Evidence for residual material in accretion disk gaps: CO fundamental emission from the T Tauri spectroscopic binary DQ Tauri

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 nu = 1 and nu = 2 vibrational levels with line widths of roughly 70 km s(-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 5 x 10(-4) g cm(-2) that extends outward to 0.5 +/- 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 Tau's spectral energy distribution, as evidence for a small amount (similar to 10(-10) M.) 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.