Short-term Spectroscopic Variability of the Early Post-AGB Stage Star IRAS 22272+5435

Abstract

High-resolution spectra gathered during an extensive monitoring of IRAS 22272+5435 are inspected to search for spectroscopic variability in the time span of less than 2 weeks. Significant variation 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 a decrease of its equivalent width. The inward flow of increasing velocity from ≃14.4–21.6 km s⁻¹ was confirmed in the atmosphere, propagating ∼25 R_☉ 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 and shock waves in the extended atmosphere of a cool pulsating post-AGB star.