Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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TEMPORAL VARIATIONS OF THE GLOBAL SEISMIC PARAMETERS OF HD 49933 OVER A MAGNETIC CYCLE

  • Kim, Ki-Beom (Department of Astronomy and Atmospheric Sciences, Kyungpook National University) ;
  • Chang, Heon-Young (Department of Astronomy and Atmospheric Sciences, Kyungpook National University)
  • Received : 2021.05.07
  • Accepted : 2021.07.01
  • Published : 2021.08.31
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Abstract

It has been established that the acoustic mode parameters of the Sun and Sun-like stars vary over activity cycles. Since the observed variations are not consistent with an activity-related origin, even Sun-like stars showing out-of-phase changes of mode frequencies and amplitudes need to be carefully studied using other observational quantities. In order to test whether the presumed relations between the global seismic parameters are a signature of the stellar activity cycle, we analyze the photometric light curve of HD 49933 for which the first direct detection of an asteroseismic signature for activity-induced variations in a Sun-like star was made, using observations by the CoRoT space telescope. We find that the amplitude of the envelope significantly anti-correlates with both the maximum frequency of the envelope and the width of the envelope unless superflare-like events completely contaminate the light curve. However, even though the photometric proxy for stellar magnetic activity appears to show relations with the global asteroseismic parameters, they are statistically insignificant. Therefore, we conclude that the global asteroseismic parameters can be utilized in cross-checking asteroseismic detections of activity-related variations in Sun-like stars, and that it is probably less secure and effective to construct a photometric magnetic activity proxy to indirectly correlate the global asteroseismic parameters. Finally, we seismically estimate the mass of HD 49933 based on our determination of the large separation of HD 49933 with evolutionary tracks computed by the MESA code and find a value of about 1.2M☉ and a sub-solar metallicity of Z = 0.008, which agrees with the current consensus and with asteroseismic and non-asteroseismic data.

Keywords

Acknowledgement

The authors thank the anonymous referees for critical comments and helpful suggestions which greatly improved the original version of the manuscript. This study was funded by the Basic Science Research Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT and Future Planning (2018R1A6A1A06024970). HYC was supported by a National Research Foundation of Korea Grant funded by the Korean government (NRF-2018R1D1A3B070421880).

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