paper

Revisiting the impact of stellar magnetic activity on the detectability of solar-like oscillations by Kepler

arXiv:1907.01415 · doi:10.3389/fspas.2019.00046

Abstract

Over 2,000 stars were observed for one month with a high enough cadence in order to look for acoustic modes during the survey phase of the Kepler mission. Solar-like oscillations have been detected in about 540 stars. The question of why no oscillations were detected in the remaining stars is still open. Previous works explained the non-detection of modes with the high level of magnetic activity. However, the studied stars contained some classical pulsators and red giants that could have biased the results. In this work, we revisit this analysis on a cleaner sample of 1,014 main-sequence solar-like stars. First we compute the predicted amplitude of the modes. We find that the stars with detected modes have an amplitude to noise ratio larger than 0.94. We measure reliable rotation periods and the associated photometric magnetic index for 684 stars and in particular for 323 stars where the mode amplitude is predicted to be high enough to be detected. We find that among these 323 stars 32% have a magnetic activity level larger than the Sun at maximum activity, explaining the non-detection of p modes. Interestingly, magnetic activity cannot be the primary reason responsible for the absence of detectable modes in the remaining 68% of the stars without p modes detected and with reliable rotation periods. Thus, we investigate metallicity, inclination angle, and binarity as possible causes of low mode amplitudes. Using spectroscopic observations for a subsample, we find that a low metallicity could be the reason for suppressed modes. No clear correlation with binarity nor inclination is found. We also derive the lower limit for our photometric activity index (of 20-30 ppm) below which rotation and magnetic activity are not detected. Finally with our analysis we conclude that stars with a photometric activity index larger than 2,000 ppm have 98.3% probability of not having oscillations detected.

Paper Accepter for publication in Frontiers Astronomy and Space Sciences. 31 pages and 15 figures

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