Aliphatics and Aromatics in the Universe: The Pre-JWST Era
X.J. Yang, Aigen Li

TL;DR
This paper develops a theoretical method to determine the aliphatic content in PAHs from infrared emission features, using pre-JWST data to estimate aliphatic fractions and analyze their variation across different astrophysical environments.
Contribution
It introduces a framework for quantifying aliphatic fractions in PAHs from emission ratios, aiding future JWST observations of aliphatics and aromatics in space.
Findings
Median aliphatic fraction is 5.4%.
Highest aliphatic fractions are in protoplanetary nebulae with cool stars.
Starlight intensity influences PAH aliphaticity.
Abstract
The so-called "unidentified infrared emission" (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 micron ubiquitously seen in a wide variety of astrophysical regions are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. Astronomical PAHs often have an aliphatic component (e.g., aliphatic sidegroups like methyl --CH3 may be attached as functional groups to PAHs) as revealed by the detection in many UIE sources of the aliphatic C--H stretching feature at 3.4 micron. With its unprecedented sensitivity, unprecedented spatial resolution and high spectral resolution, the James Webb Space Telescope (JWST) holds great promise for evolutionizing the studies of aliphatics and aromatics in the universe. To facilitate analyzing JWST observations, we present a theoretical framework for determining the aliphatic fractions (\eta_ali) of PAHs, the fractions of C atoms in aliphatic…
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Taxonomy
TopicsAstrophysics and Star Formation Studies · Stellar, planetary, and galactic studies · Astronomy and Astrophysical Research
