Mid-infrared interferometry on spectral lines. III. Ammonia and silane around IRC+10216 and VY canis majoris

Using the University of California Berkeley Infrared Spatial Interferometer with a radio frequency (RF) filter bank, the first interferometric observa tions of mid-infrared molecular absorption features of ammonia (NH3) and si lane (SiH4) with very high spectral resolution (lambda/Delta lambda similar to 10(5)) were made. Under the assumptions of spherical symmetry and unifo rm outflow, these new data permitted the molecular stratification around ca rbon star IRC +10216 and red supergiant VY CMa to be investigated. For IRC + 10216, both ammonia and silane were found to form in the dusty outflow si gnificantly beyond both the dust formation and gas acceleration zones. Spec ifically, ammonia was found to form before silane in a region of decaying g as turbulence (greater than or equal to 20R(*)), while the silane is produc ed in a region of relatively smooth gas flow much farther from the star (gr eater than or similar to 80R(*)). The depletion of gas-phase SiS onto grain s soon after dust formation may fuel silane-producing reactions on the grai n surfaces. For VY CMa, a combination of interferometric and spectral obser vations suggest that NH3, is forming near the termination of the gas accele ration phase in a region of high gas turbulence (similar to 40R(*)).