Age spreads in star forming regions?

TL;DR

This paper introduces a method using stellar rotation data to estimate age spreads in star forming regions, revealing significant age dispersions that challenge the assumption of coevality in young clusters.

Contribution

It demonstrates a novel technique combining rotation periods and velocities to infer age spreads, providing more reliable age estimates than traditional methods.

Findings

Radius spreads of a factor of 2-3 at given temperatures in the ONC

Age dispersions larger than the mean cluster age

Implications for PMS evolution studies

Abstract

Rotation periods and projected equatorial velocities of pre-main-sequence (PMS) stars in star forming regions can be combined to give projected stellar radii. Assuming random axial orientation, a Monte-Carlo model is used to illustrate that distributions of projected stellar radii are very sensitive to ages and age dispersions between 1 and 10 Myr which, unlike age estimates from conventional Hertzsprung-Russell diagrams, are relatively immune to uncertainties due to extinction, variability, distance etc. Application of the technique to the Orion Nebula cluster reveals radius spreads of a factor of 2--3 (FWHM) at a given effective temperature. Modelling this dispersion as an age spread suggests that PMS stars in the ONC have an age range larger than the mean cluster age, that could be reasonably described by the age distribution deduced from the Hertzsprung-Russell diagram. These radius/age spreads are certainly large enough to invalidate the assumption of coevality when considering the evolution of PMS properties (rotation, disks etc.) from one young cluster to another.