Tracers of Discs and Winds around Intermediate and High Mass Young Stellar Objects

Abstract

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 ($\sim500$kms$^{-1}$) symmetric line wings on the HI 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 disc-wind 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 FeII 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 picture is one in which these stars still have accretion discs, with a very
dense inner circumstellar environment which may be tracing either the inner
regions of a disc, or of a stellar wind, and in which ionised 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.