Probing discs around massive young stellar objects with CO first overtone emission

TL;DR

This study uses high-resolution spectroastrometry of CO overtone emission to investigate the presence of circumstellar disks around massive young stellar objects, supporting the theory of disk-mediated star formation.

Contribution

First detailed spectroastrometric analysis of CO overtone emission in massive young stars, confirming the disk origin of the emission and supporting the disk accretion model for massive star formation.

Findings

CO bandhead emission likely originates from small-scale disks

No direct spatial signatures of disks detected at high angular resolution

Results support disk accretion as a formation mechanism for massive stars

Abstract

We present high resolution (R~50,000) spectroastrometry over the CO 1st overtone bandhead of a sample of seven intermediate/massive young stellar objects. These are primarily drawn from the red MSX source (RMS) survey, a systematic search for young massive stars which has returned a large, well selected sample of such objects. The mean luminosity of the sample is approximately 5 times 10^4 L_\odot, indicating the objects typically have a mass of ~15 solar masses. We fit the observed bandhead profiles with a model of a circumstellar disc, and find good agreement between the models and observations for all but one object. We compare the high angular precision (0.2-0.8 mas) spectroastrometric data to the spatial distribution of the emitting material in the best-fitting models. No spatial signatures of discs are detected, which is entirely consistent with the properties of the best-fitting models. Therefore, the observations suggest that the CO bandhead emission of massive young stellar objects originates in small-scale disks, in agreement with previous work. This provides further evidence that massive stars form via disc accretion, as suggested by recent simulations.