ζ 1 + ζ 2 Reticuli binary system: A puzzling chromospheric activity pattern

M. FLORES; C. SAFFE; A. BUCCINO; M. JAQUE ARANCIBIA; J.F. GONZÁLEZ; N. E. NUÑEZ; E. JOFRÉ

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 476

0035-8711

We perform, for the first time, a detailed long-term activity study of the binary system ζ Ret. We use all available HARPS spectra obtained between the years 2003 and 2016.We built a time series of the Mount Wilson S index for both stars, then we analyse these series by using Lomb-Scargle periodograms. The components ζ 1 Ret and ζ 2 Ret that belong to this binary system are physically very similar to each other and also similar to our Sun, which makes it a remarkable system. We detect in the solar- analogue star ζ 2 Ret a long-term activity cycle with a period of ∼10 yr, similar to the solar one (∼11 yr). It is worthwhile to mention that this object satisfies previouscriteria for a flat star and for a cycling star simultaneously. Another interesting feature of this binary system, is a high ∼0.220 dex difference between the averages log(R 0 HK ) activity levels of both stars. Our study clearly shows that ζ 1 Ret is significantly more active than ζ 2 Ret. In addition, ζ 1 Ret shows an erratic variability in its stellar activity.In this work, we explore different scenarios trying to explain this rare behaviour in a pair of coeval stars, which could help to explain the difference in this and other binary systems. From these results, we also warn that for the development of activity-age calibrations (which commonly use binary systems and/or stellar clusters as calibrators) it should be taken into account the whole history of activity available of the stars involved.