zeta1 + zeta2 Reticuli binary system: A puzzling chromospheric activity pattern

FLORES, MATÍAS; SAFFE, CARLOS; BUCCINO, A.; JAQUE ARANCIBIA, M.; GONZALEZ, FEDERICO; NUÑEZ, NATALIA; JOFRÉ, E.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 476 p. 2751 - 2759

0035-8711

We perform, for the first time, a detailed long-term activity study of the binary system Zeta 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 zeta1 Ret and zeta2 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 zeta2 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 previous criteria 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(RHK) activity levels of both stars. Our study clearly shows that zeta1 Ret is significantly more active than zeta2 Ret. In addition, zeta1 Ret shows an erratic variability in its stellar activity. In this work, we explore different scenarios trying to explain this rare behaviour in apair 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.