ζ² Reticuli, its debris disk, and its lonely stellar companion ζ¹ Ret

Different T_c trends for different spectra^⋆,⋆⋆

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: Vardan.Adibekyan@astro.up.pt
² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³ Instituto de Astrofísica de Canarias, 38200, La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, 38206, La Laguna, Tenerife, Spain
⁵ Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Byurakan Astrophysical Observatory, 0213 Byurakan, Aragatsotn province, Armenia

Received: 7 March 2016
Accepted: 24 April 2016

Abstract

Context. Several studies have reported a correlation between the chemical abundances of stars and condensation temperature (known as T_c trend). Very recently, a strong T_c trend was reported for the ζ Reticuli binary system, which consists of two solar analogs. The observed trend in ζ² Ret relative to its companion was explained by the presence of a debris disk around ζ² Ret.

Aims. Our goal is to re-evaluate the presence and variability of the T_c trend in the ζ Reticuli system and to understand the impact of the presence of the debris disk on a star.

Methods. We used very high-quality spectra of the two stars retrieved from the HARPS archive to derive very precise stellar parameters and chemical abundances. We derived the stellar parameters with the classical (nondifferential) method, while we applied a differential line-by-line analysis to achieve the highest possible precision in abundances, which are fundamental to explore for very tiny differences in the abundances between the stars.

Results. We confirm that the abundance difference between ζ² Ret and ζ¹ Ret shows a significant (~2σ) correlation with T_c. However, we also find that the T_c trends depend on the individual spectrum used (even if always of very high quality). In particular, we find significant but varying differences in the abundances of the same star from different individual high-quality spectra.

Conclusions. Our results for the ζ Reticuli system show, for example, that nonphysical factors, such as the quality of spectra employed and errors that are not accounted for, can be at the root of the T_c trends for the case of individual spectra.