Dust and Polycyclic Aromatic Hydrocarbon in the Pre-Transitional Disk around HD 169142

TL;DR

This study models the dust and PAH emission in the pre-transitional disk of HD 169142, revealing complex dust structures and PAH features that inform planet formation processes.

Contribution

It presents a combined spectral and spatial modeling of dust and PAHs in the disk, incorporating porous dust and PAH features with detailed disk structure.

Findings

Porous dust model fits the SED across IR to millimeter wavelengths.

PAH emission features are well reproduced by the model.

Ice mantle accretion occurs between 16 and 60 AU, overlapping with PAH emission region.

Abstract

The pre-transitional disk around the Herbig Ae star HD 169142 shows a complex structure of possible ongoing planet formation in dust thermal emission from the near infrared (IR) to millimeter wavelength range. Also, a distinct set of broad emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 $\mu$m, commonly attributed to polycyclic aromatic hydrocarbons (PAHs), are detected prominently in the HD 169142 disk. We model the spectral energy distribution (SED) as well as the PAH emission features of the HD 169142 disk simultaneously with porous dust and astronomical-PAHs taking into account the spatially resolved disk structure. Our porous dust model consisting of three distinct components that are primarily concentrated in the inner ring, middle ring, and outer disk, respectively, provides an excellent fit to the entire SED, and the PAH model closely reproduces the observed PAH features. The accretion of ice mantles onto porous dust aggregates occurs between ~16 AU and 60 AU, which overlaps with the spatial extent (~50 AU) of the observed PAH emission features. Finally, we discuss the role of PAHs in the formation of planets possibly taking place in the HD 169142 system.