4 $\mathsf{\mu}$m spectra of AGB stars I. Observations

We present times series of high resolution spectra of AGB variables at 4 μ m. Line profiles from the major contributors to the spectra of oxygen-rich stars at 4 μ m, OH, H 2 O, HCl and SiO, are examined. The velocity as well as shape variations of these profiles with time are discussed. The line profiles investigated frequently have emission and multiple absorption components. The changes with time of the 4 μ m region lines do not always follow the cyclic variability seen in NIR spectra and in the photometric light curve. We interpret and discuss the results qualitatively considering comparing the spectral variability with that of the well behaved 1.6 μ m region and of dynamical model atmospheres. Miras and semiregular variables are compared. The origins of non-periodic behavior are discussed, including the role of spatial inhomogeneities in the stellar atmosphere.