A Molecular Line Survey of the Carbon-Rich Proto-Planetary Nebula AFGL 2688 in the 3mm and 1.3mm Windows

TL;DR

This study conducts a comprehensive spectral line survey of the proto-planetary nebula AFGL 2688 across multiple frequency ranges, identifying numerous molecules and isotopologues, including first-time detections, to understand its chemical evolution.

Contribution

It provides the first detection of molecules C3H, CH3CN, H2CO, H2CS, and HCO+ in AFGL 2688 and analyzes molecular abundances to study circumstellar chemical evolution.

Findings

143 spectral features identified

First detection of five molecules in AFGL 2688

Isotopic ratios consistent with stellar nucleosynthesis

Abstract

We present a spectral line survey of the proto-planetary nebula AFGL 2688 in the frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using the Arizona Radio Observatory 12m telescope and the Heinrich Hertz Submillimeter Telescope. A total of 143 individual spectral features associated with 32 different molecular species and isotopologues were identified. The molecules C3H, CH3CN, H2CO, H2CS, and HCO+ were detected for the first time in this object. By comparing the integrated line strengths of different transitions, we are able to determine the rotation temperatures, column densities, and fractional abundances of the detected molecules. The C, O, and N isotopic ratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and were found to be consistent with stellar nucleosynthesis theory. Through comparisons of molecular line strengths in asymptotic giant branch stars, proto-planetary nebulae, and planetary nebulae, we discuss the evolution in circumstellar chemistry in the late stages of evolution.