Masses and Implications for Ages of Low-Mass Pre-Main Sequence Stars in Taurus and Ophiuchus

TL;DR

This study compares dynamical masses of low-mass pre-main sequence stars in Taurus and Ophiuchus with theoretical models, finding magnetic field-inclusive models yield more accurate mass and age estimates, supporting older stellar ages.

Contribution

It provides new dynamical mass measurements and demonstrates that magnetic field effects are essential for accurate mass and age determination of PMS stars.

Findings

Magnetic models improve mass estimates accuracy.

Stars are older (3-10 Myr) than non-magnetic models suggest.

Dynamical masses agree with magnetic field-inclusive models.

Abstract

The accuracy of masses of pre-main sequence (PMS) stars derived from their locations on the Hertzsprung-Russell Diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least $10 \%$. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M$_{dyn}$, is drawn from a larger list of 39 targets in the Taurus SFR and 6 in the Ophiuchus SFR. Placing the stars with accurate and precise dynamical masses on HRDs that do not include internal magnetic fields underestimates the mass compared to M$_{dyn}$ by about $30 \%$. Placing them on an HRD that does include magnetic fields yields mass estimates in much better agreement with M$_{dyn}$, with an average difference between M$_{dyn}$ and the estimated track mass of $0.01\pm0.02$~\msun. The ages of the stars, 3--10 MY on tracks that include magnetic fields, is older than the 1--3 MY indicated by the non-magnetic models. The older ages of T Tauri stars predicted by the magnetic models increase the time available for evolution of their disks and formation of the giant gas exoplanets. The agreement between our M$_{dyn}$ values and the masses on the magnetic field tracks provides indirect support for these older ages.