Letter to the Editor

A calibration of the Rossby number from asteroseismology

¹ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia, 78, 95123 Catania, Italy
e-mail: enrico.corsaro@inaf.it
² Instituto de Astrofísica de Canarias, Santa Cruz de Tenerife, Spain
³ Department of Astrophysics, Universidad de La Laguna, Santa Cruz de Tenerife, Spain
⁴ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 26 May 2021
Accepted: 15 July 2021

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 via a stellar activity-Rossby number diagram by applying it to a sample of about 40 000 stars observed with Kepler and for which the values for the photometric activity proxy S​_ph and surface rotation periods are available. Additionally, we provide a new calibration for the convective turnover time as function of the (G_BP − G_RP) color index for allowing applicability in the ESA Gaia photometric passbands.