Herschel discovery of a new class of cold, faint debris discs

TL;DR

Herschel observations reveal a new class of extremely cold, faint debris discs around mature stars, characterized by low temperatures (~22 K) and luminosities similar to the Solar System's Kuiper belt, challenging existing models.

Contribution

This study reports the discovery of the coldest and faintest debris discs around mature stars, identified through Herschel PACS data, expanding understanding of debris disc diversity.

Findings

Infrared excesses at 160 microns indicate cold debris discs.

Discs are spatially resolved with sizes 115-250 AU.

Temperatures are estimated to be ≤ 22 K, with luminosities near 10^-6.

Abstract

We present Herschel PACS 100 and 160 micron observations of the solar-type stars alpha Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel Open Time Key Programme (OTKP) DUNES (DUst around NEarby S tars). Our observations show small infrared excesses at 160 micron for all three stars. HD 210277 also shows a small excess at 100 micron, while the 100 micron fluxes of alpha Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. alpha Men and HD 88230 are spatially resolved in the PACS 160 micron images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from ~ 115 to ~ 250 AU. The estimated black body temperatures from the 100 and 160 micron fluxes are $\lesssim$ 22 K, while the fractional luminosity of the cold dust is Ldust/Lstar ~ 10E-6, close to the luminosity of the Solar-System's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars and cannot easily be explained by invoking "classical" debris disc models.