Tracers of discs and winds around intermediate- and high-mass young stellar objects
Lumsden, S. L.
We present a study of the kinematical properties of a small sample of nearby near-infrared bright massive and intermediate-mass young stellar objects using emission lines sensitive to discs and winds. We show for the first time that the broad (similar to 500 km s-1) symmetric line wings on the H i Brackett series lines are due to Stark broadening or electron scattering, rather than pure Doppler broadening due to high-speed motion. The results are consistent with the presence of a very dense circumstellar environment. In addition, many of these lines show evidence for weak line self-absorption, suggestive of a wind or discwind origin for that part of the absorbing material. The weakness of the self-absorption suggests a large opening angle for such an outflow. We also study the fluorescent 1.688 mu m Fe ii line, which is sensitive to dense material. We fitted a Keplerian disc model to this line, and find reasonable fits in all bar one case, in agreement with previous finding for classical Be stars that fluorescent iron transitions are reasonable disc tracers. Overall, the evidence suggests these stars still have accretion discs, with a very dense ionized inner circumstellar environment which may be tracing either the inner regions of the disc or of a stellar wind, and in which ionized outflow is also present. The similarity with lower mass stars is striking, suggesting that at least in this mass range they form in a similar fashion.