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 ro-vibrational emission from theclassical T Tauri spectroscopic binary DQ Tau. The high-resolution infraredechelle spectra reveal emission lines from both the v=1 and v=2 vibrationallevels with line widths of roughly 70 km/s. The average CO excitationtemperature is approximately 1200 K. We model the spectra as arising from gasin Keplerian rotation about the center-of-mass of the binary. The disk modelrequires gas with an average surface density of 5 x 10-4 g cm-2 that extendsoutward to 0.5 +/- 0.1 AU and inward to at least 0.1 AU from thecenter-of-mass. The radial extent for the emitting gas is close to thepredicted size of the gap in the DQ Tau accretion disk that is expected to bedynamically cleared by the binary. We interpret these results, and previousmodeling of DQ Tau's spectral energy distribution, as evidence for a smallamount (~ 1e-10 Msun) of diffuse material residing within the optically-thindisk gap. Thus dynamical clearing has not been completely efficient in the DQTau binary. We suggest that the material is associated with a flow from thecircumbinary disk which feeds the ongoing accretion at the stellar surfaces.Comment: to be published in The Astrophysical Journa