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N. H. Volgenau (U. Maryland)
Standard star formation theory asserts that dense protostellar cores originate as quiescent inhomogeneities in molecular clouds and evolve in relative isolation. Observations of dense cores, however, reveal the incompleteness of the theory: protostars tend to form in proximity to each other, often as binary or multiple systems, and drive powerful molecular outflows that disturb their environments.
Turbulence, which is inferred on large scales from molecular line widths, has long been suggested as an essential ingredient of the star formation process. Recent theoretical works (e.g. Padoan et al. 2001, Burkert & Bodenheimer 2000) posit that dense cores are dynamic rather than quiescent phenomena. The cores form rapidly at collision interfaces of turbulent flows and evolve according to the local conditions (density, velocity field, magnetic field). The tenability of this theory is gaining observational support (cf. Caselli et al. 2002).
We investigate the hypothesis that turbulence persists down to scales of thousands or hundreds of AU by analyzing the velocity fields in the envelopes of dense cores. Our investigation has three primary strengths: 1. a large sample of cores, 2. maps created from multiple optically thin lines, and 3. coverage over a wide range of spatial frequencies. The cores presented are all targets from the BIMA survey of the Perseus Cloud Complex (Volgenau et al. 2002). Observations were made with three configurations of the BIMA array, as well as the FCRAO 14-meter telescope, allowing the cores to be mapped with resolutions from ~50 arc-seconds down to 3 arc-seconds. The latter resolution corresponds to approximately 1000AU at the distance of Perseus. We find that the velocity fields are complex and not easily explained by simple kinematic models (e.g. uniform rotation). Further, thermal broadening at temperatures representative of the bulk of the core envelopes is insufficient to explain the widths of the molecular lines. We analyze the velocity fields using a technique suggested by Ostriker, Stone, and Gammie (2001) that does not require the determination of model-specific phenomena, such as a fulcrum for a velocity gradient. We find that the velocity dispersions of the lines show considerable scatter when evaluated over small beamsizes, a result that is consistent with models of turbulent clouds.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.