Exploring cyanopolyynes towards the C-rich post-AGB star IRAS 22272+5435

Cyanopolyynes are a class of long carbon-chain molecules that are widely distributed in interstellar clouds, but their presence in the circumstellar envelopes (CSEs) of evolved stars appears to be limited to only a few well-studied sources. This study aims to search for the presence of cyanopolyynes in the CSE of the C-rich post-asymptotic giant branch (post-AGB) star IRAS 22272+5435 through observational analysis and radiative transfer modelling. Observations were conducted using the Tianma 65 m radio telescope (TMRT) at
15 GHz and the Purple Mountain Observatory (PMO) 13.7 m MM-Wave telescope at
90 GHz. The HCN and HCN transitions were clearly detected in the PMO 13.7 m data, while no significant signals of other cyanopolyynes were detected with TMRT. Based on the observed HCN line, we constructed a spherically symmetric non-thermodynamic equilibrium radiative transfer model, extrapolating the abundance distribution structure from the well-studied C-rich AGB star IRC+10216 to IRAS 22272+5435. The model successfully reproduces the observed HCN and HCN profiles and predicts the line intensities of HCN and HCN. Although the results suggest that these heavier cyanopolyynes may be present in the CSE, their detections are hindered by the large distance and significant beam dilution effects. This study provides valuable observational constraints and theoretical insights into the formation and evolution of carbon-chain molecules in post-AGB environments.