Joan Rie Najita

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

Abstract : We report on the detection and analysis of hot rovibrational H2O 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 H2O emission is characterized by temperatures of 1500 K, significantly lower than the temperatures that characterize the CO band head emission. The widths of the H2O 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 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 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.

Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri

Abstract : We present the discovery of CO fundamental rovibrational emission from the classical T Tauri spectroscopic binary DQ Tau. The high-resolution infrared echelle spectra reveal emission lines from both the gamma = 1 and gamma = 2 vibrational levels with line widths of roughly 70 km s(exp -1). The average CO excitation temperature is approximately 1200 K. We model the spectra as arising from gas in Keplerian rotation about the center of mass of the binary. The disk model requires gas with an average surface density of 5x10(exp -4) g sq cm that extends outward to 0.5 plus or minus 0.1 AU and inward to at least 0.1 AU from the center of mass. The radial extent for the emitting gas is close to the predicted size of the gap in the DQ Tau accretion disk that is expected to be dynamically cleared by the binary. We interpret these results, and previous modeling of DQ TauSs spectral energy distribution, as evidence for a small amount (~10(exp 10) M circle dot solar of diffuse material residing within the optically thin disk gap. Thus, dynamical clearing has not been completely efficient in the DQ Tau binary. We suggest that the material is associated with a flow from the circumbinary disk which feeds the ongoing accretion at the stellar surfaces.