Molecules in the carbon-rich protoplanetary nebula CRL 2688

TL;DR

This study reports extensive molecular line observations of the carbon-rich protoplanetary nebula CRL 2688, revealing new molecular species and lines, and discusses the implications for circumstellar chemistry beyond standard models.

Contribution

The paper provides the first comprehensive molecular line catalog for CRL 2688 and highlights discrepancies with standard circumstellar envelope models.

Findings

196 transition lines from 38 molecules detected

153 lines and 13 species are newly reported for this object

Molecular abundances challenge standard circumstellar models

Abstract

We present observations of the carbon-rich protoplanetary nebula (PPN) CRL 2688 made with the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope in the 3mm and 2mm bands. In total, 196 transition lines belonging to 38 molecular species and isotopologues are detected, among which, to our best knowledge, 153 transition lines and 13 species are the first report for this object. Additionally, in order to contribute to future research, we have collected observational data on the molecular lines of CRL 2688 from the literature and compiled them into a single unified catalog. We find that the molecular abundance of CRL 2688 cannot be explained by the standard model of a circumstellar envelope. The implications of metal-bearing molecules on circumstellar chemistry are discussed.