Spectroscopic variability of IRAS22272+5435

Abstract

A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS22272+5435 (HD235858), along with a simultaneous monitoring of its radial velocity and $BVR_C$ magnitudes. The object is known to vary in light, color, and velocity due to pulsation with a period of 132 days. The light and color variations are accompanied by significant changes in spectral features, most of which are identified as lines of carbon-bearing molecules. According to the observations, the $C_2$ Swan system and CN Red system lines are stronger near the light minimum. A photospheric spectrum of the central star was calculated using new self-consistent atmospheric models. The observed intensity variations in the $C_2$ Swan system and CN Red system lines were found to be much larger than expected if due solely to the temperature variation in the atmosphere of the pulsating star. In addition, the molecular lines are blueshifted relative to the photospheric velocity. The site of formation of the strong molecular features appears to be a cool outflow triggered by the pulsation. The variability in atomic lines seems to be mostly due variations of the effective temperature during the pulsation cycle. The profiles of strong atomic lines are split, and some of them are variable in a time scale of a week or so, probably because of shock waves in the outer atmosphere.