Evidence for Hco+ Infall toward T Tauri?

Abstract

High spectral and spatial resolution observations of the HCO+ molecule toward the T Tau binary system obtained with the Owens Valley Millimeter Array reveal a broad emission line profile (V_LSR = 7.2 km/s, width = 2.0 km/s) upon which a narrow, redshifted absorption feature (V_LSR = 8.5 km/s, width +/- 0.5 km/s) is superposed. One possible interpretation of the absorption is that it arises from infall of molecular cloud envelope material onto the immediate circumbinary region, which would imply that large scale dynamic accretion processes are still active well into the optically visible stages of star formation. Provided the mass is deposited at radii sufficiently close to the young stars, estimates of the accretion rates indicate that infall may add enough material to the system to account for the FU~Orionis type flares recently observed in T~Tau in =< 100 yr.