The paradox of high precision asteroseismology: the age of stars depends on when you look at them

Following the success of missions like CoRoT, Kepler, and TESS, asteroseismic modelling is poised to play a key role in upcoming space-based missions such as PLATO, CubeSpec, and Roman. Despite remarkable achievements, the era of high-precision asteroseismology has also revealed significant discrepancies between observed data and theoretical stellar models, leading to non-negligible biases in stellar characterisation. Historically, magnetic activity effects were typically overlooked in asteroseismic modelling of solar-type stars, assuming that these effects could be accounted for in the parametrisation of the so-called ‘surface effects’. However, recent studies have challenged this view, demonstrating that magnetic activity significantly impacts asteroseismic characterisation using both forward (Creevey et al. 2011; Pérez Hernández et al. 2019; Thomas et al. 2021; Bétrisey et al. 2024) and inverse methods (Bétrisey et al. 2025a). In this context, we showed that magnetic activity effects cannot be suppressed with standard methods employed to mitigate surface effects (Bétrisey et al. 2025b). When these methods are applied, most stellar parameters correlate with the activity cycle, introducing systematic uncertainties of 4.7%, 2.9%, and 1.0% for the stellar age, mass, and radius, respectively. These biases are significant given the precision demands of future space-based photometry missions. It therefore becomes essential to enhance our theoretical understanding of these effects and develop a modelling procedure capable of accounting for or efficiently suppressing them. In this context, frequency separation ratios may play a crucial role, as they allow for the disentanglement of surface and magnetic activity effects. These advancements will not only benefit future missions but also enhance the asteroseismic characterisation of the most active Kepler targets.