Hot H 2 O Emission and Evidence for Turbulence in the Disk of a Young Star

We report on the detection and analysis of hot rovibrational H 2 O emission from SVS 13, a young stellar object previously known to have strong CO overtone band head emission. Modeling of the high-resolution infrared spectrum shows that the H 2 O emission is characterized by temperatures of ~1500 K, significantly lower than the temperatures that characterize the CO band head emission. The widths of the H 2 O lines are also found to be smaller than those of the CO lines. We construct a disk model of the emission that reproduces the CO and H 2 O spectrum. In this model, the H 2 O lines originate at somewhat larger disk radii (≤0.3 AU) than the CO overtone lines (≤0.1 AU). We find that the H 2 O abundance is about a factor of 10 lower than the calculated chemical equilibrium abundance. Large, approximately transonic, local line broadening is required to fit the profile of the CO band head. If this velocity dispersion is identified with turbulence, it is of significant interest regarding the transport of angular momentum in disks. Large local broadening is also required in modeling CO overtone emission from other young stellar objects, suggesting that large turbulent velocities may be characteristic of the upper atmospheres of the inner disks of young stars.