A Spitzer/IRS spectral study of a sample of galactic carbon-rich proto-planetary nebulae

TL;DR

This study analyzes Spitzer/IRS spectra of carbon-rich proto-planetary nebulae, revealing how organic compounds evolve from aliphatic to aromatic forms during stellar evolution.

Contribution

It provides detailed spectral analysis of PPNs, demonstrating the gradual chemical transformation of organic compounds as stars evolve.

Findings

Most PPNs show the 21 micron emission feature.

Spectral features vary in strength and peak wavelength.

Organic compounds transition from aliphatic to aromatic.

Abstract

Recent infrared spectroscopic observations have shown that proto-planetary nebulae (PPNs) are sites of active synthesis of organic compounds in the late stages of stellar evolution. This paper presents a study of Spitzer/IRS spectra for a sample of carbon-rich PPNs, all except one of which show the unidentified 21 micron emission feature. The strengths of the aromatic infrared band (AIB), 21 micron, and 30 micron features are obtained by decomposition of the spectra. The observed variations in the strengths and peak wavelengths of the features support the model that the newly synthesized organic compounds gradually change from aliphatic to aromatic characteristics as stars evolve from PPNs to planetary nebulae.