Episodes of Molecular Emission in the Optical Spectrum of IRAS 22272+5435

Abstract

Emission of carbon-bearing molecular lines in multiple optical spectra of IRAS 22272+5435 from 2015 to 2017 is detected, and, for the first time in post–asymptotic giant branch stars, real-time evolution of these features is observed. Specifically, lines of various vibrational transitions of the CN Red system and C _2 Swan system are identified to be in emission. Contrary to the narrow and blueshifted AGB ejecta absorption lines, the emission profiles are broad and redshifted or blueshifted by no more than a few kilometers per second. Molecular emissions appear to be exclusive to spectra corresponding to pulsation phases closer to the star’s light maxima than minima, but there are also such spectra without emissions. The time required for emissions to reach the largest observed intensity or decrease to absorption is around 2–3 weeks. The C _2 Phillips system lines are observed to have emission components as well, but no evidence for their short-term variability is found. It is proposed that the observed emissions originate within few stellar radii above the photosphere.

Keywords

• Post-asymptotic giant branch stars
• Stellar atmospheres
• High resolution spectroscopy
• Circumstellar gas
• Stellar winds
• Shocks