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Observational signatures of infalling envelopes and outflowing material inearly stages of protostellar evolution, and at small radii from the protostar,are essential to progress in the understanding of the mass-accretion process instar formation. In this letter, we report a detailed study of the accretion andoutflow structure around a protostar in the well-known high-mass star-formingregion AFGL 5142. We focus on the mm source MM-1, which exhibits hot-corechemistry, radio continuum emission, and strong water and methanol masers.Remarkably, our Very Long Baseline Interferometry (VLBI) observations ofmolecular masers over six years provided us with the 3-D velocity field ofcircumstellar molecular gas with a resolution of 0.001-0.005 arcseconds and atradii <0.23 arcseconds (or 400 AU) from the protostar. In particular, ourmeasurements of methanol maser emission enabled, for the first time, a directmeasurement of infall of a molecular envelope (radius of 300 AU and velocity of5 km/s) onto an intermediate- to high-mass protostar. We estimate an infallrate of 0.0006 n_8 Msun/year, where n_8 is the ambient volume density in unitsof 10^8 cm-3 (required for maser excitation). In addition, our measurements ofwater maser (and radio continuum) emission identify a collimated bipolarmolecular outflow (and ionized jet) from MM-1. The evidence of simultaneousaccretion and outflow at small spatial scales, makes AFGL 5142 an extremelycompelling target for high-angular resolution studies of high-mass starformation.

Infall and outflow within 400 AU from a high-mass protostar. 3-D velocity fields from methanol and water masers in AFLG 5142