The {\beta} Pictoris disk imaged by Herschel PACS and SPIRE

TL;DR

This study used Herschel PACS and SPIRE imaging to analyze the debris disk around {eta} Pictoris, revealing its structure, spectral properties, and grain size distribution, with implications for disk dynamics and grain evolution.

Contribution

First detailed Herschel imaging of {eta} Pictoris debris disk across multiple far-infrared wavelengths, providing new insights into its structure and grain size distribution.

Findings

Disk is well resolved at 70, 100, 160 μm with no significant asymmetries.

Spectral index indicates non-equilibrium grain size distribution.

Inner disk grain distribution affected by radiation pressure and possibly non-collisional processes.

Abstract

We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star {\beta} Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 {\mu}m. The surface brightness profiles between 70 and 160 {\mu}m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 {\mu}m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250 - 500 {\mu}m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index ({\beta} = 0.34) indicates that the grain size distribution in the inner disk (<200AU) is inconsistent with a local collisional equilibrium. The size distribution is either modified by non-equilibrium effects, or exhibits a wavy pattern, caused by an under-abundance of impactors which have been removed by radiation pressure.