Wide binaries stars as probes of the magnetic activity enhancement during the spin-down stalling phase

Résumé fourni par la source

Stellar magnetic activity is generated by the interplay of rotation and convection. As they age, solar-like stars spin down and become less active. This was thought to be a monotonic behavior, but the Kepler mission revealed a phase of stalled spin down, during which the rotation period remains nearly constant, while magnetic activity is enhanced. The transition associated to this stalling manifests as an underdensity in the rotation-temperature distribution, commonly referred to as the intermediate rotation gap. In this work, we investigate the signature of spin-down stalling in the magnetic activity of wide binaries. Wide binary components undergo independent evolution, as their large separations ($\gtrsim 10^{3}$ au) ensure negligible interactions, preserving the magnetic and rotational evolution of single stars. Comparing coeval stars on either side of the transition allows us to study changes in magnetic activity, independently of age and composition. We analyze a sample of 372 wide binaries, identified in the literature via Gaia astrometry and observed by NASA Kepler and K2 missions, for which we recover rotation periods and magnetic activity indexes ($S_\text{ph}$). A calibration of the convective turnover time is performed on seismic stars based on their corrected Gaia colors. This allows us to calculate the Rossby number, defined as the ratio of the rotation period to the convective turnover time. We compare their rotation-activity-color distributions to those of the full Kepler field population. We show that the wide binary distribution in the activity-rotation diagram closely mirrors the full Kepler main-sequence field population, with the upper envelope reproducing the gap and an enhanced magnetic activity at the transition. To further probe this, we examine individual pairs straddling the gap and find evidence that post-transition stars can exhibit higher magnetic activity than the pre-transition star, supporting a change in magnetic activity regime. The upcoming PLATO mission will provide the opportunity to extend this analysis to a larger population of wide binaries observed within its fields. This study will help better understand stellar evolution, as well as the environment around stars and the impact on the habitability of their orbiting exoplanets.

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