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 emissionfrom SVS-13, a young stellar object previously known to have strong CO overtonebandhead emission. Modeling of the high-resolution infrared spectrum shows thatthe H2O emission is characterized by temperatures ~ 1500 K, significantly lowerthan the temperatures that characterize the CO bandhead emission. The widthsfor the H2O lines are also found to be smaller than those for the CO lines. Weconstruct a disk model for the emission that reproduces the CO and H2Ospectrum. 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 H2Oabundance is about a factor of 10 lower than the calculated chemicalequilibrium abundance. Large, approximately transonic, local line broadening isrequired to fit the profile of the CO bandhead. If this velocity dispersion isidentified with turbulence, it is of significant interest regarding thetransport of angular momentum in disks. Large local broadening is also requiredin modeling CO overtone emission from other young stellar objects, suggestingthat large turbulent velocities may be characteristic of the upper atmospheresof the inner disks of young stars.Comment: 26 pages, 7 figures to be published in The Astrophysical Journa