Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach
1998
We explore subtle variations in disk-integrated measurements spanning
$\lsim$ 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 time-frequency 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 $\gsim$ 10 years.
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