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Signatures of Magnetic Activity: On the Relation between Stellar Properties and p-mode Frequency Variations

A. R. G. Santos, T. L. Campante, W. J. Chaplin, M. S. Cunha, J. L. Van Saders, C. Karoff, T. S. Metcalfe, S. Mathur, R. A. García, M. N. Lund, R. Kiefer, V. Silva Aguirre, G. R. Davies, R. Howe, Y. Elsworth

Abstract
In the Sun, the properties of acoustic modes are sensitive to changes in the magnetic activity. In particular, mode frequencies are observed to increase with increasing activity level. Thanks to CoRoT and Kepler, such variations have been found in other solar-type stars and encode information on the activity-related changes in their interiors. Thus, the unprecedented long-term Kepler photometric observations provide a unique opportunity to study stellar activity through asteroseismology. The goal of this work is to investigate the dependencies of the observed mode frequency variations on the stellar parameters and whether those are consistent with an activity-related origin. We select the solar-type oscillators with highest signal-to-noise ratio, in total, 75 targets. Using the temporal frequency variations determined in Santos et al., we study the relation between those variations and the fundamental stellar properties. We also compare the observed frequency shifts with chromospheric and photometric activity indexes, which are only available for a subset of the sample. We find that frequency shifts increase with increasing chromospheric activity, which is consistent with an activity-related origin of the observed frequency shifts. Frequency shifts are also found to increase with effective temperature, which is in agreement with the theoretical predictions for the activity-related frequency shifts by Metcalfe et al. Frequency shifts are largest for fast rotating and young stars, which is consistent with those being more active than slower rotators and older stars. Finally, we find evidence for frequency shifts increasing with stellar metallicity.

Keywords
asteroseismology; stars: activity; stars: oscillations: including pulsations; stars: solar-type; Astrophysics - Solar and Stellar Astrophysics

The Astrophysical Journal
Volume 883, Number 1, Page 13
2019 September

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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