Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

We report on the detection and analysis of hot ro-vibrational H2O emission from SVS-13, a young stellar object previously known to have strong CO overtone bandhead emission. Modeling of the high-resolution infrared spectrum shows that the H2O emission is characterized by temperatures ~ 1500 K, significantly lower than the temperatures that characterize the CO bandhead emission. The widths for the H2O lines are also found to be smaller than those for the CO lines. We construct a disk model for the emission that reproduces the CO and H2O spectrum. In this model, the H2O lines originate at somewhat larger disk radii (<= 0.3 AU) than the CO overtone lines (<= 0.1 AU). We find that the H2O 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 bandhead. 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.