High-precision abundances of elements in solar twin stars - Trends with stellar age and elemental condensation temperature

By P. Nissen. 2015

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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, TC, 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 TC 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. 8G yr) stellar ages are obtained by interpolating between Yonsei-Yale isochrones in the log g ‐ Teff 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]-TC distribution as the Sun), but for many stars, the relation between [X/Fe] and TC is not well defined. For several elements there is an astonishingly tight correlation between [X/Fe] and stellar age with amplitudes up to ∼0.20 dex over an age interval of eight Gyr in contrast to the lack of correlation between [Fe/H] and age. While [Mg/Fe] increases with age, the s-process element yttrium shows the opposite behavior meaning that [Y/Mg] can be used as a sensitive chronometer for Galactic evolution. The Na/Fe and Ni/Fe ratios are not well correlated with stellar age, but define a tight Ni‐Na relation similar to that previously found for more metal-poor stars albeit with a smaller amplitude. Furthermore, the C/O ratio evolves very little with time, although [C/Fe] and [O/Fe] change by ∼0.15 dex. Conclusions. The dependence of [X/Fe] on stellar age and the [Ni/Fe]‐ [Na/Fe] variations complicate the use of the [X/Fe]-TC relation as a possible signature for the existence of terrestrial planets around stars. The age trends for the various abundance ratios provide new constraints on supernovae yields and Galactic chemical evolution, and the slow evolution of C/O for solar metallicity stars is of interest for discussions of the composition of exoplanets.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a2a27c5a5a07efaa54aece4b126653881a959cdf

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Citations in the corpus

The GALAH+ survey: Third data release (2020, background): “For such stars, these and other studies (e.g. Nissen 2015) have found tight correlations with abundances and stellar ages, that is, chemical clocks.”
Dissecting stellar chemical abundance space with t-SNE (2018, background): “…of the immediate solar vicinity (e.g. Edvards-son et al. 1993; Fuhrmann 1998, 2011; Fuhrmann et al. 2017; Adibekyan et al. 2012; Bensby et al. 2014; Nissen 2015, 2016; Delgado Mena et al. 2017) remain at least equally important for Galactic Archaeology (see Lindegren & Feltzing 2013 for a…”
Stellar ages and masses in the solar neighbourhood: Bayesian analysis using spectroscopy and Gaia DR1 parallaxes (2018, methodology): “In this Section we present the comparison between our derived stellar ages and masses with literature values for the B14, R12, N15, T16 and C11 samples; the A12 sample is discussed in Section 4.2 as they did not provide age/mass estimates themselves.”