Molecular Gas in the Inner 1 AU of the TW Hya and GM Aur Transitional Disks

Abstract

We report the detection of CO rovibrational emission from the transitional disks around the T Tauri stars TW Hya and GM Aur. Transitional disks are characterized by significant mid- to far-infrared (IR) dust emission combined with a relative deficit in the near-IR, indicating the presence of an optically thick outer disk but a reduced surface density of small dust grains in the inner disk. Kinematic fits to the resolved CO emission lines demonstrate that they arise from within the tenuous inner disk. Excitation diagram analyses yield rotational temperatures also consistent with small emission radii as well as densities implying dynamically significant amounts of gas in the inner disk and a gas-to-small dust grain ratio in excess of that in dense clouds. Nevertheless, gas densities are not high enough to maintain current accretion rates for more than a few hundred years without replenishment, and transfer of gas from the outer to inner disk is therefore likely required.