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) Ðlter bank, the Ðrst interferometric observations of mid-infrared molecular absorption features of ammonia and silane with very high spectral resolution (j/*jD 105) were made. Under the 3 4 assumptions of spherical symmetry and uniform outÑow, these new data permitted the molecular stratiÐcation around carbon 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 outÑow signiÐcantly beyond both the dust formation and gas acceleration zones. SpeciÐcally, ammonia was found to form before silane in a region of decaying gas turbulence while the silane is produced in a region of relatively (Z20R * ), smooth gas Ñow much farther from the star The depletion of gas-phase SiS onto grains soon (Z80R * ). after dust formation may fuel silane-producing reactions on the grain surfaces. For VY CMa, a combination of interferometric and spectral observations suggest that is forming near the termination 3 of the gas acceleration phase in a region of high gas turbulence (D40R * ). Subject headings : circumstellar matter È instrumentation : interferometers È instrumentation : spectrographs È molecular processes È stars : AGB and post-AGB È turbulence