Spectroscopic variability of IRAS22272+5435

TL;DR

This study presents high-resolution spectroscopic observations of the proto-planetary nebula IRAS22272+5435, revealing complex molecular and atomic line variability linked to pulsation, outflows, and shock phenomena in its atmosphere.

Contribution

It provides detailed analysis of molecular and atomic spectral variability in IRAS22272+5435, highlighting the role of pulsation-induced outflows and shocks, and introduces new atmospheric models for the central star.

Findings

Molecular lines are stronger near light minimum.

Molecular features originate from a pulsation-triggered cool outflow.

Atomic line profiles show variability likely due to shock waves.

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.