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Session 20 - Molecular Clouds, Dense Cores, and Protostars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[20.08] Non-LTE Effects in Ammonia

R. A. Gaume, T. L. Wilson, K. J. Johnston (USNO, MPIfR, USNO)

The non-LTE effects in the NH_3 (J,K)=(1,1) absorption toward the DR 21 HII region have been investigated using a spatial resolution of 3 arcseconds. The anomalies, found in the satellite hyperfine (HF) components, indicate significant, widespread departures from LTE. We present images of the LTE departure for the inner and outer pairs of NH_3 (1,1) HF components toward the HII region, and find surprisingly, that the degree of LTE departure for these HF components is spatially anticorrelated. Previous models predicted a spatial correlation. This unexpected result may be explained by a dynamic model involving both the infall and outflow of molecular material. Although weak emission in the redshifted outer HF component is widespread toward the continuum, an unresolved, high brightness temperature (greater than 600K) maser is found just SW of the continuum peak. This is the first proven instance of an interstellar maser in the NH_3 (1,1) level. The flux density of the maser is larger than the absolute value of the flux density of any of the other HF components (seen in absorption), including the main component.

Program listing for Monday