Ionization balance of Ti in the photospheres of the Sun and four late-type stars

Bergemann, M.

doi:10.1111/j.1365-2966.2011.18295.x

Cited by 124 publications

(141 citation statements)

References 68 publications

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“…A Ni-Na relation has, however, been found for thick-disk and halo stars with −1.6 < [Fe/H] − 0.4 (Nissen & Schuster 1997, 2010, 2011 and for stars in dwarf spheroidal galaxies in the same metallicity interval (Venn et al 2004;Letarte 2010;Lemasle 2014). For these metal-poor stars, the amplitude of the variations is larger (∼0.…”

Section: Discussionmentioning

confidence: 95%

High-precision abundances of elements in solar twin stars

Nissen

2015

A&A

254

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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Section: Discussionmentioning

confidence: 95%

High-precision abundances of elements in solar twin stars

Nissen

2015

A&A

254

304

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“…We refer to Paper V for a more detailed discussion. The abundances for neutral Ti I are not used here to avoid non-LTE effects that cause an ionization imbalance in this species, as shown by Bergemann (2011) and Bergemann & Nordlander (2014). It is noteworthy that the correction of +0.25 dex for Ti I, suggested by Bergemann (2011) and based on the metal-poor RGB star HD 122563 ([Fe/H] = −2.5), agrees very well with the difference we found in our stars Ti I-Ti II = +0.28 dex.…”

Section: Comparison With the Galactic Halomentioning

confidence: 99%

The Carina Project

Fabrizio

Nonino

Bono

et al. 2015

A&A

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We have performed a new abundance analysis of Carina red giant (RG) stars from spectroscopic data collected with UVES (high spectral resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high-resolution) and ∼800 (medium-resolution) RGs, covering a significant fraction of the galaxy's RG branch, and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins. The spectra of the stars belonging to the same gravity and temperature bin were stacked. This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit (V ≥ 20.5 mag) by at least a factor of five. We took advantage of the new photometry index c U,B,I introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean iron abundances are −2.15 ± 0.06 dex (σ = 0.28), and −1.75 ± 0.03 dex (σ = 0.21), respectively. The two iron distributions differ at the 75% level. This supports preliminary results. Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of −1.91 ± 0.05 dex (σ = 0.22) and −1.35 ± 0.03 dex (σ = 0.22); these differ at the 83% level. Carina's α-element abundances agree, within 1σ, with similar abundances for field halo stars and for cluster (Galactic and Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite different from that in the globular clusters.

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“…Sgr field stars are indicated for previous works: filled gray circles (Carretta et al 2010;C10), filled red circles (Smecker-Hane & McWilliam 2002;SM02), filled and open blue circles (Bonifacio et al 2000(Bonifacio et al , 2004B00;B04), and filled magenta squares (Sbordone et al 2007;S07 We note that a long-known disparity between Ti i and Ti ii abundances may have contributed to the low [Ti/Fe] ratios in S07 and other papers. The cause of the Ti ionization imbalance has recently been shown to be due to non-LTE effects on Ti i by Bergemann (2011). Bergemann (2011) finds that Ti i non-LTE corrections of + 0.25 dex are required for the very metal-poor RGB star HD 122563 ([Fe/H] = −2.5); whether the correction would be similar for solar-metallicity RGB stars is not known.…”

Section: Ironmentioning

confidence: 99%