Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach
نویسندگان
چکیده
We explore subtle variations in disk-integrated measurements spanning ∼ 18 years of stellar surface magnetism by using a newly developed time-frequency gapped wavelet algorithm. We present results based on analysis of the Mount Wilson Ca II H and K emission fluxes in four, magnetically-active stars (HD 1835 [G2V], 82885 [G8IV-V], 149661 [K0V] and 190007 [K4V]) and sensitivity tests using artificial data. When the wavelet basis is appropriately modified (i.e., when the timefrequency resolution is optimized), the results are consistent with the existence of spatially localized and long-lived Ca II features (assumed here as activity regions that tend to recur in narrowly-confined latitude bands), especially in HD 1835 and 82885. This interpretation is based on the observed persistence of relatively localized Ca II wavelet power at a narrow range of rotational time scales, enduring as long as > ∼ 10 years. Subject headings: numerical methods — stars: chromospheres — stars: rotation
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