A calibration of the Rossby number from asteroseismology

Abstract

Stellar activity and rotation are tightly related in a dynamo process. Our understanding of this mechanism is mainly limited by our capability of inferring the properties of stellar turbulent convection. In particular, the convective turnover time is a key ingredient through the estimation of the stellar Rossby number, which is the ratio of the rotation period and the convective turnover time. In this work we propose a new calibration of the (B − V) color index dependence of the convective turnover time, hence of the stellar Rossby number. Our new calibration is based on the stellar structure properties inferred through the detailed modeling of solar-like pulsators using asteroseismic observables. We show the impact of this calibration in a stellar activity -Rossby number diagram by applying it to a sample of about 40,000 stars observed with Kepler and for which photometric activity proxy S ph and surface rotation periods are available. Additionally, we provide a new calibration of the convective turnover time as function of the (G BP − G RP ) color index for allowing applicability in the ESA Gaia photometric passbands.