# # Program information file # PROGRAM_ID 2023B051 PROGRAM_TITLE High-resolution IR observations of Mira-type variables at different stellar phases - a thorough look at the dynamics of the inner molecular shell PROGRAM_INV1 Guido W. Fuchs PROGRAM_INV2 Eileen Doering PROGRAM_INV3 David Gobrecht PROGRAM_INV4 Thomas K. Greathouse PROGRAM_INV5 Rohini S. Giles PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG In this project, we aim to further investigate the dynamics of the inner molecular envelope of prototypical pulsating M- and S-type stars, such as chi Cyg, o Cet, R Cas, and IK Tau. Mira-type AGB stars show remarkable mass loss leading to the formation of a molecular layer and a dusty envelope around the central star. Molecules such as SiO, TiO, and other species of refractory materials are formed. Pulsation of the stellar photosphere affects the surrounding molecular layer in various ways, such as varying radiation intensity and periodic shocks. Molecules such as SiO and TiO are ideal probes to study the dynamic behavior of the molecular layer and to determine the physical causes of these changes. Our previous high-resolution IR observations have revealed many facets of molecular shell pulsation that have not been observed before. For example, in addition to the strong dependence of 28SiO abundance on stellar phase, an unusually high 29SiO abundance during certain phases of Chi Cyg and the apparent absence of 29SiO at certain times have been observed for the first time. The claim of older publications that Chi Cyg has the same Si isotope ratios as our solar environment must therefore be critically discussed and placed in the context of stellar phase. During recent observing runs, we found something interesting. We have been able to identify a particular stellar phase where the SiO spectra change dramatically and where we are now trying to determine the cause of this change. This particular phase coincides with a typical bump in the visual phase diagram [brightness curve] of these stars. There is currently no generally accepted explanation for this dip in the brightness curve, and so our work may help to solve this mystery. We therefore request observing time with TEXES at the IRTF. PROGRAM_ABSTRACT_END