Journal Article

The circumstellar disc, envelope and bipolar outflow of the massive young stellar object W33A

Ben Davies, Stuart L. Lumsden, Melvin G. Hoare, René D. Oudmaijer and Willem-Jan de Wit

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 3, pages 1504-1515
Published in print March 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI:
The circumstellar disc, envelope and bipolar outflow of the massive young stellar object W33A

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The young stellar object (YSO) W33A is one of the best known examples of a massive star still in the process of forming. Here we present Gemini North Altitude conjugate Adaptive optics for the Infrared (ALTAIR)/Near-Infrared Integral Field Spectrograph laser-guide star adaptive-optics assisted K-band integral-field spectroscopy of W33A and its inner reflection nebula. In our data, we make the first detections of a rotationally flattened outer envelope and fast bipolar jet of a massive YSO at near-infrared wavelengths. The predominant spectral features observed are Br γ, H2 and a combination of emission and absorption from CO gas. We perform a 3D spectro-astrometric analysis of the line emission, the first study of its kind. We find that the object's Br γ emission reveals evidence for a fast bipolar jet on sub-milliarcsecond scales, which is aligned with the larger scale outflow. The hybrid CO features can be explained as a combination of hot CO emission arising in a disc close to the central star, while cold CO absorption originates in the cooler outer envelope. Kinematic analysis of these features reveals that both structures are rotating and consistent with being aligned perpendicular to both the ionized jet and the large-scale outflow. Assuming Keplerian rotation, we find that the circumstellar disc orbits a central mass of ≳10 M, while the outer envelope encloses a mass of ∼15 M. Our results suggest a scenario of a central star accreting material from a circumstellar disc at the centre of a cool extended rotating torus, while driving a fast bipolar wind. These results therefore provide strong supporting evidence for the hypothesis that the formation mechanism for high-mass stars is qualitatively similar to that of low-mass stars.

Keywords: stars: pre-main-sequence; ISM: individual: W33a; ISM: H ii regions

Journal Article.  7204 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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