Near-infrared spectroscopic observations of young stellar objects

We present medium-resolution observations of the Br γ and Br α emission lines for 20 pre-main-sequence stars, most of which are low-luminosity objects. In 10 of these, strong Br γ emission has been detected, whose intensity exceeds that expected from the value in Case B recombination with Lyman continuum radiation from the stars. The line ratio (Br α/Br γ) suggests that these lines are emitted from optically thick regions. For low-luminosity stars these lines are considered to come from neutral and dense circumstellar regions. We discuss some existing models of emission mechanism and present a simple calculation to explain our results. (author)