Temperature condensation trend in the debris-disk binary system ζ2 Reticuli⋆
Instituto de Ciencias Astronómicas,
de la Tierra y del Espacio (ICATE-CONICET), CC
e-mail: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org
2 Universidad Nacional de San Juan (UNSJ), Facultad de Ciencias Exactas, Físicas y Naturales (FCEFN), 5400 San Juan, Argentina
3 Instituto de Astronomía y Física del Espacio (IAFE-CONICET), 1428 Buenos Aires, Argentina
4 Departamento de Física, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
5 Observatorio Astronómico de Córdoba (OAC), Laprida 854, X5000BGR, Córdoba, Argentina
6 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 1428 Buenos Aires, Argentina
Received: 24 December 2015
Accepted: 2 February 2016
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 Tc trends in the unique binary system ζ1 Ret −ζ2 Ret to determine whether there is a depletion of refractories that could be related to the planet formation process. The star ζ2 Ret hosts a debris disk which was detected by an IR 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 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 ζ2 Ret. The stellar parameters Teff, log g, [Fe/H], and vturb 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 Tc 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 ζ1 Ret is found to be slightly more metal rich than ζ2 Ret by ~0.02 dex. In the differential calculation of ζ1 Ret using ζ2 Ret as reference, the abundances of the refractory elements are higher than the volatile elements, and the trend of the refractory elements 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 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 ζ2 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 Mrock ~ 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.
Key words: stars: abundances / planetary systems / binaries: general / stars: individual: ζ1Ret / stars: individual: ζ2Ret
Tables 1 and 3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A81
© ESO, 2016