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

TL;DR

This study investigates the kinematics of discs and winds around intermediate and high-mass young stellar objects, revealing dense environments, disc presence, and ionized outflows, with implications for star formation processes.

Contribution

First demonstration that broad line wings are due to Stark broadening, and fitting of Keplerian disc models to fluorescent FeII lines in massive YSOs.

Findings

Broad line wings caused by Stark broadening or electron scattering.

Evidence for dense circumstellar environments and disc-wind structures.

FeII line fits support the presence of Keplerian discs.

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.