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 C2 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 C2 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.

Pulsation-induced Spectroscopic Variability of IRAS Z02229+6208

“…Note that the inverse P Cygni profiles observed on October 14 are interpreted usually as the result of infalling matter. We recently observed broad emissions near light maximums in the spectra of IRAS 22272+5435 (Puķıtis et al 2023). Thus, the character of spectroscopic variation for IRAS Z02229+6208 was found to be similar to that observed for IRAS 22272+5435 (Začs et al 2016;Začs & Puķıtis 2021;Puķıtis et al 2023) and seems to be typical for the atmospheres of carbon-rich early post-AGB stage stars.…”

“…We recently observed broad emissions near light maximums in the spectra of IRAS 22272+5435 (Puķıtis et al 2023). Thus, the character of spectroscopic variation for IRAS Z02229+6208 was found to be similar to that observed for IRAS 22272+5435 (Začs et al 2016;Začs & Puķıtis 2021;Puķıtis et al 2023) and seems to be typical for the atmospheres of carbon-rich early post-AGB stage stars. Spectroscopic monitoring for a statistically significant sample of early post-AGB stage stars and numerical 3D simulations are needed in order to understand the mechanisms of dynamical and chemical evolution during the transition time from the AGB to post-AGB stage.…”

“…The 21 μm emission feature has been identified in the each of monitored carbon-rich PPNs. The spectroscopic variability, large-scale convective flow, shock waves, and cool outflow attributed to pulsations with a period of 132 days are confirmed for the bright carbon-rich PPN IRAS 22272+5435 (Začs et al 2016;Začs & Puķıtis 2021;Puķıtis et al 2023).…”