Accretion onto Pre-Main Sequence Binary Stars: The Circumstellar Environment

Observations show that mass accretion can occur at the surfaces of stars in young binaries of all separations. Given that resonant torques have been expected to clear gaps and dam the inward flow of material from circumbinary disks, this result begs the question of how mass accretion is supplied in binary systems. In this paper we address this question in the context of close binaries. Spectral energy distributions indicate that dynamical clearing is not complete for close binaries having massive circumbinary disks. High-resolution infrared spectra of CO rotational and ro-vibrational lines have also detected small amounts of gas which can be located in the region of dynamical clearing. Thus we have signatures of matter from the circumbinary environment through the predicted gap region to the stellar surfaces. We suggest that accretion streams may supply both dynamically cleared regions and circumstellar disks.