Older Ages for 23 Pre-Main Sequence Stars in Upper Scorpius Using Dynamical Mass-Constrained Stellar Evolutionary Models

TL;DR

This study revises the ages of 23 pre-main sequence stars in Upper Scorpius using dynamical mass constraints, finding that magnetic models yield ages consistent with the region's older age estimate, impacting our understanding of stellar evolution and disk lifetimes.

Contribution

It introduces a method of applying dynamical mass constraints to stellar evolutionary models, improving age estimates for young stars and highlighting the importance of magnetic effects in models.

Findings

Magnetic models produce ages of 9-10 Myr consistent with literature.

Mass constraints increase stellar ages and reduce model scatter.

Standard models without magnetic effects yield younger ages.

Abstract

We present revised stellar ages for 23 pre-main sequence K- and M-type stars in the Upper Scorpius star-forming region, derived by using stellar dynamical masses to constrain isochronal ages from five pre-main sequence stellar evolutionary models. We find that mass-constrained stellar ages for all model sets are more consistent with the older, ~8-11 Myr age for Upper Sco derived using earlier-type stars. Additionally, applying the independent mass constraint to isochronal ages tends to 1) increase stellar ages for most model sets, and 2) decrease age scatter for individual sources between model sets. Models that account for global magnetic fields consistently produce the best match to our observations: they change comparatively little when the mass constraint is applied, and produce 9-10 Myr ages under both unconstrained and mass-constrained conditions. Most standard (nonmagnetic) models produce younger ages (3-5 Myr) when unconstrained, but older ages (6-9 Myr) when constrained by dynamical mass. Our results are consistent with literature findings that suggest median disk lifetimes may be >2x longer than previously thought.