar parameters and ages were taken from. The same sample was also used in Battistini & Bensby (2015, Cat. J/A+A/577/A9, 2016, Cat. J/A+A/586/A49) wherein abundances for odd iron-peak elements and r- and s-process elements can be found.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A130
- Title:
- Lithium abundances in microlensed bulge dwarfs
- Short Name:
- J/A+A/634/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances are presented for 91 dwarf and subgiant stars in the Galactic bulge. The analysis is based on line synthesis of the ^7^Li line at 6707{AA} in high-resolution spectra obtained during gravitational microlensing events, when the brightnesses of the targets were highly magnified. Our main finding is that bulge stars at sub-solar metallicities that are older than about eight billion years do not show any sign of Li production; that is, the Li trend with metallicity is flat or even slightly declining. This indicates that no lithium was produced during the first few billion years in the history of the bulge. This finding is essentially identical to what is seen for the (old) thick disk stars in the solar neighbourhood, and adds another piece of evidence for a tight connection between the metal-poor bulge and the Galactic thick disk. For the bulge stars younger than about eight billion years, the sample contains a group of stars at very high metallicities at [Fe/H]~=+0.4 that have lithium abundances in the range A(Li)=2.6-2.8. In the solar neighbourhood the lithium abundances have been found to peak at A(Li)~=3.3 at [Fe/H]~=+0.1 and then decrease by 0.4-0.5dex when reaching [Fe/H]~=+0.4. The few bulge stars that we have at these metallicities seem to support this declining A(Li) trend. This could indeed support the recent claim that the low A(Li) abundances at the highest metallicities seen in the solar neighbourhood could be due to stars from the inner disk, or the bulge region, that have migrated to the solar neighbourhood.
- 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/151/88
- Title:
- LMC NIR Synoptic Survey. II. Wesenheit relations
- Short Name:
- J/AJ/151/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new near-infrared (NIR) Cepheid period-Wesenheit (P-W) relations in the LMC using time-series observations from the Large Magellanic Cloud NIR Synoptic Survey. We also derive optical+NIR P-W relations using V and I magnitudes from the Optical Gravitational Lensing Experiment. We employ our new JHK_s_ data to determine an independent distance to the LMC of {mu}_LMC_=18.47+/-0.07 (statistical) mag, using an absolute calibration of the Galactic relations based on several distance determination methods and accounting for the intrinsic scatter of each technique. We also derive new NIR period-luminosity and Wesenheit relations for Cepheids in M31 using observations from the Panchromatic Hubble Andromeda Treasury survey. We use the absolute calibrations of the Galactic and LMC W_J,H_ relations to determine the distance modulus of M31, {mu}_M31_=24.46+/-0.20 mag. We apply a simultaneous fit to Cepheids in several Local Group galaxies covering a range of metallicities (7.7<12+log[O/H]<8.6 dex) to determine a global slope of -3.244+/-0.016 mag/dex for the W_J,H_ relation and obtain robust distance estimates. Our distances are in good agreement with recent TRGB based distance estimates and we do not find any evidence for a metallicity dependence in the NIR P-W relations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/483/299
- Title:
- Local Bubble & Gould Belt polarization
- Short Name:
- J/MNRAS/483/299
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We create and analyse the largest up-to-date all-sky compilation of the interstellar optical polarization data supplemented by the reddening data This compilation includes 13 data sources with optical interstellar linear polarization for 3871 Gaia DR2 and Hipparcos stars within 500pc, which do not exhibit a considerable intrinsic polarization. These data are analysed together with five 3D maps and models of the reddening E(B-V). We consider variations of the polarization degree P, position angle theta, and polarization efficiency P/E(B-V) with Galactic coordinates, distance R, and dereddened colour. P shows a maximum at the Gould Belt mid-plane. P/R drops in the Local Bubble by several times defining a boundary of the Bubble at P=0.1 per cent. All the data sources of the reddening, except Lallement et al., show a drop of P/E(B-V) in the Bubble. The spatial- and colour-dependent variations of P and E(B-V) outside the Bubble compensate each other, resulting in a nearly constant P/E(B-V). A giant envelope of aligned dust dominates at middle and high latitudes outside the Bubble. The Markkanen's cloud, the North Polar Spur, and some other filaments are parts of this envelope.
