On the origin of the HI line emission associated with massive young stellar objects
The problem of interpreting the H I line emission associated with massive young stellar objects is addressed by comparing results of LTE calculations of H I Br-alpha and Pf-gamma profiles with observations of the exciting source of Sh2-106 obtained by Garden and Geballe (1986). The theoretical results are derived by a formal solution of the transfer equation as applied to a spherically symmetric stellar wind. Free-free and bound-free opacity is taken into account. The effects of departures from LTE upon the line fluxes and flux ratio are discussed, and it is proposed that the observed asymmetry in the Pf-gamma profile is due to the combined effect of free-free opacity and a line source function that exceeds its LTE value.