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Session 20 - Chemistry & Physical Process in the ISM.
Display session, Wednesday, January 07
There is growing evidence of a connection between H_2O masers clustered around newly formed stars and supersonic turbulence generated in the interface between outflows from these stars and surrounding quiescent gas. Studying this connection is important in understanding both supersonic turbulence and the nature of H_2O masers themselves. The purpose of the present study was to investigate, in more detail than done before, indications of turbulence in W49N, the strongest galactic H_2O maser source. I studied the statistical properties of the spatial distribution and velocity field of H_2O masers in W49N in order to compare them to statistical properties characteristic of turbulence. Using the published VLBI radial velocities and spatial coordinates of the maser spots, I calculated velocity structure functions of different order, as well as the density-radius fractal measure for the spatial distribution of the maser spots. I find that the statistical parameters of the velocity field have a strong tendency toward their classical (Kolmogorov) values for the source as a whole, for a subset of central maser spots, and for a subset of low velocity maser spots. These regions also demonstrate a good power law dependence of the average number density of the maser spots on a scale, with an ensuing low fractal dimension, d \sim 0.5. The Kolmogorov-type velocity spectrum and the fractal geometrical structure are both strong indications of turbulence. I confirm, thereby, the hypothesis that H_2O masers are connected to supersonic turbulence.
Program listing for Wednesday