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B.A. Biller (Swarthmore College and Maria Mitchell Observatory), V.S. Strelnitski (Maria Mitchell Observatory)
The 1.35-cm H2O masers in sites of star formation typically display very narrow line widths, narrower than the separation of the three strongest hyperfine components of the transition, as well as unexpectedly steep variation in linewidth as a function of intensity. We critically analyze various mechanisms proposed to explain these observations. These include narrowing due to unsaturated amplification in various geometries and blending of two features. The linewidths of a number of maser features remain unexplained by any of these or other proposed mechanisms. In particular, unsaturated amplification can produce the observed narrow line widths but it is insufficient to produce the observed steepness of line narrowing with increasing intensity. Blending can provide the necessary rate of line narrowing but it produces characteristic shifts in the central velocity of the line that are not observed in a number of features. We suggest that an as yet unknown nonlinear effect of frequency mode competition may be responsible for both the narrowness and the high rate of narrowing of these lines. This project was supported by the NSF/REU grant AST-9820555.
The author(s) of this abstract have provided an email address for comments about the abstract: beth@sccs.swarthmore.edu