Herbig Ae Young Star's Infrared Spectrum Identified By Hydrocarbon Pentagon-Hexagon Combined Molecules

TL;DR

This study identifies specific hydrocarbon molecules responsible for the infrared spectra of Herbig Ae stars, using quantum chemical calculations to match observed IR features with molecular structures.

Contribution

It introduces a novel approach of using hydrocarbon pentagon-hexagon combined molecules to explain the IR spectra of Herbig Ae stars, providing molecular identifications for observed IR patterns.

Findings

Type-D IR spectra linked to (C12H8)2+ di-cation molecules.

Type-B IR spectra explained by (C23H12)2+ molecules.

Mixture of molecules accounts for spectral variations.

Abstract

Infrared spectrum (IR) of Herbig Ae young stars was reproduced and classified by hydrocarbon pentagon-hexagon combined molecules by the quantum chemical calculation. Observed IR list by B. Acke et al. was categorized to four classes. Among 53 Herbig Ae stars, 26 samples show featured IR pattern named Type-D, which shows common IR peaks at 6.2, 8.3, 9.2, 10.0, 11.3, 12.1, and 14.0 micrometer. Typical star is HD144432. Calculation on di-cation molecule (C12H8)2+ having hydrocarbon one pentagon and two hexagons shows best coincidence at 6.1, 8.2, 9.2, 9.9, 11.3, 12.2, and 14.1 micrometer. There are some variation in Type-D. Spectrum of HD37357 was explained by a mixture with di-cation (C12H8)2+ and tri-cation (C12H8)3+. Ubiquitously observed spectrum Type-B was observed in 12 samples of Acke's list. In case of HD85567, observed 16 peaks were precisely reproduced by a single molecule (C23H12)2+. There is a mixture case with Type-B and Type-D. Typical example was HD142527. In this study, we could identify hidden carrier molecules for all types of IR in Herbig Ae stars.