Enhanced magnetic activity after the intermediate-rotation period gap, as traced by the chromospheric Ca II IRT, and prospects for the PLATO mission

Résumé fourni par la source

For low-mass stars (M < 1.4 Msun), the connection between stellar rotation and magnetic activity governs stellar spin-down, shapes the environments of their exoplanets, and provides an age-diagnostic via gyrochronology. Recently, unexpected phenomena known as the intermediate rotation period gap and the rotational stalling have been discovered. These are likely due to internal angular momentum redistribution, and mark departures from a smooth spin-down evolution. These rotational features have been shown to cause enhanced magnetic activity on the photosphere, as measured by the photometric index from light curves (Sph). However, evidence of their influence on chromospheric magnetic activity remains scarce. In this contribution, I will present the impact of the intermediate-period gap on chromospheric magnetic activity as traced by the Ca II infrared triplet (IRT) index. We target the stars observed by the Kepler mission, as this is the largest and most reliable sample of field stars with measured rotation periods sensitive to the gap, and calculate the Ca II IRT index using spectroscopic information from the third data release of the Gaia mission (Gaia DR3). The rotation-activity relation reveals that chromospheric magnetic activity is also enhanced after the intermediate-period gap, mirroring its effect on the photospheric index Sph. We test the dependence of this result on spectral type, and find that the signature persists in both K and G dwarfs separately, but is absent in F dwarfs. This work demonstrates that the intermediate-period gap marks a genuine transition in stellar magnetic behavior, not only at the photosphere, but also at the chromosphere. These findings provide important context for the interpretation of activity proxies, exoplanet habitability, and the age-rotation-activity relation. Furthermore, expansions of this work applied to PLATO are underway, with preliminary analyses in the Long-duration Observation Phase at South (LOPS2) field resulting in nearly ~1,000 targets in the P1 sample with chromospheric activity measurements from Gaia and rotation periods derived from TESS light curves. This work will help pave the way for future investigations of stellar rotation and magnetic activity evolution in the context of the PLATO mission.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.