Kinematic structure of the atmosphere and envelope of the post-AGB star HD 56126

We present a detailed analysis of the optical spectrum of the post-AGB star HD 56126 (IRAS 07134+1005) based on observations made with the echelle spectrographs of the 6-m telescope of the Special Astrophysical Observatory with resolutions of R = 25 000 and 60 000 at 4012-8790 angstrom. The profiles of strong lines (HI; FeII, YII, BaII absorption lines, etc.) formed in the expanding atmosphere at the base of the stellar wind display complex and variable shapes. To study the kinematics of the atmosphere, the velocities of individual features in these profiles must be measured. Differential line shifts of up to Delta V-r = 15-30 km/s have been detected from the lines of metals and molecular fetures. The stellar atmosphere simultaneously contains both expanding layers and layers falling onto the star. A comparison of the data for different times demonstrates that both the radial velocity and the overall velocity pattern are variable. The position of the molecular spectrum is stable, implying stability of the expansion velocity of the circumstellar envelope around HD 56126 detected in observations in the C-2 and NaI lines.