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Analyzing the Chromospheric Activity of FGK Dwarfs From the Dharma Planet Survey

Published onJun 01, 2020
Analyzing the Chromospheric Activity of FGK Dwarfs From the Dharma Planet Survey

By using two well-known activity indicators such as the Hα line and the Ca IRT lines, we look forward to measuring both magnetic cycles and stellar rotation periods for FGK type stars, and any correlation between these two activity indicators. Our data was taken from the Dharma Planet Survey, and this is the first in-depth analysis of stellar activity coming from this survey. We analyze a sample of 23 stars and by computing the long-term variability we expect to detect the magnetic cycles of these stars. By using the F-test, we measure the significance in the variability. Any associated P-values less than 5% with the F-tests are considered to be significant. By computing the Pearson Correlation Coefficient, we studied the correlation between both activity indicators. The chosen significance level was 5% for the coefficient value. Finally, we measured the rotation period using the Lomb-Scargle Periodogram. The significance on the peaks were considered using FAP less than 5%. Our observation time span is not long enough to cover for whole magnetic cycles. We were only able to detect three different phases of these cycles: Active, Quiet, or Transition phases. For significant long-term variability, 8 stars from the sample show significant variability for the Hα index and 12 stars for the Ca IRT index. We then noticed that the index correlation is mainly influenced by the magnetic cycle phase, instead of the variability significance. For the PCC, we have values ranging from -0.3 to 0.3 and 9 stars showing significant correlation coefficients. Finally, we were able to detect four different rotation phases: Significant, Not Significant, Stable, and Immeasurable. These phases are based on the FAP values from the Lomb-Scargle periodogram. In addition, considering both activity indicators, we were able to measure the rotation period of 12 stars. The most remarkable result is shown on the star HD115043, for which we measured a rotation period of ~6 days in both activity indicators. These measurements match the values from the literature.

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