Dynamical masses of young stellar objects with the VLBA: DYNAMO-VLBA: Radio binary stars in Orion

TL;DR

This study uses VLBA radio observations to measure the masses of young stellar objects in Orion, confirming models and revealing new insights into stellar magnetism and unseen companions.

Contribution

First multi-epoch VLBA survey providing model-independent stellar masses for young binaries in Orion, including intermediate-mass stars and unseen companions.

Findings

Keplerian orbits yield model-independent stellar masses.

VLBA confirms NU Ori C as an intermediate-mass star with magnetic activity.

Astrometric accelerations reveal unseen companions.

Abstract

We present results from a multi-epoch Very Long Baseline Array (VLBA) survey conducted as part of the DYNAMO-VLBA project, aimed at measuring the dynamical masses of young stellar systems in the Orion complex. Our observations include 19 radio sources associated with 15 binary or multiple young systems. For four visual binaries in which both components were detected, the derived Keplerian orbits yield model-independent stellar masses; in particular, Brun~656 and HD~294300 show excellent agreement between VLBA-based and spectral-energy-distribution-based estimates, providing valuable benchmarks for pre-main-sequence evolutionary models. The component NU Ori C is confirmed as an intermediate-mass ($\sim$7\,M$_\odot$) star with nonthermal radio emission, offering rare evidence of magnetic activity near the boundary with the high-mass regime. Several additional sources exhibit astrometric accelerations or periodic residuals, revealing unseen companions and extending dynamical constraints to systems with only one radio-emitting component. These results highlight the capability of very long baseline interferometry astrometry to obtain precise and model-independent masses of young binaries, providing critical empirical anchors for stellar evolution models and new insights into the origin of magnetism in intermediate-mass stars.