3D velocity fields from methanol and water masers in an intermediate-mass protostar

We report multi-epoch VLBI observations of molecular masers towards the high-mass star forming region AFGL 5142, leading to the determination of the 3D velocity field of circumstellar molecular gas at radii <0.''23 (or 400 AU) from the protostar MM-1. Our observations of CH₃OH maser emission enabled, for the first time, a direct measurement of infall of a molecular envelope on to an intermediate-mass protostar (radius of 300 AU, velocity of 5 km s^-1, and infall rate of 6 × 10^-4 n ₈ M _⊙ yr^-1, where n ₈ is the ambient volume density in units of 10⁸ cm^-3). In addition, our measurements of H₂O maser (and radio continuum) emission revealed a collimated bipolar molecular outflow (and ionized jet) from MM-1. The evidence of simultaneous accretion and outflow at small spatial scales, makes AFGL 5142 an extremely compelling target for high-angular resolution studies of high-mass star formation.