A New Method for Estimating Starspot Lifetimes Based on Autocorrelation Functions

Abstract

We present a method that utilizes autocorrelation functions from long-term precision broadband differential light curves to estimate the average lifetimes of starspot groups for two large sample of Kepler stars: stars with and without previously known rotation periods. Our method is calibrated by comparing the strengths of the first few normalized autocorrelation peaks using ensembles of models that have various starspot lifetimes. We find that we must mix models of short and long lifetimes together (in heuristically determined ratios) to align the models with the Kepler data. Our fundamental result is that short starspot group lifetimes (1-4 rotations) are implied when the first normalized peak is weaker than about 0.4, long lifetimes (15 or greater) are implied when it is greater than about 0.7, and in between are the intermediate cases. Rotational lifetimes can be converted to physical lifetimes if the rotation period is known. Stars with shorter rotation periods tend to have longer rotational (but not physical) spot lifetimes, and cooler stars tend to have longer physical spot lifetimes than warmer stars with the same rotation period. The distributions of the physical lifetimes are lognormal for both samples and generally longer in the first sample. The shorter lifetimes in the stars without known periods probably explain why their periods are difficult to measure. Some stars exhibit longer than average physical starspot lifetimes; their percentage drops with increasing temperature from nearly half at 3000K to nearly zero for hotter than 6000K.

60 pages, 18 figures, refereed, to be published in ApJ

References in corpus (11)

• Testing the recovery of stellar rotation signals from Kepler light curves using a blind hare-and-hounds exercise
• A Kepler Study of Starspot Lifetimes with Respect to Light Curve Amplitude and Spectral Type
• The Sun is less active than other solar-like stars
• Evidence for photometric activity cycles in 3203 Kepler stars
• Looking for activity cycles in late-type Kepler stars using time-frequency analysis
• On Sunspot and Starspot Lifetimes
• Starspot signature on the light curve: Learning about the latitudinal distribution of spots
• Short-period stellar activity cycles with Kepler photometry
• Starspot rotation rates vs. activity cycle phase: Butterfly diagrams of Kepler stars are unlike the Sun's
• On the relation between active-region lifetimes and the autocorrelation function of light curves
• New Suns in the Cosmos II: Differential rotation in Kepler Sun-like stars

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• The GAPS programme at TNG XXXIV. Activity-rotation, flux-flux relationships, and active region evolution through stellar age
• The breakdown of current gyrochronology as evidenced by old coeval stars
• Measuring periods in aperiodic light curves -- Applying the GPS method to infer rotation periods of solar-like stars
• Infrared variability of young solar analogs in the Lagoon Nebula
• The changing transit shape of TOI-3884 b
• Flaring Latitudes in Ensembles of Low Mass Stars
• Activity of low mass stars in the light of spot signature in the Fourier domain
• Exploring Young Stellar Variability with Gaia DR3 light curves
• Transit Hunt for Young and Maturing Exoplanets (THYME) VIII: a Pleiades-age association harboring two transiting planetary systems from Kepler
• Characterisation of starspot structure and differential rotation of Kepler-411
• SpinSpotter: An Automated Algorithm for Identifying Stellar Rotation Periods With Autocorrelation Analysis
• Characterising the stellar differential rotation based on largest-spot statistics from ground-based photometry