Two distinct halo populations in the solar neighborhood

Nissen, P. E.; Schuster, W. J.

doi:10.1051/0004-6361/201219342

Cited by 34 publications

(22 citation statements)

References 59 publications

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“…We also compare our results for 47 Tuc with those obtained in the recent investigation of Nissen & Schuster (2012) who measured lithium abundances in a sample of halo stars in the metallicity range −1.4 < [Fe/H] < −0.7. In terms of [Fe/H], 47 Tuc is therefore just on the edge of this sample, although it is well within the Z range (see below).…”

Section: Comparison With the Halo Field Starssupporting

confidence: 52%

“…It may be interesting to note that the linear relations of Nissen & Schuster (2012) cannot be extrapolated to lower metallicities, since they would predict higher Li abundances than those observed in field stars, as is nicely demonstrated by their Fig. 7.…”

Section: Comparison With the Halo Field Starsmentioning

confidence: 90%

“…Qualitatively, this result is indeed expected, because of the deepening of the convective envelope for less massive and more metal rich stars that is predicted by models of stellar evolution. On the Z scale adopted by Nissen & Schuster (2012), based on Table 2 of Kim et al (2002), 47 Tuc has Z = 0.00396.…”

Section: Comparison With the Halo Field Starsmentioning

confidence: 99%

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Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tucanae

Dobrovolskas

Kučinskas

Bonifacio

et al. 2014

A&A

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Context. The cluster 47 Tuc is among the most metal-rich Galactic globular clusters and its metallicity is similar to that of metal-poor disc stars and open clusters. Like other globular clusters, it displays variations in the abundances of elements lighter than Si, which is generally interpreted as evidence of the presence of multiple stellar populations. Aims. We aim to determine abundances of Li, O, and Na in a sample of of 110 turn-off (TO) stars, in order to study the evolution of light elements in this cluster and to put our results in perspective with observations of other globular and open clusters, as well as with field stars. Methods. We use medium resolution spectra obtained with the GIRAFFE spectrograph at the ESO 8.2 m Kueyen VLT telescope and use state of the art 1D model atmospheres and NLTE line transfer to determine the abundances. We also employ CO 5 BOLD hydrodynamical simulations to assess the impact of stellar granulation on the line formation and inferred abundances. Results. Our results confirm the existence of Na-O abundance anti-correlation and hint towards a possible Li-O anti-correlation in the TO stars of 47 Tuc. At the same time, we find no convincing evidence supporting the existence of Li-Na correlation. The obtained 3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were detected reliably, A(Li) 3D NLTE = 1.78 ± 0.18 dex, appears to be significantly lower than what is observed in other globular clusters. At the same time, star-to-star spread in Li abundance is also larger than seen in other clusters. The highest Li abundance observed in 47 Tuc is about 0.1 dex lower than the lowest Li abundance observed among the un-depleted stars of the metal-poor open cluster NGC 2243. Conclusions. The correlations/anti-correlations among light element abundances confirm that chemical enrichment history of 47 Tuc was similar to that of other globular clusters, despite the higher metallicity of 47 Tuc. The lithium abundances in 47 Tuc, when put into context with observations in other clusters and field stars, suggest that stars that are more metal-rich than [Fe/H] ∼ −1.0 experience significant lithium depletion during their lifetime on the main sequence, while the more metal-poor stars do not. Rather strikingly, our results suggest that initial lithium abundance with which the star was created may only depend on its age (the younger the star, the higher its Li content) and not on its metallicity.

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Section: Comparison With the Halo Field Starssupporting

confidence: 52%

Section: Comparison With the Halo Field Starsmentioning

confidence: 90%

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Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tucanae

Dobrovolskas

Kučinskas

Bonifacio

et al. 2014

A&A

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“…Hipparcos parallaxes (van Leeuwen 2007) were used to derive absolute visual magnitudes from V magnitudes based on Strömgren photometry (Olsen 1983), and bolometric corrections were adopted from Casagrande et al (2010). Stellar masses were obtained by interpolating in the luminositylog T eff diagram between the Yonsei-Yale evolutionary tracks of Yi et al (2003); see Nissen & Schuster (2012) for details. The estimated error of log g (phot.)…”

Section: Spectral Linesmentioning

confidence: 99%

High-precision abundances of elements in solar twin stars

Nissen

2015

A&A

Self Cite

256

304

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Context. High-precision determinations of abundances of elements in the atmospheres of the Sun and solar twin stars indicate that the Sun has an unusually low ratio between refractory and volatile elements. This has led to the suggestion that the relation between abundance ratios, [X/Fe], and elemental condensation temperature, T C , can be used as a signature of the existence of terrestrial planets around a star. Aims. HARPS spectra with S /N 600 for 21 solar twin stars in the solar neighborhood and the Sun (observed via reflected light from asteroids) are used to determine very precise (σ ∼ 0.01 dex) differential abundances of elements in order to see how well [X/Fe] is correlated with T C and other parameters such as stellar age. Methods. Abundances of C, O, Na, Mg, Al, Si, S, Ca, Ti, Cr, Fe, Ni, Zn, and Y are derived from equivalent widths of weak and medium-strong spectral lines using MARCS model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Non-LTE effects are considered and taken into account for some of the elements. In addition, precise (σ 0.8 Gyr) stellar ages are obtained by interpolating between Yonsei-Yale isochrones in the log g -T eff diagram. Results. It is confirmed that the ratio between refractory and volatile elements is lower in the Sun than in most of the solar twins (only one star has the same [X/Fe]-T C distribution as the Sun), but for many stars, the relation between [X/Fe] and T C is not well defined.

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“…Some models claim a rotational mixing mechanism and predict stronger Li depletion for planet-hosting stars (Bouvier 2008;Israelian et al 2009;Eggenberger et al 2012). Thus, the Li abundance is an effective indicator of mixing processes in stars and therefore spectroscopic observations of Li in metal-poor stars (including relatively old solar-type stars) are needed (Canto Martins et al 2011;Pace et al 2012;Nissen & Schuster 2012).…”

Section: Introductionmentioning

confidence: 99%

Li I spectra in the 4.65–8.33 micron range: high-Lstates and oscillator strengths

Civiš

Ferus

Kubelík

et al. 2012

A&A

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Context. Infrared (IR) astronomy capacities have rapidly developed in recent years thanks to several ground-and space-based facilities. To take advantage of these capabilities efficiently, a large amount of atomic data (such as line wavenumber, excited-level energy values, and oscillator strengths) are needed. These data are incomplete, in particular, for lithium whose abundances are important for several astrophysical problems. Aims. No laboratory-measured spectra of Li I have been reported for wavelengths longward of 6.6 microns. We aim to find new Li I lines in the 4.65-8.33 microns range due to transitions between states with high orbital momentum (l ≥ 4) and to determine the excitation energies of these states. Methods. The Li I lines were studied using the time-resolved Fourier transform infrared spectroscopy of a plasma created by the laser ablation of a LiF target in a vacuum. The classification of the lines was performed by accounting for oscillator strengths ( f -values) calculated using quantum defect theory (QDT). The adequacy of QDT for these calculations was checked by comparison with the available experimental and theoretical results. Results. We report four new Li I lines in the 900-2200 cm -1 range that allow us to extract the excitation energies of the 6g, 6h, and 7h states of Li I, which have not been measured before. We also provide a large list of QDT-calculated f -values for Li I in the range of 1-20 microns.

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Two distinct halo populations in the solar neighborhood

Cited by 34 publications

References 59 publications

Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tucanae

Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tucanae

High-precision abundances of elements in solar twin stars

Li I spectra in the 4.65–8.33 micron range: high-Lstates and oscillator strengths

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