Temperature condensation trend in the debris-disk binary system Zet2 Reticuli

CARLOS SAFFE; FLORES, M.; MARCELO JAQUE ARANCIBIA; ANDREA BUCCINO; JOFRÉ, E

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2016 vol. 588 p. 1 - 7

0004-6361

Context. Detailed abundance studies have reported different trends between samples of stars with and without planets, possibly relatedto the planet formation process. Whether these differences are still present between samples of stars with and without debris disk isstill unclear.Aims. We explore condensation temperature Tc trends in the unique binary system ζ1 Ret − ζ2 Ret to determine whether there is adepletion of refractories that could be related to the planet formation process. The star ζ2 Ret hosts a debris disk which was detectedby an IR excess and confirmed by direct imaging and numerical simulations, while ζ1 Ret does not present IR excess or planets. Thesecharacteristics convert ζ2 Ret in a remarkable system where their binary nature together with the strong similarity of both componentsallow us, for the first time, to achieve the highest possible abundance precision in this system.Methods. We carried out a high-precision abundance determination in both components of the binary system via a line-by-line, strictlydifferential approach. First we used the Sun as a reference and then we used ζ2 Ret. The stellar parameters Teff , log g, [Fe/H], andv turb were determined by imposing differential ionization and excitation equilibrium of Fe I and Fe II lines, with an updated version ofthe program FUNDPAR, together with plane-parallel local thermodynamic equilibrium ATLAS9 model atmospheres and the MOOGcode. We then derived detailed abundances of 24 different species with equivalent widths and spectral synthesis with the MOOGprogram. The chemical patterns were compared with a recently calculated solar-twins Tc trend, and then mutually between both starsof the binary system. The rocky mass of depleted refractory material was estimated according to recent data.Results. The star ζ1 Ret is found to be slightly more metal rich than ζ2 Ret by ∼0.02 dex. In the differential calculation of ζ1 Ret usingζ2 Ret as reference, the abundances of the refractory elements are higher than the volatile elements, and the trend of the refractoryelements with Tc shows a positive slope. These results together show a lack of refractory elements in ζ2 Ret (a debris-disk host)relative to ζ1 Ret. The Tc trend would be in agreement with the proposed signature of planet formation rather than possible galacticchemical evolution or age effects, which are largely diminished here. Then, following the recent interpretation, we propose a scenarioin which the refractory elements depleted in ζ2 Ret are possibly locked up in the rocky material that orbits this star and produce thedebris disk observed around this object. We estimated a lower limit of M rock ∼ 3 M ⊕ for the rocky mass of depleted material, which iscompatible with rough estimations of 3−50 M ⊕ of a debris disk mass around a solar-type star.