Are the gyro-ages of field stars underestimated?

TL;DR

This study reveals that current gyro-age estimates for field stars are systematically underestimated compared to isochrone ages, indicating that stellar rotation slows down more slowly than previously thought, challenging existing gyrochronology models.

Contribution

The paper introduces a simple additive gyro-age calibration and demonstrates its effectiveness across multiple datasets, highlighting limitations of traditional gyrochronology methods.

Findings

Gyro-ages are generally greater than isochrone ages for field stars.

Systematic differences can exceed several billion years.

Current gyrochronology models may underestimate stellar ages.

Abstract

By using the current photometric rotational data on eight galactic open clusters, we show that the evolutionary stellar model (isochrone) ages of these clusters are tightly correlated with the period shifts applied to the (B-V)_0 - P_rot ridges that optimally align these ridges to the one defined by Praesepe and the Hyades. On the other hand, when the traditional Skumanich-type multiplicative transformation is used, the ridges become far less aligned due to the age-dependent slope change introduced by the period multiplication. Therefore, we employ our simple additive gyro-age calibration on various datasets of Galactic field stars to test its applicability. We show that, in the overall sense, the gyro-ages are systematically greater than the isochrone ages. The difference could exceed several giga years, depending on the stellar parameters. Although the age overlap between the open clusters used in the calibration and the field star samples is only partial, the systematic difference indicates the limitation of the currently available gyro-age methods and suggests that the rotation of field stars slows down with a considerably lower speed than we would expect from the simple extrapolation of the stellar rotation rates in open clusters.