A spectral line survey of NGC 7027 at millimeter wavelengths

TL;DR

This paper presents a detailed millimeter wavelength spectral line survey of the planetary nebula NGC 7027, identifying molecular and recombination lines, and analyzing physical conditions and chemical processes in its envelope.

Contribution

It provides the first comprehensive spectral line survey of NGC 7027 at millimeter wavelengths, identifying molecular species and analyzing their abundances and physical conditions.

Findings

Detected 67 spectral lines, including 21 molecular and 32 recombination lines.

Found overabundance of N2H+ and underabundance of CS and HNC, indicating X-ray and shock influence.

Evidence suggests complex chemistry influenced by high-energy processes.

Abstract

We report on a recent spectral line survey of the planetary nebula (PN) NGC 7027 using the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at millimeter wavelengths. The spectra covering the frequency ranges 71--111GHz, 157--161GHz, and 218--267GHz were obtained with a typical sensitivity of rms<8mK. A total of 67 spectral lines are detected, 21 of which are identified with 8 molecular species, 32 with recombination lines from hydrogen and helium, and 14 remains unidentified. As the widths of emission lines from CO, other neutral molecules, molecular ions, as well as recombination of H+ and He+ are found to be different with each other, the line strengths and profiles are used to investigate the physical conditions and chemical processes of the neutral envelope of NGC 7027. The column densities and fractional abundances relative to H2 of the observed molecular species are calculated and compared with predictions from chemical models. We found evidence for overabundance of N2H+ and underabundance of CS and HNC in NGC 7027, suggesting that X-ray emission and shock wave may play an important role in the chemistry of the hot molecular envelope of the young PN.