CIRCUMBINARY GAS ACCRETION ONTO A CENTRAL BINARY: INFRARED MOLECULAR HYDROGEN EMISSION FROM GG Tau A

We present high spatial resolution maps of ro-vibrational molecular hydrogen emission from the environment of the GG Tau A binary component in the GG Tau quadruple system. The H-2 nu = 1-0 S(1) emission is spatially resolved and encompasses the inner binary, with emission detected at locations that should be dynamically cleared on several hundred year timescales. Extensions of H-2 gas emission are seen to similar to 100 AU distances from the central stars. The nu = 2-1 S(1) emission at 2.24 mu m is also detected at similar to 30 AU from the central stars, with a line ratio of 0.05 +/- 0.01 with respect to the nu = 1-0 S(1) emission. Assuming gas in LTE, this ratio corresponds to an emission environment at similar to 1700 K. We estimate that this temperature is too high for quiescent gas heated by X-ray or UV emission from the central stars. Surprisingly, we find that the brightest region of H-2 emission arises from a spatial location that is exactly coincident with a recently revealed dust "streamer" which seems to be transferring material from the outer circumbinary ring around GG Tau A into the inner region. As a result, we identify a new excitation mechanism for ro-vibrational H-2 stimulation in the environment of young stars. The H-2 in the GG Tau A system appears to be stimulated by mass accretion infall as material in the circumbinary ring accretes onto the system to replenish the inner circumstellar disks. We postulate that H-2 stimulated by accretion infall could be present in other systems, particularly binaries and "transition disk" systems which have dust-cleared gaps in their circumstellar environments.