INFRARED-SPECTROSCOPY OF CEPHEIDS .2. LINE-PROFILES FROM DIFFERENT ATMOSPHERIC LAYERS

We present the first analysis of high-resolution infrared spectra at 1.08 and 1.6 μm for classical Cepheid variables. Three of the seven program stars were observed with complete phase coverage. The photospheric lines in the spectra were measured for asymmetries and compared to synthetic profiles from model atmospheres. An additional absorption component is shown to appear at certain phases in the 1.08 μm lines of X Sgr, δ Cep, η Aql, and possibly T Mon. The kinematics of this component is similar to that observed in line-doubling infrared spectra of Mira variables. This resemblance suggests the existence of pulsationally driven shock waves in the atmospheres of Cepheids to explain their infrared line asymmetries and splitting. With additional data and carefully determined projection factors, we confirm the systematically larger BaadeWesselink radii that we derived earlier for η Aql and X Sgr. The magnitude of the effect is about 20%.