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The Influence of Metallicity on Stellar Differential Rotation and Magnetic Activity

C. Karoff, T. S. Metcalfe, A. R. G. Santos, B. T. Montet, H. Isaacson, V Witzke, A. I Shapiro, S. Mathur, G. R. Davies, M. N. Lund, R. A. García, A. S. Brun, D. Salabert, P. P. Avelino, J. L. Van Saders, R. Egeland, M. S. Cunha, T. L. Campante, W. J. Chaplin, N. Krivova, S. K. Solanki, M. Stritzinger, M. F. Knudsen

Abstract
Observations of Sun-like stars over the past half-century have improved our understanding of how magnetic dynamos, like that responsible for the 11 yr solar cycle, change with rotation, mass, and age. Here we show for the first time how metallicity can affect a stellar dynamo. Using the most complete set of observations of a stellar cycle ever obtained for a Sun-like star, we show how the solar analog HD 173701 exhibits solar-like differential rotation and a 7.4 yr activity cycle. While the duration of the cycle is comparable to that generated by the solar dynamo, the amplitude of the brightness variability is substantially stronger. The only significant difference between HD 173701 and the Sun is its metallicity, which is twice the solar value. Therefore, this provides a unique opportunity to study the effect of the higher metallicity on the dynamo acting in this star and to obtain a comprehensive understanding of the physical mechanisms responsible for the observed photometric variability. The observations can be explained by the higher metallicity of the star, which is predicted to foster a deeper outer convection zone and a higher facular contrast, resulting in stronger variability.

Keywords
stars: activity; stars: chromospheres; stars: individual: HD 173701; stars: oscillations: including pulsations; stars: rotation; stars: solar-type; Astrophysics - Solar and Stellar Astrophysics

The Astrophysical Journal
Volume 852, Number 1
2018 January

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia