Abundance study of the two solar-analogue CoRoT targets HD 42618 and HD 43587 from HARPS spectroscopy

Abstract

We present a detailed abundance study based on spectroscopic data obtained with HARPS of two solar-analogue main targets for the asteroseismology programme of the CoRoT satellite: HD 42618 and HD 43587. The atmospheric parameters and chemical composition are accurately determined through a fully differential analysis with respect to the Sun observed with the same instrumental set-up. Several sources of systematic errors largely cancel out with this approach, which allows us to narrow down the 1-σ error bars to typically 20 K in effective temperature, 0.04 dex in surface gravity, and less than 0.05 dex in the elemental abundances. Although HD 42618 fulfils many requirements for being classified as a solar twin, its slight deficiency in metals and its possibly younger age indicate that, strictly speaking, it does not belong to this class of objects. On the other hand, HD 43587 is slightly more massive and evolved. In addition, marked differences are found in the amount of lithium present in the photospheres of these two stars, which might reveal different mixing properties in their interiors. These results will put tight constraints on the forthcoming theoretical modelling of their solar-like oscillations and contribute to increase our knowledge of the fundamental parameters and internal structure of stars similar to our Sun.

Seismic analysis of HD 43587Aa, a solar-like oscillator in a multiple system

“…Using ν max = 2247 ± 15 μHz, Δν ν max = 106.8 ± 0.2 μHz from our analysis, T eff = 5947 ± 17 K from Morel et al (2013), and with ν ref = 3104 μHz, and Δν ref = 138.8 μHz from Mosser et al (2013), we obtained a seismic estimation of the mass and of the radius of HD 43587:…”

“…MARCS models were also used for checking, leading to very minor differences. Morel et al (2013) obtained the following properties for HD 43587: T eff = 5947 ± 17 K, log g = 4.37 ± 0.04, and [Fe/H] = −0.02 ± 0.02. The uncertainties take statistical and systematic errors into account.…”

“…Three high signal-to-noise ratio spectra (S/N = 410, 390, and 320) were obtained in December 2010 and January 2011 in the framework of the European Southern Observatory (ESO) LP185.D-0056. Solar spectra taken with the High Accuracy Radial velocity Planet Searcher (HARPS) were also used as reference for the subsequent local thermodynamic equilibrium abundance analysis, performed using the MOOG software and Kurucz atmospheric models with updated opacity distribution functions were used by Morel et al (2013) to analyse these data. MARCS models were also used for checking, leading to very minor differences.…”

“…This quasi-monotonically decreasing PDF confirms the difficulty we had reaching a conclusion and favours rather a small value of v sin (i), be ∼0.5 km s −1 (median value) consistent with the spectroscopic reported in Sect. 2.1 (Morel et al 2013). Two configurations are possible: either the star is seen at a very low inclination, and the rotational splitting is close to 1 μHz, or the splitting is too small to be resolved in the spectrum.…”

“…Recently, Morel et al (2013) published a rather precise value, based on new data: T eff = 5947±17 K (more details are given in Sect. 2.1).…”