Evidence of large-scale flow in the outer atmosphere of the early post-AGB stage star IRAS22272+5435

High-resolution spectra gathered during an extensive monitoring of IRAS22272+5435 are inspected to search for spectroscopic variability in the time span of less than two weeks with a time resolution of 1-2 days. Significant variations are found both in the intensity and position of CN (1,0) Red System lines near the light maximum, when the star is the hottest. The intensity of variable CN lines correlates with their Doppler redshift – an increase in the radial velocity leads to decrease of its equivalent width. The inward flow of increasing velocity from about 14.4 to 21.6 km/s was confirmed in the atmosphere, propagating about 25 solar radii toward the mass center of the star in 11 days. The variability of CN (1,0) lines are accompanied by changes in the red wings of strong low-excitation lines. The observed short-term variations are attributed to large-scale convective flows in the extended atmosphere of a cool pulsating post-AGB star. At the light minimum, when the star is the coolest, the CN lines are much stronger and blueshifted by about -5.0 km/s on average relative to the photospheric atomic lines, however, a significant variation was not found during the time span of 7 days.