From the impact of stellar spots in photometry to new observational constraints on the dynamo

The mechanisms behind stellar magnetism remain an open question in stellar physics: there is a huge variety of topologies and magnetic properties and scales. The link between these properties and stellar parameters (radius, mass, age, temperature, or Rossby number) is still elusive. The photometric activity is used here as an observable to improve our understanding of spot characteristics (area, lifetime etc.) and link these properties to the dynamo effect which rules all these phenomena. We propose to characterize this activity using the signature of spots in the light curves, seen in the Fourier domain. For this, we revisit the model of Harvey (1985) in order to take into account all the components present in the power spectra. This method allows access to two proxies of the activity: the mean spot coverage and the lifetime of the spots. After validating the model with simulated light curves, we present the results from having applied it to thousands of Kepler light curves of main-sequence stars used in McQuillan et al. (2014) and Santos et al. (2022). The results show the emergence of three different regimes of activity related to different levels of spot coverage and long or short spot lifetimes. These regimes are linked to different stellar properties such as their rotation period, mass and Rossby number, which can provide information about the stellar dynamo evolution.