Discovery of an activity cycle in the solar analog HD 45184. Exploring Balmer and metallic lines as activity proxy candidates

FLORES, M. G.; GONZÁLEZ, J.F.; JAQUE ARANCIBIA, M.; BUCCINO, A.; SAFFE, C.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2016 vol. 589 p. 1 - 6

0004-6361

Context. Most stellar activity cycles similar to that found in the Sunhave been detected by using the chromospheric Ca ii H&K lines asstellar activity proxies. However, it is unclear whether such activitycycles can be identified using other optical lines. Aims: We aimto detect activity cycles in solar-analog stars and determine whetherthey can be identified through other optical lines, such as Fe II andBalmer lines. We study the solar-analog star HD 45184 using HARPSspectra. The temporal coverage and high quality of the spectra allow usto detect both long- and short-term activity variations. Methods:We analysed the activity signatures of HD 45184 by using 291 HARPSspectra obtained between 2003 and 2014. To search for line-core fluxvariations, we focused on Ca ii H&K and Balmer Hα and Hβlines, which are typically used as optical chromospheric activityindicators. We calculated the HARPS-S index from Ca ii H&K lines andconverted it into the Mount Wilson scale. In addition, we alsoconsidered the equivalent widths of Balmer lines as activity indicators.Moreover, we analysed the possible variability of Fe ii and othermetallic lines in the optical spectra. The spectral variations wereanalysed for periodicity using the Lomb-Scargle periodogram. Results: We report for the first time a long-term 5.14-yr activity cyclein the solar-analog star HD 45184 derived from Mount Wilson S index.This makes HD 45184 one of most similar stars to the Sun with a knownactivity cycle. The variation is also evident in the first lines of theBalmer series, which do not always show a correlation with activity insolar-type stars. Notably, unlike the solar case, we also found that theequivalent widths of the high photospheric Fe ii lines (4924 Å,5018 Å and 5169 Å) are modulated (±2 mÅ) by thechromospheric cycle of the star. These metallic lines show variationsabove 4σ in the rms spectrum, while some Ba ii and Ti ii linespresent variations at 3σ level, which could be considered asmarginal variations. From short-term modulation of the S index wecalculate a rotational period of 19.98 days, which agrees with its meanchromospheric activity level. We also clearly show that the activitycycles of HD 45184 can be detected in both Fe ii and Balmer lines.