Temperature condensation trend in the debris-disk binary systemζ²Reticuli

Abstract

Context. Detailed abundance studies have reported different trends between samples of stars with and without planets, possibly related to the planet formation process. Whether these differences are still present between samples of stars with and without debris disk is still unclear. Aims. We explore condensation temperature T c trends in the unique binary system ζ 1 Ret − ζ 2 Ret to determine whether there is a depletion of refractories that could be related to the planet formation process. The star ζ 2 Ret hosts a debris disk which was detected by an IR excess and confirmed by direct imaging and numerical simulations, while ζ 1 Ret does not present IR excess or planets. These characteristics convert ζ 2 Ret in a remarkable system where their binary nature together with the strong similarity of both components allow 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, strictly differential approach. First we used the Sun as a reference and then we used ζ 2 Ret. The stellar parameters T eff , log g, [Fe/H], and v turb were determined by imposing differential ionization and excitation equilibrium of Fe I and Fe II lines, with an updated version of the program FUNDPAR, together with plane-parallel local thermodynamic equilibrium ATLAS9 model atmospheres and the MOOG code. We then derived detailed abundances of 24 different species with equivalent widths and spectral synthesis with the MOOG program. The chemical patterns were compared with a recently calculated solar-twins T c trend, and then mutually between both stars of the binary system. The rocky mass of depleted refractory material was estimated according to recent data. Results. The star ζ 1 Ret is found to be slightly more metal rich than ζ 2 Ret by ∼0.02 dex. In the differential calculation of ζ 1 Ret using ζ 2 Ret as reference, the abundances of the refractory elements are higher than the volatile elements, and the trend of the refractory elements with T c shows a positive slope. These results together show a lack of refractory elements in ζ 2 Ret (a debris-disk host) relative to ζ 1 Ret. The T c trend would be in agreement with the proposed signature of planet formation rather than possible galactic chemical evolution or age effects, which are largely diminished here. Then, following the recent interpretation, we propose a scenario in which the refractory elements depleted in ζ 2 Ret are possibly locked up in the rocky material that orbits this star and produce the debris disk observed around this object. We estimated a lower limit of M rock ∼ 3 M ⊕ for the rocky mass of depleted material, which is compatible with rough estimations of 3−50 M ⊕ of a debris disk mass around a solar-type star.

Abundance trend with condensation temperature for stars with different Galactic birth places

“…This very exciting and important (possible) connection between chemical peculiarities and formation of planets has also been examined in other works (e.g. Takeda et al 2001;Ecuvillon et al 2006;Sozzetti et al 2006;Schuler et al 2011b;González Hernández et al 2013;Maldonado et al 2015;Nissen 2015;Biazzo et al 2015;Saffe et al 2015Saffe et al , 2016, but contradictory conclusions were reached.…”

“…The main reason for using [X/Fe] instead of [X/H] is to be able to remove the trends related to the Galactic chemical evolution (GCE) from the [X/Fe]−[Fe/H] relations (e.g. González Hernández et al 2013;Saffe et al 2016;Liu et al 2016). Recently, some authors used the [X/Fe]−age relation to correct for the GCE (e.g.…”

“…Very recently, Saffe et al (2016) reported a positive T c trend in the binary system ζ 1 Ret -ζ 2 Ret, where one of the stars (ζ 2 Ret) hosts a debris disk. The deficit of the refractory elements relative to volatiles in ζ 2 Ret was explained by the authors as being caused by the depletion of about ∼3 M ⊕ rocky material.…”

ζ2Reticuli, its debris disk, and its lonely stellar companionζ1Ret

“…The 50% T c equilibrium condensation temperatures for a gas of solar system composition are taken from Lodders (2003). It is common practice to plot [X/Fe] (and not just [X/H]) versus T c , which allows us to remove the trends related to Galactic chemical evolution (e.g., González Hernández et al 2013;Saffe et al 2016). Although this procedure can be justified when stars with different metallicities are compared, it can produce a bias in the derived slope.…”

Signatures of rocky planet engulfment in HAT-P-4

“…Several studies have shown that there may be small differences in the chemical composition of their components, possibly due to the planet formation process (Gratton et al 2001;Desidera et al 2004Desidera et al , 2006. The similarity between the two components of a binary system enabled achieving a higher precision in a differential study (e.g., Saffe et al 2015Saffe et al , 2016. To date, more than 2700 planetary systems have been reported 2 , but only a handful of these systems are binaries with similar components.…”