Interferometric molecular line observations toward the 21 μm protoplanetary nebula IRAS 06530-0213

Abstract

The identification of the $21\mu \mathrm{m}$ feature in some protoplanetary nebulae remains a longstanding puzzle, whose interpretation requires characterization of the molecular gas environments of associated sources. Here, we present high-resolution interferometric observations from the Northern Extended Millimeter Array toward the $21\mu \mathrm{m}$ protoplanetary nebula IRAS 06530-0213. Multiple molecular transitions of $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$, ${\mathrm{C}}_4\mathrm{H}$, and $\mathrm{Si}{\mathrm{C}}_2$ are detected and spatially resolved. We analyze these spectral lines alongside previously reported CO and ${}^{13}\mathrm{CO}$ emission toward this source. Differing from the extended barrel-like molecular structure traced by CO and ${}^{13}\mathrm{CO}$, $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$ and ${\mathrm{C}}_4\mathrm{H}$ are predominantly concentrated in the inner low-latitude equatorial zones. Reproducing the observed morphology requires $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$ to possess a more inwardly concentrated abundance distribution compared with CO and ${}^{13}\mathrm{CO}$, implying that the inner equatorial regions provide favorable conditions for carbon-chain chemistry.

29 pages, 11 figures, 2 tables. Accepted for AJ