A temperature condensation trend in the debris-disk binary system ζ2 Ret

Abstract

We explore condensation temperature Tc trends in the unique binary systemZet1 Ret - Zet2 Ret, to determine whether there is a depletion of refractories,which could be related to the planet formation process. The star Zet2 Ret hostsa debris disk which was detected by an IR excess and confirmed by directimaging and numerical simulations, while Zet1 Ret does not present IR excessnor planets. We carried out a high-precision abundance determination in bothcomponents of the binary system via a line-by-line, strictly differentialapproach. The stellar parameters Teff , log g, [Fe/H] and vturb were determinedby imposing differential ionization and excitation equilibrium of Fe I and FeII lines, with an updated version of the program FUNDPAR. The star Zet1 Retresulted slightly more metal rich than Zet2 Ret by 0.02 dex. In thedifferential calculation of Zet1 Ret using Zet2 Ret as reference, theabundances of the refractory elements resulted higher than the volatileelements, and the trend of the refractory elements with Tc showed a positiveslope. These facts together show a lack of refractory elements in Zet2 Ret (adebris-disk host) relative to Zet1 Ret. The Tc trend would be in agreement withthe proposed signature of planet formation (Melendez et al. 2009) rather thanpossible Galactic Chemical Evolution or age effects, which are largelydiminished here. Then, following the interpretation of Melendez et al. (2009),we propose an scenario in which the refractory elements depleted in Zet2 Retare possibly locked-up in the rocky material that orbits this star and producethe debris disk observed around this object. We estimated a lower limit ofMrock = 3 Me for the rocky mass of depleted material, which is compatible witha rough estimation of 3-50 Me of a debris disk mass around a solar-type star.