From Infall to Rotation Around Young Stellar Objects

We present evidence of a short-lived, transitional stage between the fully embedded and optically visible stages of low-mass star formation. This stage is characterized by a large (2000 AU radius) disk with close-to Keplerian motions, but with a significant inward component to the velocity field. Millimeter-interferometric observations of HCO^+ J=1-0 and 3-2 first identified this structure around the embedded object L1489 IRS, with inward motions present on scales of several hundred AU. Subsequent R≈25,000 M-band spectroscopy showed that the inward motions extend to within 0.1 AU from the star. We conclude that angular-momentum transfer is crucial in determining the final density distribution in the disk and the initial conditions for planet formation.