Using rotation, magnetic activity and lithium to estimate the ages of low mass stars

TL;DR

This paper reviews how rotation, magnetic activity, and lithium levels serve as empirical indicators for estimating the ages of low-mass stars, discussing their physics, measurement precision, limitations, and the robust lithium depletion boundary method.

Contribution

It provides a comprehensive review of empirical age indicators for low-mass stars, analyzing their physics, measurement accuracy, limitations, and highlighting the lithium depletion boundary as a robust age estimator.

Findings

Empirical indicators vary in precision and applicability.

Lithium depletion boundary offers nearly model-independent ages.

Limitations depend on star mass and age range.

Abstract

The rotation rate, level of magnetic activity and surface lithium abundance are age-dependent quantities in stars of about a solar mass and below. The physical reasons for the evolution of these phenomena are qualitatively understood, but accurate quantitative models remain dependent on empirical calibration using the Sun and stars of known age, chiefly in clusters. In this work I review the status of these "empirical age indicators", outlining the astrophysics of their time dependence, describing the measurements, assessing the precision (and accuracy) of age estimates when applied to individual stars, and identifying their principle limitations in terms of the mass and age ranges over which they are useful. Finally, I discuss the "lithium depletion boundary" technique which, in contrast to the empirical methods, appears to provide robust, almost model-independent ages that are both precise and accurate, but which is only applicable to coeval groups of stars.