Extending the Asteroseismic Calibration of the Stellar Rossby Number

TL;DR

This paper refines the calibration of the stellar Rossby number using an expanded asteroseismic sample and Gaia data, extending its applicability to redder stars and improving understanding of stellar magnetic activity.

Contribution

It provides an extended and more accurate calibration of the Rossby number across a broader range of stellar types using combined asteroseismic and activity data.

Findings

Quadratic fit to the combined sample is nearly linear between 0.55 < G_BP-G_RP < 1.2.

Calibration extends to spectral types F5 to K3.

Deviation from linearity may be due to observational biases at higher activity levels.

Abstract

The stellar Rossby number (Ro) is a dimensionless quantity that is used in the description of fluid flows. It characterizes the relative importance of Coriolis forces on convective motions, which is central to understanding magnetic stellar evolution. Here we present an expanded sample of Kepler asteroseismic targets to help calibrate the relation between Ro and Gaia color, and we extend the relation to redder colors using observations of the mean activity levels and rotation periods for a sample of brighter stars from the Mount Wilson survey. Our quadratic fit to the combined sample is nearly linear between 0.55 < G_BP-G_RP < 1.2, and can be used to estimate Ro for stars with spectral types between F5 and K3. The strong deviation from linearity in the original calibration may reflect an observational bias against the detection of solar-like oscillations at higher activity levels for the coolest stars.