A temperature condensation trend in the debris-disk binary system zet2 Reticuli

SAFFE, C.; FLORES, M.; JAQUE ARANCIBIA, M.; BUCCINO, A. P.; JOFRE, E.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2016 vol. 588 p. 81 - 101

0004-6361

Context. Detailed abundance studies have reported different trendsbetween samples of stars with and without planets, possibly related tothe planet formation process. Whether these differences are stillpresent between samples of stars with and without debris disk is stillunclear. Aims: We explore condensation temperature Tctrends in the unique binary system ζ1 Ret-ζ2 Ret to determine whether there is a depletion ofrefractories that could be related to the planet formation process. Thestar ζ2 Ret hosts a debris disk which was detected by anIR excess and confirmed by direct imaging and numerical simulations,while ζ1 Ret does not present IR excess or planets.These characteristics convert ζ2 Ret in a remarkablesystem where their binary nature together with the strong similarity ofboth components allow us, for the first time, to achieve the highestpossible abundance precision in this system. Methods: We carriedout a high-precision abundance determination in both components of thebinary system via a line-by-line, strictly differential approach. Firstwe used the Sun as a reference and then we used ζ2 Ret.The stellar parameters Teff, log g, [Fe/H], andvturb were determined by imposing differential ionization andexcitation equilibrium of Fe I and Fe II lines, with an updated versionof the program FUNDPAR, together with plane-parallel local thermodynamicequilibrium ATLAS9 model atmospheres and the MOOG code. We then deriveddetailed abundances of 24 different species with equivalent widths andspectral synthesis with the MOOG program. The chemical patterns werecompared with a recently calculated solar-twins Tc trend, andthen mutually between both stars of the binary system. The rocky mass ofdepleted refractory material was estimated according to recent data. Results: The star ζ1 Ret is found to be slightly moremetal rich than ζ2 Ret by ~0.02 dex. In the differentialcalculation of ζ1 Ret using ζ2 Ret asreference, the abundances of the refractory elements are higher than thevolatile elements, and the trend of the refractory elements withTc shows a positive slope. These results together show a lackof refractory elements in ζ2 Ret (a debris-disk host)relative to ζ1 Ret. The Tc trend would be inagreement with the proposed signature of planet formation rather thanpossible galactic chemical evolution or age effects, which are largelydiminished here. Then, following the recent interpretation, we propose ascenario in which the refractory elements depleted in ζ2Ret are possibly locked up in the rocky material that orbits this starand produce the debris disk observed around this object. We estimated alower limit of Mrock ~ 3 M⊕ for the rockymass of depleted material, which is compatible with rough estimations of3-50 M⊕ of a debris disk mass around a solar-type star.