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M.R. Hogerheijde (Astronomy Department, UC Berkeley)
This paper presents the identification of a transitional stage in the formation of a low-mass star, intermediate between the fully embedded and the T Tauri phases. Millimeter-interferometer molecular-line observations trace the distinctly different velocity fields around two embedded young stellar objects: TMC 1 (IRAS 04381+2517) and L1489 IRS (IRAS 04016+2610). The former is well described by inside-out collapse of a slowly rotating core, while the latter is surrounded by a 2000 AU radius, flared disk in Keplerian rotation around a 0.65 M\sun star. Inward motions in this disk indicate that it will contract to the few hundred AU size scale typical of T Tauri disks on the relatively short time scale of 20,000 yr, or 5% of the embedded stage. These observations suggest that circumstellar disks grow from collapsing, slowly rotating envelopes to a maximum size of a few thousand AU and subsequently contract to several hundred AU prior to the T Tauri phase. It follows that the transfer and dissipation of angular momentum may crucially determine the mass and size of disks around young stars and the conditions of planetary system formation.
The research of M.R.H. is supported by the Miller Institute for Basic Research in Science.