Two-dimensional Monte Carlo simulations of H I line formation in massive young stellar object disc winds

Abstract

Massive young stellar objects (YSOs) are powerful infrared H I line emitters. It has been suggested that these lines form in a outflow from a disk surrou nding the YSO. Here, new two-dimensional Monte Carlo radiative transfer calculations are described which test this hypothesis. Infrared spectra are synthesised for a YSO disk wind model based on earlier hydrodynamical calculations. The model spectra are in qualitative agreement with the observed spectra from massive YSOs, and therefore provide support for a disk wind explanation for the H I lines. However, there are some significant differences: the models tend to overpredict the Brα/Brγ ratio of equivalent-widths and produce line profiles which a re slightly too broad and, in contrast to typical observations, are double-peake d. The interpretation of these differences within the context of the disk wind picture and suggestions for their resolution via modifications to the assumed disk and outflow structure are di scussed.