CO second overtone line variability in three carbon-rich early post-AGB stage stars

Abstract

Near-infrared CO molecular lines are suggested to be linked with dynamic processes in post-AGB stars; however, they have not been investigated at high spectral resolution. CO second overtone line variability in the H-band is presented for the cool carbon-rich post-AGB stars IRAS 22272+5435, IRAS Z02229+6208, and IRAS 20000+3239. CO features are observed to change intensity, shape, and radial velocity as well as switch between emission and absorption during the pulsation cycle. At all times, the CO line positions are located no more than around 10 km/s away from the systemic velocity. Molecular line variation is qualitatively similar in all three stars, and it appears that the site of formation is the extended atmosphere. Emission in CO lines tends to be strongest during pulsation phases close to light maximum, and weakest emission or absorption tends to be seen when close to light minimum, resembling the behaviour in CN Red and C${}_2$ Swan system lines at shorter wavelengths. The connection of molecular line variability with pulsation of the star could be related to a shock that traverses the atmosphere once per pulsation cycle.

References in corpus (13)

• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• Post-Asymptotic Giant Branch Evolution of Low- and Intermediate-Mass Stars. Preliminary Results
• New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae
• The WISE View of RV Tauri Stars
• Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)
• On the CO Near-IR Band and the Line Splitting Phenomenon in the Yellow Hypergiant Rho Cassiopeiae
• Studies of Variability in Proto-Planetary Nebulae: II. Light and Velocity Curve Analyses of Iras 22272+5435 and 22223+4327
• DECH: Software Package for Astronomical Spectral Data Processing and Analysis
• Spectroscopic variability of IRAS22272+5435
• Variability in Protoplanetary Nebulae: IX. Evidence for Evolution in a Decade
• Infrared Spectroscopic Study of a Selection of AGB and Post-AGB Stars
• Integral field spectroscopy of H2 and CO emission in IRAS 18276-1431: evidence for ongoing post-AGB mass loss